formualizer_eval/engine/

eval.rs

use crate::SheetId;
use crate::arrow_store::{OverlayFragment, OverlayValue, SheetStore};
use crate::engine::arena::AstNodeId;
use crate::engine::eval_delta::{DeltaCollector, DeltaMode, EvalDelta};
use crate::engine::ingest_pipeline::{DependencyPlanRow, FormulaAstInput};
use crate::engine::live_edges::{LiveEdgeCollector, RecordingContext};
use crate::engine::live_graph::analyze_live_graph;
use crate::engine::lookup_index_cache::{
    BuildOutcome, LookupAxis, LookupIndex, LookupIndexCache, LookupIndexCacheReport,
    LookupIndexKey, estimate_bytes,
};
use crate::engine::named_range::{NameScope, NamedDefinition};
use crate::engine::range_view::RangeView;
use crate::engine::row_visibility::RowVisibilityState;
use crate::engine::spill::{RegionLockManager, SpillMeta, SpillShape};
use crate::engine::virtual_deps::VirtualDepBuilder;
use crate::engine::{
    CycleDetection, CyclePolicy, DependencyGraph, EvalConfig, FormulaIngestBatch,
    FormulaIngestRecord, FormulaIngestReport, FormulaParseDiagnostic, FormulaParsePolicy,
    FormulaPlaneMode, RowVisibilitySource, ScheduleUnit, Scheduler, VertexId, VertexKind,
    VisibilityMaskMode,
};
use crate::formula_plane::placement::{
    CandidateAnalysis, FormulaPlacementCandidate, FormulaPlacementResult, PlacementFallbackReason,
    place_candidate_family_with_analyses, split_candidate_affine_literal_runs,
};
use crate::formula_plane::producer::{
    DirtyProjectionRule, FormulaConsumerReadIndex, FormulaProducerId, FormulaProducerResultIndex,
    FormulaProducerWork, ProducerDirtyDomain, SpanReadSummary,
};
use crate::formula_plane::region_index::{DirtyDomain, Region};
use crate::formula_plane::runtime::{
    FormulaPlane, FormulaSpanId, FormulaSpanRef, PlacementCoord, PlacementDomain, ResultRegion,
};
use crate::formula_plane::scheduler::{
    MixedSchedule, MixedScheduleFallbackReason, build_mixed_schedule,
};
#[cfg(test)]
use crate::formula_plane::span_eval::SpanEvalReport;
use crate::formula_plane::span_eval::{SpanComputedWriteSink, SpanEvalTask, SpanEvaluator};
use crate::formula_plane::structural::relocate_ast_for_template_placement;
use crate::formula_plane::structural_shift::{SpanShiftPlan, StructuralOp, classify_span_for_op};
use crate::interpreter::Interpreter;
use crate::reference::{CellRef, Coord, RangeRef};
use crate::traits::FunctionProvider;
use crate::traits::{EvaluationContext, ReferenceInfo, Resolver};
use chrono::Timelike;
use formualizer_common::{
    CoordBuildHasher, LiteralValue, col_letters_from_1based, parse_a1_1based,
};
use formualizer_parse::parser::ReferenceType;
use formualizer_parse::{ASTNode, ASTNodeType, ExcelError, ExcelErrorKind};
use rayon::ThreadPoolBuilder;
use rustc_hash::{FxHashMap, FxHashSet};
use std::collections::{BTreeMap, BTreeSet, VecDeque};
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};

type StagedFormulaEntry = (u32, u32, String);

/// Per-sheet staged-formula store (NOTE(#126) follow-up).
///
/// Ingest consumers (`build_graph_all`/`build_graph_for_sheets`) walk staged
/// entries in INSERTION order, so the order-preserving `Vec` stays the
/// canonical storage; a `(row, col) → index` map removes the linear dup-scan
/// that made `stage_formula_text`/`get_staged_formula_text` O(staged-on-sheet)
/// per call (O(n²) for an n-formula deferred load on one sheet — ~570 ms for
/// 50k stages, release, before the index). `stage`/`get` are O(1);
/// `remove` keeps the old O(n) `Vec::remove` (rare path, order preserved).
#[derive(Debug, Default, Clone)]
pub(crate) struct StagedSheet {
    entries: Vec<StagedFormulaEntry>,
    index: FxHashMap<(u32, u32), usize>,
}

impl StagedSheet {
    fn stage(&mut self, row: u32, col: u32, text: String) {
        match self.index.entry((row, col)) {
            std::collections::hash_map::Entry::Occupied(slot) => {
                self.entries[*slot.get()].2 = text;
            }
            std::collections::hash_map::Entry::Vacant(slot) => {
                slot.insert(self.entries.len());
                self.entries.push((row, col, text));
            }
        }
    }

    fn remove(&mut self, row: u32, col: u32) -> Option<String> {
        let idx = self.index.remove(&(row, col))?;
        let (_, _, text) = self.entries.remove(idx);
        // `Vec::remove` shifted everything after `idx` left by one.
        for slot in self.index.values_mut() {
            if *slot > idx {
                *slot -= 1;
            }
        }
        Some(text)
    }

    fn get(&self, row: u32, col: u32) -> Option<&str> {
        self.index
            .get(&(row, col))
            .map(|&i| self.entries[i].2.as_str())
    }

    fn len(&self) -> usize {
        self.entries.len()
    }

    fn is_empty(&self) -> bool {
        self.entries.is_empty()
    }

    /// Consume into the insertion-ordered entry list (ingest order).
    fn into_entries(self) -> Vec<StagedFormulaEntry> {
        self.entries
    }
}

type StagedFormulaMap = std::collections::HashMap<String, StagedSheet>;

fn producer_dirty_to_span_dirty(
    dirty: ProducerDirtyDomain,
    span_ref: FormulaSpanRef,
) -> DirtyDomain {
    match dirty {
        ProducerDirtyDomain::Whole => DirtyDomain::WholeSpan(span_ref),
        ProducerDirtyDomain::Cells(cells) => DirtyDomain::Cells(cells),
        ProducerDirtyDomain::Regions(regions) => DirtyDomain::Regions(regions),
    }
}
type PreparedFormulaBatches = Vec<FormulaIngestBatch>;
type StagedFormulaBatches = Vec<(String, Vec<StagedFormulaEntry>)>;
type FormulaPlaneMixedScheduleBuild = (
    MixedSchedule,
    BTreeMap<crate::formula_plane::runtime::FormulaSpanId, FormulaSpanRef>,
    u64,
    Vec<VertexId>,
);

type PlannedFormulaMaterialize = BTreeMap<String, Vec<(u32, u32, AstNodeId, DependencyPlanRow)>>;

// Computed-write coalescing pays a fixed grouping/planning cost. For very narrow
// layers there is not enough work to amortize it, and the direct point-write path
// is faster while preserving the same visibility semantics.
const COMPUTED_WRITE_COALESCING_MIN_LAYER_WIDTH: usize = 8;

#[derive(Debug, Clone, PartialEq)]
pub(crate) enum ComputedWrite {
    Cell {
        seq: u64,
        sheet_id: SheetId,
        row0: u32,
        col0: u32,
        value: OverlayValue,
    },
    Rect {
        seq: u64,
        sheet_id: SheetId,
        sr0: u32,
        sc0: u32,
        values: Vec<Vec<OverlayValue>>,
    },
}

impl ComputedWrite {
    #[inline]
    pub(crate) fn seq(&self) -> u64 {
        match self {
            ComputedWrite::Cell { seq, .. } | ComputedWrite::Rect { seq, .. } => *seq,
        }
    }
}

#[derive(Debug, Default)]
pub(crate) struct ComputedWriteBuffer {
    writes: Vec<ComputedWrite>,
    next_seq: u64,
    estimated_bytes: usize,
}

impl ComputedWriteBuffer {
    const ENTRY_BASE_BYTES: usize = 32;

    #[inline]
    pub(crate) fn is_empty(&self) -> bool {
        self.writes.is_empty()
    }

    #[inline]
    pub(crate) fn len(&self) -> usize {
        self.writes.len()
    }

    #[inline]
    pub(crate) fn estimated_bytes(&self) -> usize {
        self.estimated_bytes
    }

    #[inline]
    pub(crate) fn writes(&self) -> &[ComputedWrite] {
        &self.writes
    }

    pub(crate) fn push_cell(
        &mut self,
        sheet_id: SheetId,
        row0: u32,
        col0: u32,
        value: OverlayValue,
    ) {
        let seq = self.next_sequence();
        self.estimated_bytes = self
            .estimated_bytes
            .saturating_add(Self::estimate_value_bytes(&value));
        self.writes.push(ComputedWrite::Cell {
            seq,
            sheet_id,
            row0,
            col0,
            value,
        });
    }

    pub(crate) fn push_rect(
        &mut self,
        sheet_id: SheetId,
        sr0: u32,
        sc0: u32,
        values: Vec<Vec<OverlayValue>>,
    ) {
        let seq = self.next_sequence();
        let added = values
            .iter()
            .flat_map(|row| row.iter())
            .map(Self::estimate_value_bytes)
            .fold(0usize, usize::saturating_add);
        self.estimated_bytes = self.estimated_bytes.saturating_add(added);
        self.writes.push(ComputedWrite::Rect {
            seq,
            sheet_id,
            sr0,
            sc0,
            values,
        });
    }

    pub(crate) fn clear(&mut self) {
        self.writes.clear();
        self.estimated_bytes = 0;
    }

    fn take_writes(&mut self) -> Vec<ComputedWrite> {
        self.estimated_bytes = 0;
        std::mem::take(&mut self.writes)
    }

    fn next_sequence(&mut self) -> u64 {
        let seq = self.next_seq;
        self.next_seq = self.next_seq.wrapping_add(1);
        seq
    }

    #[inline]
    fn estimate_value_bytes(value: &OverlayValue) -> usize {
        Self::ENTRY_BASE_BYTES.saturating_add(value.estimated_payload_bytes())
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
struct ComputedWriteChunkKey {
    sheet_id: SheetId,
    col0: u32,
    chunk_idx: usize,
    chunk_start_row0: u32,
}

#[derive(Debug, Clone, PartialEq)]
pub(crate) struct ComputedWriteChunkEntryPlan {
    pub(crate) row_in_chunk: usize,
    pub(crate) seq: u64,
    pub(crate) value: OverlayValue,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) enum ComputedWriteChunkPlanShape {
    Point,
    SparseOffsets {
        entries: usize,
        span_len: usize,
    },
    DenseRange {
        start: usize,
        len: usize,
    },
    RunRange {
        start: usize,
        len: usize,
        runs: usize,
    },
}

#[derive(Debug, Clone, PartialEq)]
pub(crate) struct ComputedWriteChunkPlan {
    pub(crate) sheet_id: SheetId,
    pub(crate) col0: u32,
    pub(crate) chunk_idx: usize,
    pub(crate) chunk_start_row0: u32,
    pub(crate) entries: Vec<ComputedWriteChunkEntryPlan>,
    pub(crate) shape: ComputedWriteChunkPlanShape,
}

#[derive(Debug, Clone, Default, PartialEq)]
pub(crate) struct ComputedWriteCoalescingPlan {
    pub(crate) chunks: Vec<ComputedWriteChunkPlan>,
    pub(crate) input_cells: usize,
    pub(crate) coalesced_cells: usize,
    pub(crate) overwritten_cells: usize,
}

impl ComputedWriteCoalescingPlan {
    #[inline]
    pub(crate) fn is_empty(&self) -> bool {
        self.chunks.is_empty()
    }
}

impl ComputedWriteChunkPlan {
    fn from_group(
        key: ComputedWriteChunkKey,
        mut entries: Vec<ComputedWriteChunkEntryPlan>,
    ) -> (Self, usize) {
        entries.sort_by_key(|entry| (entry.row_in_chunk, entry.seq));
        let input_len = entries.len();
        let mut coalesced: Vec<ComputedWriteChunkEntryPlan> = Vec::with_capacity(input_len);
        for entry in entries {
            if let Some(prev) = coalesced.last_mut()
                && prev.row_in_chunk == entry.row_in_chunk
            {
                *prev = entry;
                continue;
            }
            coalesced.push(entry);
        }
        let overwritten = input_len.saturating_sub(coalesced.len());
        let shape = Self::classify_shape(&coalesced);
        (
            Self {
                sheet_id: key.sheet_id,
                col0: key.col0,
                chunk_idx: key.chunk_idx,
                chunk_start_row0: key.chunk_start_row0,
                entries: coalesced,
                shape,
            },
            overwritten,
        )
    }

    fn classify_shape(entries: &[ComputedWriteChunkEntryPlan]) -> ComputedWriteChunkPlanShape {
        debug_assert!(!entries.is_empty());
        if entries.len() == 1 {
            return ComputedWriteChunkPlanShape::Point;
        }

        let start = entries[0].row_in_chunk;
        let end = entries[entries.len() - 1].row_in_chunk;
        let span_len = end.saturating_sub(start).saturating_add(1);
        if span_len != entries.len() {
            return ComputedWriteChunkPlanShape::SparseOffsets {
                entries: entries.len(),
                span_len,
            };
        }

        let runs = Self::run_count(entries);
        if runs < entries.len() {
            ComputedWriteChunkPlanShape::RunRange {
                start,
                len: entries.len(),
                runs,
            }
        } else {
            ComputedWriteChunkPlanShape::DenseRange {
                start,
                len: entries.len(),
            }
        }
    }

    fn run_count(entries: &[ComputedWriteChunkEntryPlan]) -> usize {
        let mut runs = 0usize;
        let mut prev: Option<&OverlayValue> = None;
        for entry in entries {
            if prev != Some(&entry.value) {
                runs = runs.saturating_add(1);
                prev = Some(&entry.value);
            }
        }
        runs
    }
}

pub struct Engine<R> {
    pub(crate) graph: DependencyGraph,
    resolver: R,
    pub config: EvalConfig,
    workbook_load_limits: crate::engine::WorkbookLoadLimits,
    /// Clock for volatile date/time builtins, wrapped in a per-recalc
    /// snapshot: sampled once at the start of every evaluation request
    /// ([`Self::begin_evaluation_request`]) so all `NOW()`/`TODAY()` reads in
    /// one recalc — including SCC iteration passes — agree (spec §7.11).
    clock: crate::timezone::SnapshotClock,
    thread_pool: Option<Arc<rayon::ThreadPool>>,
    pub recalc_epoch: u64,
    snapshot_id: std::sync::atomic::AtomicU64,
    topology_epoch: u64,
    cached_static_schedule: Option<CachedScheduleEntry>,
    spill_mgr: ShimSpillManager,
    /// Arrow-backed storage for sheet values (Phase A)
    arrow_sheets: SheetStore,
    /// True if any edit after bulk load; disables Arrow reads for parity
    has_edited: bool,
    /// Overlay compaction counter (Phase C instrumentation)
    overlay_compactions: u64,

    // Overlay memory observability / budget (ticket 503)
    computed_overlay_bytes_estimate: usize,
    computed_overlay_mirroring_disabled: bool,
    /// When true, RangeView resolution materializes from graph/Arrow base per-cell.
    /// This preserves correctness if we stop mirroring formula/spill outputs into computed overlays.
    pub(crate) force_materialize_range_views: bool,
    // Pass-scoped cache for Arrow used-row bounds per column
    row_bounds_cache: std::sync::RwLock<Option<RowBoundsCache>>,
    // Snapshot-scoped final used-axis bounds for open-ended references.
    used_axis_bounds_cache: std::sync::RwLock<Option<UsedAxisBoundsCache>>,
    lookup_index_cache: LookupIndexCache,
    source_cache: Arc<std::sync::RwLock<SourceCache>>,
    /// Staged formulas by sheet when `defer_graph_building` is enabled.
    staged_formulas: StagedFormulaMap,
    /// Per-sheet row visibility sidecar state.
    row_visibility: FxHashMap<SheetId, RowVisibilityState>,
    /// Cached row visibility masks keyed by sheet/span/mode/version.
    row_visibility_mask_cache: std::sync::RwLock<
        FxHashMap<VisibilityMaskCacheKey, std::sync::Arc<arrow_array::BooleanArray>>,
    >,
    /// Non-fatal malformed formula diagnostics captured during ingest/graph-build.
    formula_parse_diagnostics: Vec<FormulaParseDiagnostic>,
    /// Last centralized formula ingest report.
    last_formula_ingest_report: Option<FormulaIngestReport>,
    /// Aggregate centralized formula ingest report for this engine.
    formula_ingest_report_total: FormulaIngestReport,
    /// Count of FormulaPlane spans demoted to legacy because one or more of
    /// their member cells participate in a statically-cyclic SCC. A span member
    /// must never be span-evaluated (gotcha G8 of the cycle-architecture track,
    /// refs #112): under `CycleDetection::Static` the cycle stamping would race
    /// span writes, and under `Runtime` SCC members must be evaluated by the
    /// legacy `evaluate_scc_unit` path. Cyclic spans are demoted at
    /// schedule-build time (the earliest point cross-cell cycles through span
    /// producers become visible) so the cycle members land on the legacy graph
    /// path. Observational only.
    formula_plane_cycle_member_span_demotions: u64,
    /// Times the FormulaPlane coordinator failed over to the legacy
    /// primitive because the mixed schedule reported only non-cycle
    /// fallbacks (capacity caps, unsupported projections, missing result
    /// regions). One increment per `evaluate_all`-level bailout — the
    /// cyclic-span demote loop must never spin on these. Observational only.
    formula_plane_capacity_bailouts: u64,
    /// Transient cancellation flag used during evaluation
    active_cancel_flag: Option<Arc<AtomicBool>>,

    /// Engine-level action depth.
    ///
    /// Ticket 614 introduces `Engine::action` as a stable, commit-only transaction surface.
    /// Nested actions are currently disallowed (deterministic rule) and will return an error.
    action_depth: u32,

    // Phase 3b virtual-dependency convergence telemetry
    last_virtual_dep_telemetry: VirtualDepTelemetry,
    virtual_dep_fallback_activations: u64,

    // Runtime-cycle SCC evaluation telemetry (RFC #112, Stage 2)
    last_cycle_telemetry: CycleTelemetry,

    /// SCC members that entered iterative calculation (`CyclePolicy::Iterate`
    /// with a witnessed live cycle) during the current evaluation request.
    ///
    /// Excel re-evaluates circular cells on EVERY recalc (the accumulator
    /// contract, spec §4/§7.6), but this engine's dirty model marks SCC
    /// members clean after a recalc and would otherwise skip them forever.
    /// Resolution: members of iterating SCCs are redirtied volatile-like at
    /// the end of the same recalc that iterated them
    /// ([`Self::redirty_for_next_recalc`], called wherever
    /// `redirty_volatiles` runs). The set is per-recalc, never persisted:
    /// if an edit breaks the cycle, the next recalc's SCC task either does
    /// not exist or settles as phantom, nothing re-registers, and the
    /// redirty chain stops by itself.
    pending_iterative_redirty: Vec<VertexId>,

    /// Final committed values of iterating-SCC members as of the end of the
    /// most recent recalc (spec §4 persistence). In canonical (value-cache
    /// disabled) mode the computed overlay is the ONLY home of a formula's
    /// value, and structural edits clear computed overlays wholesale
    /// (`clear_computed_overlay_after_row/_col`) — destroying iteration
    /// state (accumulators reset to 0; found by the iterate edge corpus).
    /// This snapshot, refreshed by [`Self::redirty_for_next_recalc`], lets
    /// the next SCC task re-seed members whose overlay entry vanished.
    /// Empty unless something iterated — zero cost otherwise.
    iterative_state_values: FxHashMap<VertexId, LiteralValue>,

    /// FormulaPlane authority `indexes_epoch` observed by the most recent
    /// successful `evaluate_all` pass. Used to schedule whole-span work for
    /// any active span the engine has not yet evaluated under the current
    /// indexes generation; subsequent passes use bounded dirty closures.
    formula_plane_indexes_epoch_seen: u64,

    #[cfg(test)]
    last_formula_plane_span_eval_report: Option<SpanEvalReport>,
}

/// Minimal edit surface used by `Engine::action`.
///
/// This wrapper is intentionally thin for ticket 614 (commit-only): it delegates to existing
/// `Engine` edit methods and does not create changelog boundaries or implement rollback.
impl<R: EvaluationContext> Engine<R> {
    pub(crate) fn ingest_pipeline(&mut self) -> crate::engine::ingest_pipeline::IngestPipeline<'_> {
        self.graph.ingest_pipeline(&self.resolver)
    }
}

pub struct EngineAction<'a, R>
where
    R: EvaluationContext,
{
    engine: &'a mut Engine<R>,
    name: String,
    // Optional external ChangeLog pointer used by `Engine::action_with_logger`.
    // Stored as a raw pointer to avoid creating aliasing `&mut` borrows alongside `&mut Engine`.
    log: Option<*mut crate::engine::ChangeLog>,
    // Optional Arrow undo journal used by `Engine::action_atomic`.
    // Stored as a raw pointer to avoid aliasing issues with `&mut Engine`.
    arrow_undo: Option<*mut crate::engine::ArrowUndoBatch>,
    // True when this EngineAction must enforce conservative atomic transaction policy.
    atomic_policy: bool,
}

impl<'a, R> EngineAction<'a, R>
where
    R: EvaluationContext,
{
    #[inline]
    fn addr_for(&mut self, sheet: &str, row: u32, col: u32) -> crate::reference::CellRef {
        let sheet_id = self.engine.graph.sheet_id_mut(sheet);
        let coord = crate::reference::Coord::from_excel(row, col, true, true);
        crate::reference::CellRef::new(sheet_id, coord)
    }

    #[inline]
    pub fn name(&self) -> &str {
        &self.name
    }

    #[inline]
    pub fn set_cell_value(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        value: LiteralValue,
    ) -> Result<(), crate::engine::EditorError> {
        if self.log.is_some() {
            let old_value = self.engine.read_cell_value(sheet, row, col);
            let mut old_formula = self.engine.read_cell_formula_ast(sheet, row, col);
            let addr = self.addr_for(sheet, row, col);
            let Some(log_ptr) = self.log else {
                return Err(crate::engine::EditorError::TransactionFailed {
                    reason: "action_with_logger: missing ChangeLog".to_string(),
                });
            };

            // For atomic journal mode, record computed overlay effects for this cell.
            // Delta-overlay undo is recorded semantically based on old_value/old_formula.
            let old_comp = if self.arrow_undo.is_some() {
                self.engine.read_computed_overlay_cell(sheet, row, col)
            } else {
                None
            };

            self.engine.demote_span_containing_cell_for_write(
                addr.sheet_id,
                addr.coord.row(),
                addr.coord.col(),
            )?;
            if old_formula.is_none() {
                old_formula = self.engine.read_cell_formula_ast(sheet, row, col);
            }

            let delta_old_sem = if old_formula.is_some() {
                None
            } else {
                Some(old_value.clone().unwrap_or(LiteralValue::Empty))
            };

            let start_len = unsafe { (&*log_ptr).len() };

            // Safety: `log_ptr` comes from a unique `&mut ChangeLog` in `Engine::action_with_logger`.
            let log = unsafe { &mut *log_ptr };
            self.engine.edit_with_logger(log, |editor| {
                editor.set_cell_value_with_old_state(
                    addr,
                    value.clone(),
                    old_value.clone(),
                    old_formula.clone(),
                );
            });
            self.engine
                .record_formula_plane_structural_change(StructuralScope::Cell {
                    sheet: addr.sheet_id,
                    row: addr.coord.row(),
                    col: addr.coord.col(),
                });

            if let Some(undo_ptr) = self.arrow_undo {
                // 1) Spill snapshot operations (computed overlay rect restore).
                let new_events = &unsafe { (&*log_ptr).events() }[start_len..];
                let undo = unsafe { &mut *undo_ptr };
                self.engine
                    .record_spill_ops_into_arrow_undo(undo, new_events);

                // 2) Delta/computed overlay single-cell deltas.
                let new_comp = self.engine.read_computed_overlay_cell(sheet, row, col);
                let sheet_id = self.engine.graph.sheet_id_mut(sheet);
                let row0 = row.saturating_sub(1);
                let col0 = col.saturating_sub(1);
                let delta_new_sem = Some(value.clone());
                undo.record_delta_cell(sheet_id, row0, col0, delta_old_sem, delta_new_sem);
                undo.record_computed_cell(sheet_id, row0, col0, old_comp, new_comp);
            }
            Ok(())
        } else {
            self.engine
                .set_cell_value(sheet, row, col, value)
                .map_err(crate::engine::EditorError::from)
        }
    }

    #[inline]
    pub fn set_cell_formula(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        ast: ASTNode,
    ) -> Result<(), crate::engine::EditorError> {
        if self.log.is_some() {
            let old_value = self.engine.read_cell_value(sheet, row, col);
            let mut old_formula = self.engine.read_cell_formula_ast(sheet, row, col);
            let addr = self.addr_for(sheet, row, col);
            let Some(log_ptr) = self.log else {
                return Err(crate::engine::EditorError::TransactionFailed {
                    reason: "action_with_logger: missing ChangeLog".to_string(),
                });
            };

            self.engine.demote_span_containing_cell_for_write(
                addr.sheet_id,
                addr.coord.row(),
                addr.coord.col(),
            )?;
            if old_formula.is_none() {
                old_formula = self.engine.read_cell_formula_ast(sheet, row, col);
            }
            let delta_old = if self.arrow_undo.is_some() {
                if old_formula.is_some() {
                    None
                } else {
                    Some(old_value.clone().unwrap_or(LiteralValue::Empty))
                }
            } else {
                None
            };
            let start_len = unsafe { (&*log_ptr).len() };

            // Safety: `log_ptr` comes from a unique `&mut ChangeLog` in `Engine::action_with_logger`.
            let log = unsafe { &mut *log_ptr };
            self.engine.edit_with_logger(log, |editor| {
                editor.set_cell_formula_with_old_state(addr, ast.clone(), old_value, old_formula);
            });
            self.engine
                .record_formula_plane_structural_change(StructuralScope::Cell {
                    sheet: addr.sheet_id,
                    row: addr.coord.row(),
                    col: addr.coord.col(),
                });

            if let Some(undo_ptr) = self.arrow_undo {
                let new_events = &unsafe { (&*log_ptr).events() }[start_len..];
                let undo = unsafe { &mut *undo_ptr };
                self.engine
                    .record_spill_ops_into_arrow_undo(undo, new_events);
                let delta_new: Option<LiteralValue> = None;
                let sheet_id = self.engine.graph.sheet_id_mut(sheet);
                let row0 = row.saturating_sub(1);
                let col0 = col.saturating_sub(1);
                undo.record_delta_cell(sheet_id, row0, col0, delta_old, delta_new);
            }
            Ok(())
        } else {
            self.engine
                .set_cell_formula(sheet, row, col, ast)
                .map_err(crate::engine::EditorError::from)
        }
    }

    #[inline]
    pub fn set_row_hidden(
        &mut self,
        sheet: &str,
        row_1based: u32,
        hidden: bool,
        source: RowVisibilitySource,
    ) -> Result<(), crate::engine::EditorError> {
        if self.log.is_some() {
            let sheet_id = self.engine.ensure_known_sheet_id(sheet)?;
            let row0 = Engine::<R>::normalize_row_1based(row_1based)?;
            let old_hidden = self
                .engine
                .row_visibility
                .get(&sheet_id)
                .map(|state| state.is_row_hidden(row0, Some(source)))
                .unwrap_or(false);
            if old_hidden == hidden {
                return Ok(());
            }

            let _ = self
                .engine
                .set_row_hidden_by_sheet_id(sheet_id, row0, hidden, source);

            let Some(log_ptr) = self.log else {
                return Err(crate::engine::EditorError::TransactionFailed {
                    reason: "action_with_logger: missing ChangeLog".to_string(),
                });
            };
            unsafe { &mut *log_ptr }.record(crate::engine::ChangeEvent::SetRowVisibility {
                sheet_id,
                row0,
                source,
                old_hidden,
                new_hidden: hidden,
            });

            Ok(())
        } else {
            self.engine
                .set_row_hidden(sheet, row_1based, hidden, source)
        }
    }

    #[inline]
    pub fn set_rows_hidden(
        &mut self,
        sheet: &str,
        start_row_1based: u32,
        end_row_1based: u32,
        hidden: bool,
        source: RowVisibilitySource,
    ) -> Result<(), crate::engine::EditorError> {
        if self.log.is_some() {
            let sheet_id = self.engine.ensure_known_sheet_id(sheet)?;
            let (start_row0, end_row0) =
                Engine::<R>::normalize_row_range_1based(start_row_1based, end_row_1based)?;

            let Some(log_ptr) = self.log else {
                return Err(crate::engine::EditorError::TransactionFailed {
                    reason: "action_with_logger: missing ChangeLog".to_string(),
                });
            };
            let log = unsafe { &mut *log_ptr };

            for row0 in start_row0..=end_row0 {
                let old_hidden = self
                    .engine
                    .row_visibility
                    .get(&sheet_id)
                    .map(|state| state.is_row_hidden(row0, Some(source)))
                    .unwrap_or(false);
                if old_hidden == hidden {
                    continue;
                }

                let _ = self
                    .engine
                    .set_row_hidden_by_sheet_id(sheet_id, row0, hidden, source);

                log.record(crate::engine::ChangeEvent::SetRowVisibility {
                    sheet_id,
                    row0,
                    source,
                    old_hidden,
                    new_hidden: hidden,
                });
            }

            Ok(())
        } else {
            self.engine
                .set_rows_hidden(sheet, start_row_1based, end_row_1based, hidden, source)
        }
    }

    #[inline]
    pub fn insert_rows(
        &mut self,
        sheet: &str,
        before: u32,
        count: u32,
    ) -> Result<crate::engine::ShiftSummary, crate::engine::EditorError> {
        if self.log.is_some() {
            let Some(log_ptr) = self.log else {
                return Err(crate::engine::EditorError::TransactionFailed {
                    reason: "action_atomic: missing ChangeLog".to_string(),
                });
            };

            let sheet_id = self.engine.graph.sheet_id_mut(sheet);
            let before0 = before.saturating_sub(1);
            let op = StructuralOp::InsertRows {
                sheet_id,
                before: before0,
                count,
            };
            self.engine.demote_spans_for_structural_op(
                op,
                Engine::<R>::structural_row_region(sheet_id, before0),
            )?;

            // Graph structural insert (logged) - no snapshot bump.
            let summary = {
                let log = unsafe { &mut *log_ptr };
                let mut out: Result<crate::engine::ShiftSummary, crate::engine::EditorError> =
                    Ok(crate::engine::ShiftSummary::default());
                self.engine.edit_with_logger(log, |editor| {
                    out = editor.insert_rows(sheet_id, before0, count);
                });
                out?
            };

            // Arrow insert (truth) + undo op.
            self.engine.ensure_arrow_sheet(sheet);
            if let Some(asheet) = self.engine.arrow_sheets.sheet_mut(sheet) {
                asheet.insert_rows(before0 as usize, count as usize);
            }
            self.engine
                .shift_row_visibility_insert(sheet_id, before0, count);
            if let Some(undo_ptr) = self.arrow_undo {
                unsafe { &mut *undo_ptr }.record_insert_rows(sheet_id, before0, count);
            }
            Ok(summary)
        } else {
            self.engine.insert_rows(sheet, before, count)
        }
    }

    #[inline]
    pub fn delete_rows(
        &mut self,
        sheet: &str,
        start: u32,
        count: u32,
    ) -> Result<crate::engine::ShiftSummary, crate::engine::EditorError> {
        if self.atomic_policy {
            return Err(crate::engine::EditorError::TransactionUnsupported {
                reason:
                    "delete_rows is not supported inside atomic actions (conservative rollback policy)"
                        .to_string(),
            });
        }
        self.engine.delete_rows(sheet, start, count)
    }

    #[inline]
    pub fn insert_columns(
        &mut self,
        sheet: &str,
        before: u32,
        count: u32,
    ) -> Result<crate::engine::ShiftSummary, crate::engine::EditorError> {
        if self.log.is_some() {
            let Some(log_ptr) = self.log else {
                return Err(crate::engine::EditorError::TransactionFailed {
                    reason: "action_atomic: missing ChangeLog".to_string(),
                });
            };

            let sheet_id = self.engine.graph.sheet_id_mut(sheet);
            let before0 = before.saturating_sub(1);
            let op = StructuralOp::InsertColumns {
                sheet_id,
                before: before0,
                count,
            };
            self.engine.demote_spans_for_structural_op(
                op,
                Engine::<R>::structural_col_region(sheet_id, before0),
            )?;

            let summary = {
                let log = unsafe { &mut *log_ptr };
                let mut out: Result<crate::engine::ShiftSummary, crate::engine::EditorError> =
                    Ok(crate::engine::ShiftSummary::default());
                self.engine.edit_with_logger(log, |editor| {
                    out = editor.insert_columns(sheet_id, before0, count);
                });
                out?
            };

            self.engine.ensure_arrow_sheet(sheet);
            if let Some(asheet) = self.engine.arrow_sheets.sheet_mut(sheet) {
                asheet.insert_columns(before0 as usize, count as usize);
            }
            if let Some(undo_ptr) = self.arrow_undo {
                unsafe { &mut *undo_ptr }.record_insert_cols(sheet_id, before0, count);
            }
            Ok(summary)
        } else {
            self.engine.insert_columns(sheet, before, count)
        }
    }

    #[inline]
    pub fn delete_columns(
        &mut self,
        sheet: &str,
        start: u32,
        count: u32,
    ) -> Result<crate::engine::ShiftSummary, crate::engine::EditorError> {
        if self.atomic_policy {
            return Err(crate::engine::EditorError::TransactionUnsupported {
                reason:
                    "delete_columns is not supported inside atomic actions (conservative rollback policy)"
                        .to_string(),
            });
        }
        self.engine.delete_columns(sheet, start, count)
    }

    /// Start an action from within an action.
    ///
    /// Nested actions are currently disallowed (ticket 614), so this will return a
    /// `EditorError::TransactionFailed` while an outer action is active.
    #[inline]
    pub fn action<T>(
        &mut self,
        name: impl AsRef<str>,
        f: impl FnOnce(&mut EngineAction<'_, R>) -> Result<T, crate::engine::EditorError>,
    ) -> Result<T, crate::engine::EditorError> {
        self.engine.action(name, f)
    }
}

struct ActionDepthGuard<'a, R> {
    engine: *mut Engine<R>,
    _marker: std::marker::PhantomData<&'a mut Engine<R>>,
}

impl<'a, R> Drop for ActionDepthGuard<'a, R> {
    fn drop(&mut self) {
        // Safety: the guard is created from a unique `&mut Engine` borrow and lives no longer
        // than the surrounding `Engine::action` call.
        unsafe {
            let e = &mut *self.engine;
            e.action_depth = e.action_depth.saturating_sub(1);
        }
    }
}

#[derive(Default)]
struct SourceCache {
    scalars: FxHashMap<(String, Option<u64>), LiteralValue>,
    tables: FxHashMap<(String, Option<u64>), Arc<dyn crate::traits::Table>>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
struct VisibilityMaskCacheKey {
    sheet_id: SheetId,
    start_row0: u32,
    end_row0: u32,
    mode: VisibilityMaskMode,
    version: u64,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum StructuralScope {
    Cell { sheet: SheetId, row: u32, col: u32 },
    Region(Region),
    Sheet(SheetId),
    RemovedSheet(SheetId),
    AllSheets,
}

struct SourceCacheSession {
    cache: Arc<std::sync::RwLock<SourceCache>>,
}

impl Drop for SourceCacheSession {
    fn drop(&mut self) {
        if let Ok(mut g) = self.cache.write() {
            *g = SourceCache::default();
        }
    }
}

#[derive(Debug)]
pub struct EvalResult {
    pub computed_vertices: usize,
    pub cycle_errors: usize,
    pub elapsed: std::time::Duration,
}

/// Read-only engine counters used by benchmark/instrumentation tooling.
///
/// These counters are deliberately observational: collecting them must not mutate engine state or
/// alter formula evaluation semantics.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct EngineBaselineStats {
    pub graph_vertex_count: usize,
    pub graph_formula_vertex_count: usize,
    pub graph_edge_count: usize,
    pub dirty_vertex_count: usize,
    pub evaluation_vertex_count: usize,
    pub formula_ast_root_count: usize,
    pub formula_ast_node_count: usize,
    pub staged_formula_count: usize,
    pub formula_plane_active_span_count: usize,
    pub formula_plane_producer_result_entries: usize,
    pub formula_plane_consumer_read_entries: usize,
    /// Number of spans demoted to legacy because a member participated in a
    /// statically-cyclic SCC (gotcha G8, refs #112).
    pub formula_plane_cycle_member_span_demotions: u64,
}

#[derive(Debug, Clone, Default)]
pub struct VirtualDepTelemetry {
    pub candidate_vertices_total: usize,
    pub vdeps_vertices_total: usize,
    pub vdeps_edges_total: usize,
    pub builder_elapsed_ms_total: u128,
    pub schedule_virtual_passes: usize,
    pub schedule_static_passes: usize,
    pub schedule_cache_hits: usize,
    pub schedule_cache_misses: usize,
    pub reused_schedule_vertices_total: usize,
    pub replan_iterations: usize,
    pub changed_vdeps_total: usize,
    pub bailout_reason: Option<&'static str>,
    pub fallback_mode_activations: u64,
}

/// Per-recalc telemetry for SCC evaluation under `CycleDetection::Runtime`
/// (spec `formualizer-cycle-semantics-spec.md` §10).
///
/// Collection is unconditional: SCC tasks are rare relative to ordinary
/// vertex evaluation and the counters are a handful of integer adds per
/// task, so no config flag gates them (unlike [`VirtualDepTelemetry`],
/// which pays per-schedule costs). Counters reset at the start of every
/// evaluation request.
#[derive(Debug, Clone, Default, PartialEq)]
pub struct CycleTelemetry {
    /// SCC tasks executed (static SCCs that reached Runtime evaluation).
    pub static_sccs: usize,
    /// SCC tasks whose live subgraph was acyclic — values produced.
    pub phantom_sccs: usize,
    /// Distinct live cycles witnessed across all SCC tasks.
    pub live_cycles_witnessed: usize,
    /// Cells stamped `#CIRC!` by Runtime SCC tasks.
    pub circ_cells_stamped: usize,
    /// Evaluation sweeps over (subsets of) SCC members, totalled across tasks
    /// (pass 1 included).
    pub settle_passes_total: usize,
    /// Largest pass count any single SCC task needed.
    pub max_passes_single_scc: usize,
    /// SCC tasks that entered iterative calculation (`CyclePolicy::Iterate`
    /// with a witnessed live cycle). RFC #113, Stage 3.
    pub iterated_sccs: usize,
    /// Iterating SCC tasks that stopped because every member passed the
    /// spec-§6 convergence test.
    pub converged_sccs: usize,
    /// SCC tasks that stopped at a pass cap. Under `CyclePolicy::Iterate`
    /// this is the Excel `max_iterations` cap (NOT an error — last values
    /// are kept; includes the no-convergence-test `max_iterations: 1`
    /// contract). Under `CyclePolicy::Error` it is the defensive acyclic
    /// settle cap (|SCC| + 2), which only a bug can hit.
    pub capped_sccs: usize,
    /// Largest `|Δ|` observed in any member's final-pass convergence
    /// comparison across iterating SCC tasks (numeric-class members only).
    /// `0.0` when no comparison ran (e.g. `max_iterations: 1`).
    pub max_abs_delta_at_stop: f64,
    /// Identical-bit NaN vs NaN member comparisons that were treated as
    /// converged (spec §6 NaN rule).
    pub nan_converged: usize,
    /// Total wall-clock time spent inside Runtime SCC tasks.
    pub elapsed_ms: u128,
}

#[derive(Debug, Clone, Copy)]
struct ScheduleBuildMeta {
    candidate_vertices: usize,
    vdeps_vertices: usize,
    vdeps_edges: usize,
    builder_elapsed_ms: u128,
    used_virtual_schedule: bool,
    schedule_cache_hit: bool,
    schedule_cache_eligible: bool,
}

#[derive(Debug, Clone)]
struct CachedScheduleEntry {
    topology_epoch: u64,
    candidate_vertices: Vec<VertexId>,
    schedule: crate::engine::scheduler::Schedule,
}

type ScheduleBuildOutput = (
    crate::engine::scheduler::Schedule,
    FxHashMap<VertexId, Vec<VertexId>>,
    ScheduleBuildMeta,
);

/// Cached evaluation schedule that can be replayed across multiple recalculations.
#[derive(Debug)]
pub struct RecalcPlan {
    schedule: crate::engine::Schedule,
    has_dynamic_refs: bool,
}

impl RecalcPlan {
    pub fn layer_count(&self) -> usize {
        self.schedule.layers.len()
    }

    pub fn has_dynamic_refs(&self) -> bool {
        self.has_dynamic_refs
    }
}

#[cfg(test)]
pub(crate) mod criteria_mask_test_hooks {
    use std::cell::Cell;

    thread_local! {
        static TEXT_SEGMENTS_TOTAL: Cell<usize> = const { Cell::new(0) };
        static TEXT_SEGMENTS_ALL_NULL: Cell<usize> = const { Cell::new(0) };
    }

    pub fn reset_text_segment_counters() {
        TEXT_SEGMENTS_TOTAL.with(|c| c.set(0));
        TEXT_SEGMENTS_ALL_NULL.with(|c| c.set(0));
    }

    pub fn text_segment_counters() -> (usize, usize) {
        let a = TEXT_SEGMENTS_TOTAL.with(|c| c.get());
        let b = TEXT_SEGMENTS_ALL_NULL.with(|c| c.get());
        (a, b)
    }

    pub(crate) fn inc_total() {
        TEXT_SEGMENTS_TOTAL.with(|c| c.set(c.get() + 1));
    }
    pub(crate) fn inc_all_null() {
        TEXT_SEGMENTS_ALL_NULL.with(|c| c.set(c.get() + 1));
    }
}

#[cfg(test)]
pub(crate) mod visibility_mask_test_hooks {
    use std::cell::Cell;

    thread_local! {
        static HITS: Cell<usize> = const { Cell::new(0) };
        static MISSES: Cell<usize> = const { Cell::new(0) };
        static EVICTIONS: Cell<usize> = const { Cell::new(0) };
    }

    pub fn reset() {
        HITS.with(|c| c.set(0));
        MISSES.with(|c| c.set(0));
        EVICTIONS.with(|c| c.set(0));
    }

    pub fn counters() -> (usize, usize, usize) {
        let hits = HITS.with(|c| c.get());
        let misses = MISSES.with(|c| c.get());
        let evictions = EVICTIONS.with(|c| c.get());
        (hits, misses, evictions)
    }

    pub(crate) fn inc_hit() {
        HITS.with(|c| c.set(c.get() + 1));
    }

    pub(crate) fn inc_miss() {
        MISSES.with(|c| c.set(c.get() + 1));
    }

    pub(crate) fn inc_eviction() {
        EVICTIONS.with(|c| c.set(c.get() + 1));
    }
}

fn compute_criteria_mask(
    view: &RangeView<'_>,
    col_in_view: usize,
    pred: &crate::args::CriteriaPredicate,
) -> Option<std::sync::Arc<arrow_array::BooleanArray>> {
    use crate::compute_prelude::{boolean, cmp, concat_arrays};
    use arrow::compute::kernels::comparison::{ilike, nilike};
    use arrow_array::{
        Array as _, ArrayRef, BooleanArray, Float64Array, StringArray, builder::BooleanBuilder,
    };

    // Helper: apply a numeric predicate to a single Float64Array chunk
    fn apply_numeric_pred(
        chunk: &Float64Array,
        pred: &crate::args::CriteriaPredicate,
    ) -> Option<BooleanArray> {
        match pred {
            crate::args::CriteriaPredicate::Gt(n) => {
                cmp::gt(chunk, &Float64Array::new_scalar(*n)).ok()
            }
            crate::args::CriteriaPredicate::Ge(n) => {
                cmp::gt_eq(chunk, &Float64Array::new_scalar(*n)).ok()
            }
            crate::args::CriteriaPredicate::Lt(n) => {
                cmp::lt(chunk, &Float64Array::new_scalar(*n)).ok()
            }
            crate::args::CriteriaPredicate::Le(n) => {
                cmp::lt_eq(chunk, &Float64Array::new_scalar(*n)).ok()
            }
            crate::args::CriteriaPredicate::Eq(v) => match v {
                formualizer_common::LiteralValue::Number(x) => {
                    cmp::eq(chunk, &Float64Array::new_scalar(*x)).ok()
                }
                formualizer_common::LiteralValue::Int(i) => {
                    cmp::eq(chunk, &Float64Array::new_scalar(*i as f64)).ok()
                }
                _ => None,
            },
            crate::args::CriteriaPredicate::Ne(v) => match v {
                formualizer_common::LiteralValue::Number(x) => {
                    cmp::neq(chunk, &Float64Array::new_scalar(*x)).ok()
                }
                formualizer_common::LiteralValue::Int(i) => {
                    cmp::neq(chunk, &Float64Array::new_scalar(*i as f64)).ok()
                }
                _ => None,
            },
            _ => None,
        }
    }

    // Check if this is a numeric predicate that can be applied per-chunk
    let is_numeric_pred = matches!(
        pred,
        crate::args::CriteriaPredicate::Gt(_)
            | crate::args::CriteriaPredicate::Ge(_)
            | crate::args::CriteriaPredicate::Lt(_)
            | crate::args::CriteriaPredicate::Le(_)
            | crate::args::CriteriaPredicate::Eq(formualizer_common::LiteralValue::Number(_))
            | crate::args::CriteriaPredicate::Eq(formualizer_common::LiteralValue::Int(_))
            | crate::args::CriteriaPredicate::Ne(formualizer_common::LiteralValue::Number(_))
            | crate::args::CriteriaPredicate::Ne(formualizer_common::LiteralValue::Int(_))
    );

    // OPTIMIZED PATH: For numeric predicates, apply per-chunk and concatenate boolean masks.
    // This avoids materializing the full numeric column (64-bit per element) and instead
    // concatenates boolean masks (1-bit per element) - a 64x memory reduction.
    if is_numeric_pred {
        let mut bool_parts: Vec<BooleanArray> = Vec::new();
        for res in view.numbers_slices() {
            let (_rs, _rl, cols_seg) = res.ok()?;
            if col_in_view < cols_seg.len() {
                let chunk = cols_seg[col_in_view].as_ref();
                let mask = apply_numeric_pred(chunk, pred)?;
                bool_parts.push(mask);
            }
        }

        if bool_parts.is_empty() {
            return None;
        } else if bool_parts.len() == 1 {
            return Some(std::sync::Arc::new(bool_parts.remove(0)));
        } else {
            // Concatenate boolean masks (much cheaper than concatenating Float64 arrays)
            let anys: Vec<&dyn arrow_array::Array> = bool_parts
                .iter()
                .map(|a| a as &dyn arrow_array::Array)
                .collect();
            let conc: ArrayRef = concat_arrays(&anys).ok()?;
            let ba = conc.as_any().downcast_ref::<BooleanArray>()?.clone();
            return Some(std::sync::Arc::new(ba));
        }
    }

    // TEXT PATH: build masks per row-chunk using lowered text slices.
    // This avoids concatenating full-string columns just to compute a boolean mask.
    let (text_kind, text_pat, empty_special) = match pred {
        crate::args::CriteriaPredicate::Eq(formualizer_common::LiteralValue::Text(t)) => {
            (0u8, t.to_lowercase(), t.is_empty())
        }
        crate::args::CriteriaPredicate::Ne(formualizer_common::LiteralValue::Text(t)) => {
            (1u8, t.to_lowercase(), false)
        }
        crate::args::CriteriaPredicate::TextLike {
            pattern,
            case_insensitive,
        } => {
            let p = if *case_insensitive {
                pattern.to_lowercase()
            } else {
                pattern.clone()
            };
            (2u8, p.replace('*', "%").replace('?', "_"), false)
        }
        _ => return None,
    };

    let ne_matches_blank = text_kind == 1 && !text_pat.is_empty();
    let pat = StringArray::new_scalar(text_pat);
    let mut bool_parts: Vec<BooleanArray> = Vec::new();

    for res in view.iter_row_chunks() {
        let cs = res.ok()?;
        if cs.row_len == 0 {
            continue;
        }
        #[cfg(test)]
        criteria_mask_test_hooks::inc_total();

        let slices = view.slice_lowered_text(cs.row_start, cs.row_len);
        if col_in_view >= slices.len() {
            return None;
        }

        let seg_opt = slices[col_in_view].as_ref().map(|a| a.as_ref());
        let seg = match seg_opt {
            Some(s) => s,
            None => {
                #[cfg(test)]
                criteria_mask_test_hooks::inc_all_null();
                if (text_kind == 0 && empty_special) || ne_matches_blank {
                    // Eq("") treats nulls (Empty) as equal.
                    let mut bb = BooleanBuilder::with_capacity(cs.row_len);
                    bb.append_n(cs.row_len, true);
                    bool_parts.push(bb.finish());
                } else {
                    // For non-empty patterns, ilike/nilike return null on null inputs.
                    bool_parts.push(BooleanArray::new_null(cs.row_len));
                }
                continue;
            }
        };

        let seg_sa = seg.as_any().downcast_ref::<StringArray>()?;
        let mut m = match text_kind {
            0 => ilike(seg_sa, &pat).ok()?,
            1 => nilike(seg_sa, &pat).ok()?,
            2 => ilike(seg_sa, &pat).ok()?,
            _ => return None,
        };

        // Only fold blank/Empty (null) cells into the mask when the segment
        // actually contains any. The null-fill loop + or_kleene are pure
        // overhead on blank-free chunks, so a `<>text` (or `=""`) aggregation
        // over a column with no blanks stays fully vectorized on the ilike/
        // nilike result.
        if ((text_kind == 0 && empty_special) || ne_matches_blank) && seg_sa.null_count() > 0 {
            // Treat nulls as equal to empty string
            let mut bb = BooleanBuilder::with_capacity(seg_sa.len());
            for i in 0..seg_sa.len() {
                bb.append_value(seg_sa.is_null(i));
            }
            let nulls = bb.finish();
            m = boolean::or_kleene(&m, &nulls).ok()?;
        }

        bool_parts.push(m);
    }

    if bool_parts.is_empty() {
        None
    } else if bool_parts.len() == 1 {
        Some(std::sync::Arc::new(bool_parts.remove(0)))
    } else {
        let anys: Vec<&dyn arrow_array::Array> = bool_parts
            .iter()
            .map(|a| a as &dyn arrow_array::Array)
            .collect();
        let conc: ArrayRef = concat_arrays(&anys).ok()?;
        let ba = conc.as_any().downcast_ref::<BooleanArray>()?.clone();
        Some(std::sync::Arc::new(ba))
    }
}

#[derive(Debug, Clone)]
pub struct LayerInfo {
    pub vertex_count: usize,
    pub parallel_eligible: bool,
    pub sample_cells: Vec<String>, // Sample of up to 5 cell addresses
}

#[derive(Debug, Clone)]
pub struct EvalPlan {
    pub total_vertices_to_evaluate: usize,
    pub layers: Vec<LayerInfo>,
    pub cycles_detected: usize,
    pub dirty_count: usize,
    pub volatile_count: usize,
    pub parallel_enabled: bool,
    pub estimated_parallel_layers: usize,
    pub target_cells: Vec<String>,
}

impl<R> Engine<R>
where
    R: EvaluationContext,
{
    /// # Panics
    /// Panics when `config.cycle` is invalid ([`CycleConfig::validate`],
    /// spec §2): `Iterate` with `detection: Static`, `max_iterations == 0`,
    /// or a negative/non-finite `max_change`. `EvalConfig::with_cycle`
    /// rejects these at build; this re-validates configs assembled via
    /// struct literals.
    pub fn new(resolver: R, config: EvalConfig) -> Self {
        if let Err(msg) = config.cycle.validate() {
            panic!("invalid CycleConfig: {msg}");
        }
        crate::builtins::load_builtins();

        let clock = config.deterministic_mode.build_clock().unwrap_or_else(|_| {
            #[cfg(feature = "system-clock")]
            {
                Arc::new(crate::timezone::SystemClock::new(
                    crate::timezone::TimeZoneSpec::default(),
                ))
            }
            #[cfg(not(feature = "system-clock"))]
            {
                Arc::new(crate::timezone::FixedClock::new(
                    chrono::DateTime::UNIX_EPOCH,
                    crate::timezone::TimeZoneSpec::Utc,
                ))
            }
        });

        // Initialize thread pool based on config
        let thread_pool = if config.enable_parallel {
            let mut builder = ThreadPoolBuilder::new();
            if let Some(max_threads) = config.max_threads {
                builder = builder.num_threads(max_threads);
            }

            match builder.build() {
                Ok(pool) => Some(Arc::new(pool)),
                Err(_) => {
                    // Fall back to sequential evaluation if thread pool creation fails
                    None
                }
            }
        } else {
            None
        };

        let lookup_cache_max_bytes = config.lookup_index_cache_max_bytes;
        let mut engine = Self {
            graph: DependencyGraph::new_with_config(config.clone()),
            resolver,
            config,
            workbook_load_limits: crate::engine::WorkbookLoadLimits::default(),
            clock: crate::timezone::SnapshotClock::new(clock),
            thread_pool,
            recalc_epoch: 0,
            snapshot_id: std::sync::atomic::AtomicU64::new(1),
            topology_epoch: 0,
            cached_static_schedule: None,
            spill_mgr: ShimSpillManager::default(),
            arrow_sheets: SheetStore::default(),
            has_edited: false,
            overlay_compactions: 0,
            computed_overlay_bytes_estimate: 0,
            computed_overlay_mirroring_disabled: false,
            force_materialize_range_views: false,
            row_bounds_cache: std::sync::RwLock::new(None),
            used_axis_bounds_cache: std::sync::RwLock::new(None),
            lookup_index_cache: LookupIndexCache::new(lookup_cache_max_bytes),
            source_cache: Arc::new(std::sync::RwLock::new(SourceCache::default())),
            staged_formulas: std::collections::HashMap::new(),
            row_visibility: FxHashMap::default(),
            row_visibility_mask_cache: std::sync::RwLock::new(FxHashMap::default()),
            formula_parse_diagnostics: Vec::new(),
            last_formula_ingest_report: None,
            formula_ingest_report_total: FormulaIngestReport::default(),
            formula_plane_cycle_member_span_demotions: 0,
            formula_plane_capacity_bailouts: 0,
            active_cancel_flag: None,
            action_depth: 0,
            last_virtual_dep_telemetry: VirtualDepTelemetry::default(),
            virtual_dep_fallback_activations: 0,
            last_cycle_telemetry: CycleTelemetry::default(),
            pending_iterative_redirty: Vec::new(),
            iterative_state_values: FxHashMap::default(),
            formula_plane_indexes_epoch_seen: 0,
            #[cfg(test)]
            last_formula_plane_span_eval_report: None,
        };
        // Phase 1 (ticket 610): Arrow-truth is the only supported mode.
        engine.config.arrow_storage_enabled = true;
        engine.config.delta_overlay_enabled = true;
        engine.config.write_formula_overlay_enabled = true;
        let default_sheet = engine.graph.default_sheet_name().to_string();
        engine.ensure_arrow_sheet(&default_sheet);
        engine
    }

    /// Create an Engine with a custom thread pool (for shared thread pool scenarios)
    ///
    /// # Panics
    /// Panics when `config.cycle` is invalid, exactly like [`Engine::new`].
    pub fn with_thread_pool(
        resolver: R,
        config: EvalConfig,
        thread_pool: Arc<rayon::ThreadPool>,
    ) -> Self {
        if let Err(msg) = config.cycle.validate() {
            panic!("invalid CycleConfig: {msg}");
        }
        crate::builtins::load_builtins();
        let clock = config.deterministic_mode.build_clock().unwrap_or_else(|_| {
            #[cfg(feature = "system-clock")]
            {
                Arc::new(crate::timezone::SystemClock::new(
                    crate::timezone::TimeZoneSpec::default(),
                ))
            }
            #[cfg(not(feature = "system-clock"))]
            {
                Arc::new(crate::timezone::FixedClock::new(
                    chrono::DateTime::UNIX_EPOCH,
                    crate::timezone::TimeZoneSpec::Utc,
                ))
            }
        });
        let lookup_cache_max_bytes = config.lookup_index_cache_max_bytes;
        let mut engine = Self {
            graph: DependencyGraph::new_with_config(config.clone()),
            resolver,
            config,
            workbook_load_limits: crate::engine::WorkbookLoadLimits::default(),
            clock: crate::timezone::SnapshotClock::new(clock),
            thread_pool: Some(thread_pool),
            recalc_epoch: 0,
            snapshot_id: std::sync::atomic::AtomicU64::new(1),
            topology_epoch: 0,
            cached_static_schedule: None,
            spill_mgr: ShimSpillManager::default(),
            arrow_sheets: SheetStore::default(),
            has_edited: false,
            overlay_compactions: 0,
            computed_overlay_bytes_estimate: 0,
            computed_overlay_mirroring_disabled: false,
            force_materialize_range_views: false,
            row_bounds_cache: std::sync::RwLock::new(None),
            used_axis_bounds_cache: std::sync::RwLock::new(None),
            lookup_index_cache: LookupIndexCache::new(lookup_cache_max_bytes),
            source_cache: Arc::new(std::sync::RwLock::new(SourceCache::default())),
            staged_formulas: std::collections::HashMap::new(),
            row_visibility: FxHashMap::default(),
            row_visibility_mask_cache: std::sync::RwLock::new(FxHashMap::default()),
            formula_parse_diagnostics: Vec::new(),
            last_formula_ingest_report: None,
            formula_ingest_report_total: FormulaIngestReport::default(),
            formula_plane_cycle_member_span_demotions: 0,
            formula_plane_capacity_bailouts: 0,
            active_cancel_flag: None,
            action_depth: 0,
            last_virtual_dep_telemetry: VirtualDepTelemetry::default(),
            virtual_dep_fallback_activations: 0,
            last_cycle_telemetry: CycleTelemetry::default(),
            pending_iterative_redirty: Vec::new(),
            iterative_state_values: FxHashMap::default(),
            formula_plane_indexes_epoch_seen: 0,
            #[cfg(test)]
            last_formula_plane_span_eval_report: None,
        };
        // Phase 1 (ticket 610): Arrow-truth is the only supported mode.
        engine.config.arrow_storage_enabled = true;
        engine.config.delta_overlay_enabled = true;
        engine.config.write_formula_overlay_enabled = true;
        let default_sheet = engine.graph.default_sheet_name().to_string();
        engine.ensure_arrow_sheet(&default_sheet);
        engine
    }

    pub fn workbook_load_limits(&self) -> &crate::engine::WorkbookLoadLimits {
        &self.workbook_load_limits
    }

    pub fn set_workbook_load_limits(&mut self, limits: crate::engine::WorkbookLoadLimits) {
        self.workbook_load_limits = limits;
    }

    fn clear_source_cache(&self) {
        if let Ok(mut g) = self.source_cache.write() {
            *g = SourceCache::default();
        }
    }

    pub fn last_virtual_dep_telemetry(&self) -> &VirtualDepTelemetry {
        &self.last_virtual_dep_telemetry
    }

    /// Telemetry from Runtime SCC evaluation during the most recent
    /// evaluation request (always default-zero under `CycleDetection::Static`
    /// or when `enable_virtual_dep_telemetry` is off).
    pub fn last_cycle_telemetry(&self) -> &CycleTelemetry {
        &self.last_cycle_telemetry
    }

    /// Begin a new evaluation request: reset per-recalc cycle telemetry and
    /// take the per-recalc volatile clock sample. Called at the start of
    /// every evaluation request that walks schedule units.
    fn begin_evaluation_request(&mut self) {
        self.last_cycle_telemetry = CycleTelemetry::default();
        // Defensive: consumed at the end of the previous request; a request
        // that errored out mid-walk must not leak its members into this one.
        self.pending_iterative_redirty.clear();
        // Spec §7.11: NOW()/TODAY() sample the clock ONCE per recalc; every
        // read within this request (including SCC iteration passes) observes
        // this sample.
        self.clock.refresh();
    }

    /// End-of-recalc redirty: volatile vertices (as always) plus members of
    /// SCCs that iterated this recalc (`CyclePolicy::Iterate`), so circular
    /// cells re-evaluate on every recalc exactly like Excel's iterative
    /// calculation (spec §4 persistence / §7.6 accumulator / §7.11 volatile
    /// redirty). Replaces the bare `graph.redirty_volatiles()` call at every
    /// evaluation-flow exit; must run AFTER the flow's `clear_dirty_flags`.
    fn redirty_for_next_recalc(&mut self) {
        self.graph.redirty_volatiles();
        let pending = std::mem::take(&mut self.pending_iterative_redirty);
        // Refresh the §4-persistence snapshot: these final values survive
        // structural edits that clear the computed overlay (the only value
        // home in canonical mode) so the next SCC task can re-seed from them
        // (see `iterative_state_values`). Replaced wholesale each recalc —
        // when nothing iterates the map empties and stays free.
        self.iterative_state_values.clear();
        for &vertex in &pending {
            if !self.graph.vertex_exists(vertex) {
                continue;
            }
            if let Some(cell) = self.graph.get_cell_ref(vertex) {
                let sheet_name = self.graph.sheet_name(cell.sheet_id);
                if let Some(value) =
                    self.get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                    && !matches!(value, LiteralValue::Empty)
                {
                    self.iterative_state_values.insert(vertex, value);
                }
            }
        }
        if !pending.is_empty() {
            self.graph.redirty_iterative_members(&pending);
        }
    }

    pub fn virtual_dep_fallback_activations(&self) -> u64 {
        self.virtual_dep_fallback_activations
    }

    pub(crate) fn last_lookup_index_cache_report(&self) -> LookupIndexCacheReport {
        self.lookup_index_cache.report()
    }

    fn lookup_view_contains_volatile(&self, view: &RangeView<'_>, sheet_id: SheetId) -> bool {
        let start_row = view.start_row();
        let end_row = view.end_row();
        let start_col = view.start_col();
        let end_col = view.end_col();
        for row in start_row..=end_row {
            let Ok(row_u32) = u32::try_from(row) else {
                return true;
            };
            for col in start_col..=end_col {
                let Ok(col_u32) = u32::try_from(col) else {
                    return true;
                };
                let cell_ref = self
                    .graph
                    .make_cell_ref_internal(sheet_id, row_u32, col_u32);
                if let Some(vertex_id) = self.graph.get_vertex_id_for_address(&cell_ref)
                    && self.graph.is_volatile(*vertex_id)
                {
                    return true;
                }
            }
        }
        false
    }

    fn build_lookup_index_impl(
        &self,
        view: &RangeView<'_>,
        axis: LookupAxis,
    ) -> Option<Arc<LookupIndex>> {
        let (rows, cols) = view.dims();
        if rows == 0 || cols == 0 {
            self.lookup_index_cache.note_skipped_tiny();
            return None;
        }
        let len = match axis {
            LookupAxis::ColumnInView(col) => {
                if col >= cols {
                    self.lookup_index_cache.note_skipped_tiny();
                    return None;
                }
                rows
            }
            LookupAxis::RowInView(row) => {
                if row >= rows {
                    self.lookup_index_cache.note_skipped_tiny();
                    return None;
                }
                cols
            }
        };
        if len < 64 {
            self.lookup_index_cache.note_skipped_tiny();
            return None;
        }

        let sheet_id = self.graph.sheet_id(view.sheet_name())?;
        let key = LookupIndexKey {
            sheet_id,
            start_row: u32::try_from(view.start_row()).ok()?,
            start_col: u32::try_from(view.start_col()).ok()?,
            end_row: u32::try_from(view.end_row()).ok()?,
            end_col: u32::try_from(view.end_col()).ok()?,
            axis,
            snapshot_id: self.data_snapshot_id(),
        };
        if let Some(index) = self.lookup_index_cache.get(&key) {
            return Some(index);
        }
        if self
            .lookup_index_cache
            .would_exceed_cap(estimate_bytes(len, 0))
        {
            self.lookup_index_cache.note_skipped_cap();
            return None;
        }
        if !self.lookup_index_cache.should_build(key) {
            return None;
        }
        if self.lookup_index_cache.is_known_volatile(&key) {
            self.lookup_index_cache.note_skipped_volatile();
            return None;
        }
        if self.lookup_view_contains_volatile(view, sheet_id) {
            self.lookup_index_cache.note_volatile_key(key);
            self.lookup_index_cache.note_skipped_volatile();
            return None;
        }
        match LookupIndex::build(view, axis).ok()? {
            BuildOutcome::Built(index) => self.lookup_index_cache.insert_if_room(key, index),
            BuildOutcome::ErrorInLookupAxis => {
                self.lookup_index_cache.note_skipped_error();
                None
            }
            BuildOutcome::Degenerate => {
                self.lookup_index_cache.note_skipped_tiny();
                None
            }
        }
    }

    fn reset_virtual_dep_telemetry_if_disabled(&mut self) {
        if !self.config.enable_virtual_dep_telemetry {
            self.last_virtual_dep_telemetry = VirtualDepTelemetry {
                fallback_mode_activations: self.virtual_dep_fallback_activations,
                ..VirtualDepTelemetry::default()
            };
        }
    }

    fn source_cache_session(&self) -> SourceCacheSession {
        self.clear_source_cache();
        SourceCacheSession {
            cache: self.source_cache.clone(),
        }
    }

    fn resolve_source_scalar_cached(
        &self,
        name: &str,
        version: Option<u64>,
    ) -> Result<LiteralValue, ExcelError> {
        let key = (name.to_string(), version);
        if let Ok(mut g) = self.source_cache.write() {
            if let Some(v) = g.scalars.get(&key) {
                return Ok(v.clone());
            }

            let v = self.resolver.resolve_source_scalar(name).map_err(|err| {
                if matches!(err.kind, ExcelErrorKind::Name | ExcelErrorKind::NImpl) {
                    ExcelError::new(ExcelErrorKind::Ref)
                        .with_message(format!("Unresolved source scalar: {name}"))
                } else {
                    err
                }
            })?;
            g.scalars.insert(key, v.clone());
            Ok(v)
        } else {
            self.resolver.resolve_source_scalar(name).map_err(|err| {
                if matches!(err.kind, ExcelErrorKind::Name | ExcelErrorKind::NImpl) {
                    ExcelError::new(ExcelErrorKind::Ref)
                        .with_message(format!("Unresolved source scalar: {name}"))
                } else {
                    err
                }
            })
        }
    }

    fn resolve_source_table_cached(
        &self,
        name: &str,
        version: Option<u64>,
    ) -> Result<Arc<dyn crate::traits::Table>, ExcelError> {
        let key = (name.to_string(), version);
        if let Ok(mut g) = self.source_cache.write() {
            if let Some(t) = g.tables.get(&key) {
                return Ok(t.clone());
            }

            let t = self.resolver.resolve_source_table(name).map_err(|err| {
                if matches!(err.kind, ExcelErrorKind::Name | ExcelErrorKind::NImpl) {
                    ExcelError::new(ExcelErrorKind::Ref)
                        .with_message(format!("Unresolved source table: {name}"))
                } else {
                    err
                }
            })?;
            let t: Arc<dyn crate::traits::Table> = Arc::from(t);
            g.tables.insert(key, t.clone());
            Ok(t)
        } else {
            self.resolver
                .resolve_source_table(name)
                .map_err(|err| {
                    if matches!(err.kind, ExcelErrorKind::Name | ExcelErrorKind::NImpl) {
                        ExcelError::new(ExcelErrorKind::Ref)
                            .with_message(format!("Unresolved source table: {name}"))
                    } else {
                        err
                    }
                })
                .map(Arc::from)
        }
    }

    fn source_table_to_range_view(
        &self,
        table: &dyn crate::traits::Table,
        spec: &Option<formualizer_parse::parser::TableSpecifier>,
    ) -> Result<RangeView<'static>, ExcelError> {
        use formualizer_parse::parser::{SpecialItem, TableSpecifier};

        let owned = match spec {
            Some(TableSpecifier::Column(c)) => {
                let c = c.trim();
                if c == "@" || c.contains('[') || c.contains(']') || c.contains(',') {
                    return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                        "Complex structured references not yet supported".to_string(),
                    ));
                }
                table.get_column(c)?.materialise().into_owned()
            }
            Some(TableSpecifier::ColumnRange(start, end)) => {
                let cols = table.columns();
                let start = start.trim();
                let end = end.trim();
                let start_key = start.to_lowercase();
                let end_key = end.to_lowercase();
                let start_idx = cols.iter().position(|n| n.to_lowercase() == start_key);
                let end_idx = cols.iter().position(|n| n.to_lowercase() == end_key);
                if let (Some(mut si), Some(mut ei)) = (start_idx, end_idx) {
                    if si > ei {
                        std::mem::swap(&mut si, &mut ei);
                    }
                    let h = table.data_height();
                    let w = ei - si + 1;
                    let mut rows = vec![vec![LiteralValue::Empty; w]; h];
                    for (offset, ci) in (si..=ei).enumerate() {
                        let cname = &cols[ci];
                        let col_range = table.get_column(cname)?;
                        let (rh, _) = col_range.dimensions();
                        for (r, row) in rows.iter_mut().enumerate().take(h.min(rh)) {
                            row[offset] = col_range.get(r, 0)?;
                        }
                    }
                    rows
                } else {
                    return Err(ExcelError::new(ExcelErrorKind::Ref)
                        .with_message("Column range refers to unknown column(s)".to_string()));
                }
            }
            Some(TableSpecifier::SpecialItem(SpecialItem::Headers))
            | Some(TableSpecifier::Headers) => table
                .headers_row()
                .map(|r| r.materialise().into_owned())
                .unwrap_or_default(),
            Some(TableSpecifier::SpecialItem(SpecialItem::Totals))
            | Some(TableSpecifier::Totals) => table
                .totals_row()
                .map(|r| r.materialise().into_owned())
                .unwrap_or_default(),
            Some(TableSpecifier::SpecialItem(SpecialItem::Data)) | Some(TableSpecifier::Data) => {
                table
                    .data_body()
                    .map(|r| r.materialise().into_owned())
                    .unwrap_or_default()
            }
            Some(TableSpecifier::SpecialItem(SpecialItem::All)) | Some(TableSpecifier::All) => {
                let mut out: Vec<Vec<LiteralValue>> = Vec::new();
                if let Some(h) = table.headers_row() {
                    out.extend(h.iter_rows());
                }
                if let Some(body) = table.data_body() {
                    out.extend(body.iter_rows());
                }
                if let Some(tr) = table.totals_row() {
                    out.extend(tr.iter_rows());
                }
                out
            }
            Some(TableSpecifier::SpecialItem(SpecialItem::ThisRow)) => {
                return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                    "@ (This Row) requires table-aware context; not yet supported".to_string(),
                ));
            }
            Some(TableSpecifier::Row(_)) | Some(TableSpecifier::Combination(_)) => {
                return Err(ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("Complex structured references not yet supported".to_string()));
            }
            None => {
                return Err(ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("Table reference without specifier is unsupported".to_string()));
            }
        };

        Ok(RangeView::from_owned_rows(owned, self.config.date_system))
    }

    pub fn default_sheet_id(&self) -> SheetId {
        self.graph.default_sheet_id()
    }

    pub fn default_sheet_name(&self) -> &str {
        self.graph.default_sheet_name()
    }

    /// Update the workbook seed for deterministic RNGs in functions.
    pub fn set_workbook_seed(&mut self, seed: u64) {
        self.config.workbook_seed = seed;
    }

    /// Set the volatile level policy (Always/OnRecalc/OnOpen)
    pub fn set_volatile_level(&mut self, level: crate::traits::VolatileLevel) {
        self.config.volatile_level = level;
    }

    /// Enable/disable deterministic evaluation mode (fixed clock + timezone).
    pub fn set_deterministic_mode(
        &mut self,
        mode: crate::engine::DeterministicMode,
    ) -> Result<(), ExcelError> {
        let clock = mode.build_clock()?;
        self.config.deterministic_mode = mode;
        self.clock = crate::timezone::SnapshotClock::new(clock);
        Ok(())
    }

    /// Inject a custom [`ClockProvider`](crate::timezone::ClockProvider) for
    /// volatile date/time builtins (`NOW()`, `TODAY()`).
    ///
    /// The provider is the clock *source*; per spec §7.11 the engine samples
    /// it once at the start of every evaluation request and all reads within
    /// that recalc (including SCC iteration passes) observe the frozen
    /// sample.
    pub fn set_clock(&mut self, clock: Arc<dyn crate::timezone::ClockProvider>) {
        self.clock = crate::timezone::SnapshotClock::new(clock);
    }

    fn validate_deterministic_mode(&self) -> Result<(), ExcelError> {
        self.config.deterministic_mode.validate()
    }

    pub fn sheet_id(&self, name: &str) -> Option<SheetId> {
        self.graph.sheet_id(name)
    }

    pub fn sheet_id_mut(&mut self, name: &str) -> SheetId {
        self.add_sheet(name)
            .unwrap_or_else(|_| self.graph.sheet_id_mut(name))
    }

    pub fn sheet_name(&self, id: SheetId) -> &str {
        self.graph.sheet_name(id)
    }

    pub fn add_sheet(&mut self, name: &str) -> Result<SheetId, ExcelError> {
        let id = self.graph.add_sheet(name)?;
        self.ensure_arrow_sheet(name);
        // Adding a sheet does not invalidate existing SheetId-based FormulaPlane
        // spans. `graph.add_sheet` handles legacy orphan-healing for formulas
        // that were explicitly tombstoned for this sheet name; avoid a global
        // FormulaPlane demotion/dirty mark for unrelated spans.
        self.mark_topology_edited();
        Ok(id)
    }

    pub fn duplicate_sheet(&mut self, source: &str, new_name: &str) -> Result<SheetId, ExcelError> {
        let source_id = self.graph.sheet_id(source).ok_or_else(|| {
            ExcelError::new(ExcelErrorKind::Value).with_message("Source sheet does not exist")
        })?;
        // Materialize only spans on the source sheet so graph duplication sees
        // the formulas being copied. Spans on unrelated sheets remain active.
        self.demote_spans_preserving_computed_overlays(source_id, Region::whole_sheet(source_id))
            .map_err(Self::editor_error_to_excel)?;
        let new_id = self.graph.duplicate_sheet(source_id, new_name)?;

        if let Some(source_sheet) = self.arrow_sheets.sheet(source).cloned() {
            let mut copied_sheet = source_sheet;
            copied_sheet.name = Arc::<str>::from(new_name);
            self.arrow_sheets.sheets.push(copied_sheet);
        } else {
            self.ensure_arrow_sheet(new_name);
        }

        self.clear_all_computed_overlays();
        self.mark_all_formula_vertices_dirty();
        self.mark_topology_edited();
        Ok(new_id)
    }

    fn ensure_arrow_sheet(&mut self, name: &str) {
        if self.arrow_sheets.sheet(name).is_some() {
            return;
        }
        self.arrow_sheets
            .sheets
            .push(crate::arrow_store::ArrowSheet {
                name: std::sync::Arc::<str>::from(name),
                columns: Vec::new(),
                nrows: 0,
                chunk_starts: Vec::new(),
                chunk_rows: 32 * 1024,
            });
    }

    pub fn remove_sheet(&mut self, sheet_id: SheetId) -> Result<(), ExcelError> {
        let name = self.graph.sheet_name(sheet_id).to_string();
        // Removing a sheet only affects spans on that sheet and spans reading
        // from that sheet. Preserve spans on unrelated sheets so sheet
        // lifecycle operations do not collapse the whole FormulaPlane.
        self.demote_spans_preserving_computed_overlays(sheet_id, Region::whole_sheet(sheet_id))
            .map_err(Self::editor_error_to_excel)?;
        self.graph.remove_sheet(sheet_id)?;
        self.arrow_sheets.sheets.retain(|s| s.name.as_ref() != name);
        self.clear_all_computed_overlays();
        self.mark_all_formula_vertices_dirty();
        self.staged_formulas.remove(&name);
        if self.row_visibility.remove(&sheet_id).is_some() {
            self.invalidate_row_visibility_mask_cache();
        }
        self.record_formula_plane_structural_change(StructuralScope::RemovedSheet(sheet_id));
        self.mark_topology_edited();
        Ok(())
    }

    /// Helper to synchronize the Arrow-backed storage layer.
    fn rename_sheet_in_arrow_store(&mut self, target_name: &str, new_name: &str) -> bool {
        if let Some(asheet) = self
            .arrow_sheets
            .sheets
            .iter_mut()
            .find(|s| s.name.as_ref() == target_name)
        {
            asheet.name = std::sync::Arc::<str>::from(new_name);
            return true;
        }
        false
    }

    pub fn rename_sheet(&mut self, sheet_id: SheetId, new_name: &str) -> Result<(), ExcelError> {
        let old_name = self.graph.sheet_name(sheet_id).to_string();

        // Speculative Storage Update
        // Update name in storage FIRST so the Evaluator can find it during Graph rescue.
        self.rename_sheet_in_arrow_store(&old_name, new_name);

        // Graph Update (Metadata + Rescue Logic)
        match self.graph.rename_sheet(sheet_id, new_name) {
            Ok(_) => {
                self.rename_staged_formula_sheet(&old_name, new_name);
                // Success! Invalidate cache for the moved sheet
                let sheet_vertices: Vec<VertexId> =
                    self.graph.vertices_in_sheet(sheet_id).collect();
                for v_id in sheet_vertices {
                    self.graph.mark_vertex_dirty(v_id);
                }
                // Sheet rename is metadata-only and preserves SheetId. References resolve by
                // SheetId, so no FormulaPlane changed region is required. Removing this avoids
                // re-evaluating every span that reads the renamed sheet.
                self.mark_topology_edited();
                Ok(())
            }
            Err(e) => {
                // ROLLBACK: Revert storage if graph rejected the name
                self.rename_sheet_in_arrow_store(new_name, &old_name);
                Err(e)
            }
        }
    }

    pub fn named_ranges_iter(
        &self,
    ) -> impl Iterator<Item = (&String, &crate::engine::named_range::NamedRange)> {
        self.graph.named_ranges_iter()
    }

    pub fn sheet_named_ranges_iter(
        &self,
    ) -> impl Iterator<Item = (&(SheetId, String), &crate::engine::named_range::NamedRange)> {
        self.graph.sheet_named_ranges_iter()
    }

    pub fn resolve_name_entry(
        &self,
        name: &str,
        current_sheet: SheetId,
    ) -> Option<&crate::engine::named_range::NamedRange> {
        self.graph.resolve_name_entry(name, current_sheet)
    }

    pub fn named_ranges_snapshot(&self) -> Vec<crate::engine::named_range::NamedRangeSnapshot> {
        let mut out: Vec<crate::engine::named_range::NamedRangeSnapshot> = Vec::new();

        for (name, named) in self.graph.named_ranges_iter() {
            out.push(crate::engine::named_range::NamedRangeSnapshot {
                name: name.clone(),
                scope: NameScope::Workbook,
                definition: named.definition.clone(),
            });
        }

        for ((sheet_id, name), named) in self.graph.sheet_named_ranges_iter() {
            out.push(crate::engine::named_range::NamedRangeSnapshot {
                name: name.clone(),
                scope: NameScope::Sheet(*sheet_id),
                definition: named.definition.clone(),
            });
        }

        out.sort_by(|a, b| {
            let a_scope = match a.scope {
                NameScope::Workbook => (0u8, 0u32),
                NameScope::Sheet(id) => (1u8, u32::from(id)),
            };
            let b_scope = match b.scope {
                NameScope::Workbook => (0u8, 0u32),
                NameScope::Sheet(id) => (1u8, u32::from(id)),
            };
            a_scope.cmp(&b_scope).then_with(|| a.name.cmp(&b.name))
        });

        out
    }

    pub fn named_ranges_snapshot_for_sheet(
        &self,
        sheet_id: SheetId,
    ) -> Vec<crate::engine::named_range::NamedRangeSnapshot> {
        self.named_ranges_snapshot()
            .into_iter()
            .filter(|entry| match entry.scope {
                NameScope::Workbook => true,
                NameScope::Sheet(id) => id == sheet_id,
            })
            .collect()
    }

    pub fn define_name(
        &mut self,
        name: &str,
        definition: NamedDefinition,
        scope: NameScope,
    ) -> Result<(), ExcelError> {
        // A new define can flip resolution for spans that previously resolved
        // the same name through another scope (e.g. a sheet-scoped name
        // shadowing a workbook-scoped one). Demote those spans BEFORE the
        // registry changes so their cells re-ingest and re-resolve through
        // the normal legacy path.
        self.invalidate_formula_plane_spans_for_name(name)?;
        self.graph.define_name(name, definition, scope)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        self.mark_topology_edited();
        Ok(())
    }

    pub fn update_name(
        &mut self,
        name: &str,
        definition: NamedDefinition,
        scope: NameScope,
    ) -> Result<(), ExcelError> {
        // Demote name-dependent spans BEFORE the registry update: the demoted
        // cells re-materialize as legacy vertices attached to the name vertex
        // (via their resolved-name dep plans), so the registry update's
        // dependent dirtying reaches them exactly like long-lived legacy
        // formulas.
        self.invalidate_formula_plane_spans_for_name(name)?;
        self.graph.update_name(name, definition, scope)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        self.mark_topology_edited();
        Ok(())
    }

    pub fn delete_name(&mut self, name: &str, scope: NameScope) -> Result<(), ExcelError> {
        // Demote first (see update_name): the demoted legacy vertices become
        // dependents of the name vertex, so delete_name dirties them and they
        // re-evaluate to #NAME? exactly as legacy formulas do.
        self.invalidate_formula_plane_spans_for_name(name)?;
        self.graph.delete_name(name, scope)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        self.mark_topology_edited();
        Ok(())
    }

    /// Demote every FormulaPlane span whose ingest-time read projections
    /// resolved `name` (any scope; see the FormulaPlane name-dependents map
    /// for the conservative keying contract). Demotion materializes the span
    /// placements as legacy graph formulas through the existing demotion
    /// machinery, preserving computed values; the subsequent registry change
    /// then dirties them through the legacy name-dependents path.
    fn invalidate_formula_plane_spans_for_name(&mut self, name: &str) -> Result<(), ExcelError> {
        if self.config.formula_plane_mode == FormulaPlaneMode::Off {
            return Ok(());
        }
        let regions: Vec<Region> = {
            let authority = self.graph.formula_authority();
            authority
                .plane
                .name_dependent_span_refs(name)
                .into_iter()
                .filter_map(|span_ref| authority.plane.spans.get(span_ref))
                .map(|span| Region::from_domain(span.result_region.domain()))
                .collect()
        };
        for region in regions {
            self.demote_spans_preserving_computed_overlays(region.sheet_id(), region)
                .map_err(Self::editor_error_to_excel)?;
        }
        Ok(())
    }

    pub fn define_table(
        &mut self,
        name: &str,
        range: crate::reference::RangeRef,
        header_row: bool,
        headers: Vec<String>,
        totals_row: bool,
    ) -> Result<(), ExcelError> {
        self.graph
            .define_table(name, range, header_row, headers, totals_row)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        self.mark_topology_edited();
        Ok(())
    }

    pub fn define_source_scalar(
        &mut self,
        name: &str,
        version: Option<u64>,
    ) -> Result<(), ExcelError> {
        self.graph.define_source_scalar(name, version)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        self.mark_topology_edited();
        Ok(())
    }

    pub fn define_source_table(
        &mut self,
        name: &str,
        version: Option<u64>,
    ) -> Result<(), ExcelError> {
        self.graph.define_source_table(name, version)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        self.mark_topology_edited();
        Ok(())
    }

    pub fn set_source_scalar_version(
        &mut self,
        name: &str,
        version: Option<u64>,
    ) -> Result<(), ExcelError> {
        self.graph.set_source_scalar_version(name, version)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        Ok(())
    }

    pub fn set_source_table_version(
        &mut self,
        name: &str,
        version: Option<u64>,
    ) -> Result<(), ExcelError> {
        self.graph.set_source_table_version(name, version)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        Ok(())
    }

    pub fn invalidate_source(&mut self, name: &str) -> Result<(), ExcelError> {
        self.graph.invalidate_source(name)?;
        self.record_formula_plane_structural_change(StructuralScope::AllSheets);
        Ok(())
    }

    pub fn vertex_value(&self, vertex: VertexId) -> Option<LiteralValue> {
        self.graph.get_value(vertex)
    }

    pub fn graph_cell_value(&self, sheet: &str, row: u32, col: u32) -> Option<LiteralValue> {
        self.graph.get_cell_value(sheet, row, col)
    }

    pub fn vertex_for_cell(&self, cell: &CellRef) -> Option<VertexId> {
        self.graph.get_vertex_for_cell(cell)
    }

    pub fn evaluation_vertices(&self) -> Vec<VertexId> {
        self.graph.get_evaluation_vertices()
    }

    /// Return read-only baseline counters for FormulaPlane/dispatch benchmarking.
    pub fn baseline_stats(&self) -> EngineBaselineStats {
        let graph = self.graph.baseline_stats();
        let formula_authority = self.graph.formula_authority();
        EngineBaselineStats {
            graph_vertex_count: graph.graph_vertex_count,
            graph_formula_vertex_count: graph.graph_formula_vertex_count,
            graph_edge_count: graph.graph_edge_count,
            dirty_vertex_count: graph.dirty_vertex_count,
            evaluation_vertex_count: graph.evaluation_vertex_count,
            formula_ast_root_count: graph.formula_ast_root_count,
            formula_ast_node_count: graph.formula_ast_node_count,
            staged_formula_count: self.staged_formula_count(),
            formula_plane_active_span_count: formula_authority.active_span_count(),
            formula_plane_producer_result_entries: formula_authority.producer_results.len(),
            formula_plane_consumer_read_entries: formula_authority.consumer_reads.len(),
            formula_plane_cycle_member_span_demotions: self
                .formula_plane_cycle_member_span_demotions,
        }
    }

    #[cfg(test)]
    pub(crate) fn used_axis_bounds_cache_stats(&self) -> (usize, usize, usize, usize) {
        self.used_axis_bounds_cache
            .read()
            .ok()
            .and_then(|guard| {
                guard.as_ref().map(|cache| {
                    (
                        cache.row_hits.load(Ordering::Relaxed),
                        cache.row_misses.load(Ordering::Relaxed),
                        cache.col_hits.load(Ordering::Relaxed),
                        cache.col_misses.load(Ordering::Relaxed),
                    )
                })
            })
            .unwrap_or((0, 0, 0, 0))
    }

    pub fn set_first_load_assume_new(&mut self, enabled: bool) {
        self.graph.set_first_load_assume_new(enabled);
    }

    pub fn reset_ensure_touched(&mut self) {
        self.graph.reset_ensure_touched();
    }

    pub fn finalize_sheet_index(&mut self, sheet: &str) {
        self.graph.finalize_sheet_index(sheet);
    }

    /// Execute a named Engine action.
    ///
    /// Ticket 614 introduces this as the stable Engine-level transaction surface.
    /// For now actions are commit-only: they do not create changelog boundaries and they do not
    /// provide rollback/atomicity.
    ///
    /// Nested actions are deterministically handled by *disallowing* nesting: calling
    /// `Engine::action` while another action is active returns `EditorError::TransactionFailed`.
    pub fn action<T>(
        &mut self,
        name: impl AsRef<str>,
        f: impl FnOnce(&mut EngineAction<'_, R>) -> Result<T, crate::engine::EditorError>,
    ) -> Result<T, crate::engine::EditorError> {
        if self.action_depth != 0 {
            return Err(crate::engine::EditorError::TransactionFailed {
                reason: "Nested Engine::action calls are not supported (ticket 614: commit-only surface)"
                    .to_string(),
            });
        }

        self.action_depth = 1;
        let engine_ptr: *mut Engine<R> = self;
        let _guard = ActionDepthGuard {
            engine: engine_ptr,
            _marker: std::marker::PhantomData,
        };

        let mut tx = EngineAction {
            engine: self,
            name: name.as_ref().to_string(),
            log: None,
            arrow_undo: None,
            atomic_policy: false,
        };
        f(&mut tx)
    }

    /// Execute a named Engine action with atomic commit/rollback semantics.
    ///
    /// This variant does not require a `ChangeLog` and uses an internal journal for rollback.
    pub fn action_atomic<T>(
        &mut self,
        name: impl Into<String>,
        f: impl FnOnce(&mut EngineAction<'_, R>) -> Result<T, crate::engine::EditorError>,
    ) -> Result<T, crate::engine::EditorError> {
        let (v, _j) = self.action_atomic_journal(name, f)?;
        Ok(v)
    }

    /// Like `action_atomic`, but returns the committed journal entry for undo/redo storage.
    pub fn action_atomic_journal<T>(
        &mut self,
        name: impl Into<String>,
        f: impl FnOnce(&mut EngineAction<'_, R>) -> Result<T, crate::engine::EditorError>,
    ) -> Result<(T, crate::engine::ActionJournal), crate::engine::EditorError> {
        if self.action_depth != 0 {
            return Err(crate::engine::EditorError::TransactionFailed {
                reason: "Nested Engine::action calls are not supported (deterministic rule)"
                    .to_string(),
            });
        }

        self.action_depth = 1;
        let engine_ptr: *mut Engine<R> = self;
        let _guard = ActionDepthGuard {
            engine: engine_ptr,
            _marker: std::marker::PhantomData,
        };

        let name_str = name.into();
        let mut log = crate::engine::ChangeLog::new();
        let start_len = log.len();
        self.action_atomic_impl(&mut log, start_len, name_str, f)
    }

    fn action_atomic_impl<T>(
        &mut self,
        log: &mut crate::engine::ChangeLog,
        start_len: usize,
        name: String,
        f: impl FnOnce(&mut EngineAction<'_, R>) -> Result<T, crate::engine::EditorError>,
    ) -> Result<(T, crate::engine::ActionJournal), crate::engine::EditorError> {
        let mut arrow_undo = crate::engine::ArrowUndoBatch::default();
        let arrow_ptr: *mut crate::engine::ArrowUndoBatch = &mut arrow_undo;

        let log_ptr: *mut crate::engine::ChangeLog = log;
        let mut tx = EngineAction {
            engine: self,
            name: name.clone(),
            log: Some(log_ptr),
            arrow_undo: Some(arrow_ptr),
            atomic_policy: true,
        };

        let res = f(&mut tx);

        // Capture graph structural delta for this action.
        let graph_events: Vec<crate::engine::ChangeEvent> =
            unsafe { (&*log_ptr).events() }[start_len..].to_vec();
        let graph_batch = crate::engine::GraphUndoBatch {
            events: graph_events,
        };
        let affected_cells = arrow_undo.ops.len();
        let journal = crate::engine::ActionJournal {
            name,
            graph: graph_batch,
            arrow: arrow_undo,
            affected_cells,
        };

        match res {
            Ok(v) => {
                if !journal.graph.is_empty() || !journal.arrow.is_empty() {
                    for event in &journal.graph.events {
                        self.record_formula_plane_change_for_event(event);
                    }
                    self.mark_data_edited();
                }
                Ok((v, journal))
            }
            Err(e) => {
                if let Err(rb) = self.rollback_from_action_journal(&journal) {
                    return Err(crate::engine::EditorError::TransactionFailed {
                        reason: format!(
                            "Engine::action_atomic rollback failed after error '{e}': {rb}"
                        ),
                    });
                }
                if !journal.graph.is_empty() || !journal.arrow.is_empty() {
                    for event in &journal.graph.events {
                        self.record_formula_plane_change_for_event(event);
                    }
                }
                Err(e)
            }
        }
    }

    /// Execute a named Engine action, logging graph changes into the provided ChangeLog.
    ///
    /// Ticket 615: this variant provides atomicity. If the action returns an error, it rolls back:
    /// - Dependency graph structural edits (via inverse ChangeEvents)
    /// - Arrow-truth overlay writes mirrored from ChangeEvents
    /// - ChangeLog entries (truncated back to the pre-action length)
    pub fn action_with_logger<T>(
        &mut self,
        log: &mut crate::engine::ChangeLog,
        name: impl AsRef<str>,
        f: impl FnOnce(&mut EngineAction<'_, R>) -> Result<T, crate::engine::EditorError>,
    ) -> Result<T, crate::engine::EditorError> {
        if self.action_depth != 0 {
            return Err(crate::engine::EditorError::TransactionFailed {
                reason: "Nested Engine::action calls are not supported (deterministic rule)"
                    .to_string(),
            });
        }

        self.action_depth = 1;
        let engine_ptr: *mut Engine<R> = self;
        let _guard = ActionDepthGuard {
            engine: engine_ptr,
            _marker: std::marker::PhantomData,
        };

        let start_len = log.len();
        let name_str = name.as_ref().to_string();
        log.begin_compound(name_str.clone());

        // Use the provided ChangeLog as an observability sink.
        // Correctness is provided by the internal `ActionJournal` returned from the atomic impl.
        let res = self.action_atomic_impl(log, start_len, name_str, f);

        match res {
            Ok((v, _journal)) => {
                log.end_compound();
                Ok(v)
            }
            Err(e) => {
                // Close compound and truncate log as cleanup only.
                log.end_compound();
                log.truncate(start_len);
                Err(e)
            }
        }
    }

    fn rollback_from_action_journal(
        &mut self,
        journal: &crate::engine::ActionJournal,
    ) -> Result<(), crate::engine::EditorError> {
        // 1) Roll back the dependency graph structure.
        journal.graph.undo(&mut self.graph)?;
        // 2) Roll back engine row-visibility sidecar events.
        self.apply_inverse_row_visibility_events(&journal.graph.events);
        // 3) Roll back Arrow-truth overlays.
        self.apply_arrow_undo_batch(&journal.arrow, /*undo=*/ true);
        Ok(())
    }

    fn rollback_from_change_events(
        &mut self,
        events: &[crate::engine::ChangeEvent],
    ) -> Result<(), crate::engine::EditorError> {
        use crate::engine::ChangeEvent;

        // 1) Roll back the dependency graph.
        {
            let mut editor = crate::engine::VertexEditor::new(&mut self.graph);
            let mut compound_stack: Vec<usize> = Vec::new();
            for ev in events.iter().rev() {
                match ev {
                    ChangeEvent::CompoundEnd { depth } => compound_stack.push(*depth),
                    ChangeEvent::CompoundStart { depth, .. } => {
                        if compound_stack.last() == Some(depth) {
                            compound_stack.pop();
                        }
                    }
                    ChangeEvent::SetRowVisibility { .. } => {
                        // Engine-side metadata handled after dropping graph editor borrow.
                    }
                    _ => {
                        editor.apply_inverse(ev.clone())?;
                    }
                }
            }
        }

        // 2) Roll back engine row-visibility metadata.
        for ev in events.iter().rev() {
            self.apply_inverse_row_visibility_event(ev);
        }

        // 3) Roll back Arrow-truth overlays mirrored from those ChangeEvents.
        for ev in events.iter().rev() {
            self.mirror_inverse_change_to_arrow(ev);
        }

        Ok(())
    }

    fn read_cell_formula_ast(&self, sheet: &str, row: u32, col: u32) -> Option<ASTNode> {
        let sheet_id = self.graph.sheet_id(sheet)?;
        let coord = Coord::from_excel(row, col, true, true);
        let cell = CellRef::new(sheet_id, coord);
        let vid = self.graph.get_vertex_for_cell(&cell)?;
        let ast_id = self.graph.get_formula_id(vid)?;
        self.graph
            .data_store()
            .retrieve_ast(ast_id, self.graph.sheet_reg())
    }

    pub fn edit_with_logger<T>(
        &mut self,
        log: &mut crate::engine::ChangeLog,
        f: impl FnOnce(&mut crate::engine::VertexEditor) -> T,
    ) -> T {
        // Record starting log length so we can mirror only newly-recorded events.
        let start_len = log.len();

        // Provide a spill snapshot reader so VertexEditor can snapshot Arrow-truth spill values
        // (graph value cache is intentionally empty in canonical mode).
        struct ArrowSpillReader<'a> {
            sheets: &'a crate::arrow_store::SheetStore,
        }
        impl crate::engine::graph::editor::vertex_editor::SpillValueReader for ArrowSpillReader<'_> {
            fn read_cell_value(
                &self,
                sheet: &str,
                row: u32,
                col: u32,
            ) -> Option<formualizer_common::LiteralValue> {
                use formualizer_common::LiteralValue;
                let asheet = self.sheets.sheet(sheet)?;
                let r0 = row.saturating_sub(1) as usize;
                let c0 = col.saturating_sub(1) as usize;
                let v = asheet.get_cell_value(r0, c0);
                if matches!(v, LiteralValue::Empty) {
                    None
                } else {
                    Some(v)
                }
            }
        }

        let ret = {
            let spill_reader = ArrowSpillReader {
                sheets: &self.arrow_sheets,
            };
            let mut editor = crate::engine::VertexEditor::with_logger_and_spill_reader(
                &mut self.graph,
                log,
                &spill_reader,
            );
            f(&mut editor)
        };

        // Mirror value-impacting graph events to Arrow for forward edits.
        // This keeps Arrow overlays (delta + computed) consistent when edits clear/commit spills.
        for ev in &log.events()[start_len..] {
            self.mirror_forward_change_to_arrow(ev);
        }
        for ev in &log.events()[start_len..] {
            self.record_formula_plane_change_for_event(ev);
        }

        ret
    }

    pub fn undo_logged(
        &mut self,
        undo: &mut crate::engine::graph::editor::undo_engine::UndoEngine,
        log: &mut crate::engine::ChangeLog,
    ) -> Result<(), crate::engine::EditorError> {
        let batch = undo.undo(&mut self.graph, log)?;
        for item in batch.iter().rev() {
            self.apply_inverse_row_visibility_event(&item.event);
            self.apply_inverse_staged_formula_event(&item.event);
        }
        self.mirror_undo_batch_to_arrow(&batch);
        if !batch.is_empty() {
            for item in &batch {
                self.record_formula_plane_change_for_event(&item.event);
            }
        }
        Ok(())
    }

    pub fn redo_logged(
        &mut self,
        undo: &mut crate::engine::graph::editor::undo_engine::UndoEngine,
        log: &mut crate::engine::ChangeLog,
    ) -> Result<(), crate::engine::EditorError> {
        let batch = undo.redo(&mut self.graph, log)?;
        for item in &batch {
            self.apply_forward_row_visibility_event(&item.event);
            self.apply_forward_staged_formula_event(&item.event);
        }
        self.mirror_redo_batch_to_arrow(&batch);
        if !batch.is_empty() {
            for item in &batch {
                self.record_formula_plane_change_for_event(&item.event);
            }
        }
        Ok(())
    }

    /// Undo the last committed atomic action using the journal stack.
    ///
    /// This path does not require a `ChangeLog`.
    pub fn undo_action(
        &mut self,
        undo: &mut crate::engine::graph::editor::undo_engine::UndoEngine,
    ) -> Result<(), crate::engine::EditorError> {
        let Some(journal) = undo.pop_undo_action() else {
            return Ok(());
        };

        journal.graph.undo(&mut self.graph)?;
        self.apply_inverse_row_visibility_events(&journal.graph.events);
        self.apply_arrow_undo_batch(&journal.arrow, /*undo=*/ true);
        if !journal.graph.is_empty() || !journal.arrow.is_empty() {
            for event in &journal.graph.events {
                self.record_formula_plane_change_for_event(event);
            }
            self.mark_data_edited();
        }

        undo.push_redo_action(journal);
        Ok(())
    }

    /// Redo the last undone atomic action using the journal stack.
    ///
    /// This path does not require a `ChangeLog`.
    pub fn redo_action(
        &mut self,
        undo: &mut crate::engine::graph::editor::undo_engine::UndoEngine,
    ) -> Result<(), crate::engine::EditorError> {
        let Some(journal) = undo.pop_redo_action() else {
            return Ok(());
        };

        journal.graph.redo(&mut self.graph)?;
        self.apply_forward_row_visibility_events(&journal.graph.events);
        self.apply_arrow_undo_batch(&journal.arrow, /*undo=*/ false);
        if !journal.graph.is_empty() || !journal.arrow.is_empty() {
            for event in &journal.graph.events {
                self.record_formula_plane_change_for_event(event);
            }
            self.mark_data_edited();
        }

        undo.push_done_action(journal);
        Ok(())
    }

    fn cellref_to_sheet_row_col(&self, addr: &crate::reference::CellRef) -> (String, u32, u32) {
        let sheet = self.graph.sheet_name(addr.sheet_id).to_string();
        // Coord stores 0-based indices.
        let row = addr.coord.row() + 1;
        let col = addr.coord.col() + 1;
        (sheet, row, col)
    }

    fn mirror_undo_batch_to_arrow(
        &mut self,
        batch: &[crate::engine::graph::editor::undo_engine::UndoBatchItem],
    ) {
        // Undo applies inverses in reverse order.
        for item in batch.iter().rev() {
            self.mirror_inverse_change_to_arrow(&item.event);
        }
    }

    fn mirror_redo_batch_to_arrow(
        &mut self,
        batch: &[crate::engine::graph::editor::undo_engine::UndoBatchItem],
    ) {
        // Redo applies events in forward order.
        for item in batch.iter() {
            self.mirror_forward_change_to_arrow(&item.event);
        }
    }

    fn mirror_inverse_change_to_arrow(&mut self, ev: &crate::engine::ChangeEvent) {
        use crate::engine::ChangeEvent;
        use formualizer_common::LiteralValue;

        match ev {
            ChangeEvent::SetValue {
                addr,
                old_value,
                old_formula,
                ..
            } => {
                let (sheet, row, col) = self.cellref_to_sheet_row_col(addr);
                if old_formula.is_some() {
                    self.clear_delta_overlay_cell(&sheet, row, col);
                } else {
                    let v = old_value.clone().unwrap_or(LiteralValue::Empty);
                    self.mirror_value_to_overlay(&sheet, row, col, &v);
                }
            }
            ChangeEvent::SetFormula {
                addr,
                old_value,
                old_formula,
                ..
            } => {
                let (sheet, row, col) = self.cellref_to_sheet_row_col(addr);
                if old_formula.is_some() {
                    self.clear_delta_overlay_cell(&sheet, row, col);
                } else {
                    let v = old_value.clone().unwrap_or(LiteralValue::Empty);
                    self.mirror_value_to_overlay(&sheet, row, col, &v);
                }
            }
            ChangeEvent::SpillCommitted { old, new, .. } => {
                // Inverse: restore `old` (or clear if none).
                self.mirror_spill_snapshot(new, /*clear_only=*/ true);
                if let Some(snap) = old {
                    self.mirror_spill_snapshot(snap, /*clear_only=*/ false);
                }
            }
            ChangeEvent::SpillCleared { old, .. } => {
                // Inverse: restore prior spill.
                self.mirror_spill_snapshot(old, /*clear_only=*/ false);
            }
            ChangeEvent::SetRowVisibility { .. } => {
                // Engine-side metadata only; no Arrow overlay effect.
            }
            _ => {}
        }
    }

    fn mirror_forward_change_to_arrow(&mut self, ev: &crate::engine::ChangeEvent) {
        use crate::engine::ChangeEvent;

        match ev {
            ChangeEvent::SetValue { addr, new, .. } => {
                let (sheet, row, col) = self.cellref_to_sheet_row_col(addr);
                self.mirror_value_to_overlay(&sheet, row, col, new);
            }
            ChangeEvent::SetFormula { addr, .. } => {
                let (sheet, row, col) = self.cellref_to_sheet_row_col(addr);
                self.clear_delta_overlay_cell(&sheet, row, col);
                // Keep any computed overlay for this cell as-is; it will be recomputed on demand.
            }
            ChangeEvent::SpillCommitted { old, new, .. } => {
                if let Some(snap) = old {
                    self.mirror_spill_snapshot(snap, /*clear_only=*/ true);
                }
                self.mirror_spill_snapshot(new, /*clear_only=*/ false);
            }
            ChangeEvent::SpillCleared { old, .. } => {
                self.mirror_spill_snapshot(old, /*clear_only=*/ true);
            }
            ChangeEvent::SetRowVisibility { .. } => {
                // Engine-side metadata only; no Arrow overlay effect.
            }
            _ => {
                // Other graph structural operations do not have direct value effects in Arrow.
            }
        }
    }

    fn mirror_spill_snapshot(
        &mut self,
        snap: &crate::engine::graph::editor::change_log::SpillSnapshot,
        clear_only: bool,
    ) {
        use formualizer_common::LiteralValue;

        let mut i = 0usize;
        for row in &snap.values {
            for v in row {
                if let Some(cell) = snap.target_cells.get(i) {
                    let (sheet, r, c) = self.cellref_to_sheet_row_col(cell);
                    let out = if clear_only {
                        LiteralValue::Empty
                    } else {
                        v.clone()
                    };
                    self.mirror_value_to_computed_overlay(&sheet, r, c, &out);
                }
                i += 1;
            }
        }
        // If target_cells is longer than values (should not happen), clear remaining cells.
        if clear_only {
            for cell in snap.target_cells.iter().skip(i) {
                let (sheet, r, c) = self.cellref_to_sheet_row_col(cell);
                self.mirror_value_to_computed_overlay(&sheet, r, c, &LiteralValue::Empty);
            }
        }
    }

    pub fn set_default_sheet_by_name(&mut self, name: &str) {
        self.graph.set_default_sheet_by_name(name);
    }

    pub fn set_default_sheet_by_id(&mut self, id: SheetId) {
        self.graph.set_default_sheet_by_id(id);
    }

    pub fn set_sheet_index_mode(&mut self, mode: crate::engine::SheetIndexMode) {
        self.graph.set_sheet_index_mode(mode);
    }

    fn clear_cached_static_schedule(&mut self) {
        self.cached_static_schedule = None;
    }

    /// Mark data edited: bump snapshot and set edited flag.
    /// Value-only edits keep the stable-topology schedule cache alive.
    pub fn mark_data_edited(&mut self) {
        self.snapshot_id
            .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
        self.has_edited = true;
    }

    /// Mark a topology-changing edit: bump snapshot + topology epoch and invalidate cached schedules.
    pub fn mark_topology_edited(&mut self) {
        self.snapshot_id
            .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
        self.topology_epoch = self.topology_epoch.wrapping_add(1);
        self.clear_cached_static_schedule();
        self.has_edited = true;
    }

    fn mark_all_formula_vertices_dirty(&mut self) {
        let vertices: Vec<VertexId> = self.graph.vertices_with_formulas().collect();
        for vertex in vertices {
            self.graph.mark_vertex_dirty(vertex);
        }
    }

    fn mark_moved_formula_vertices_dirty(
        &mut self,
        summary: &crate::engine::graph::editor::vertex_editor::ShiftSummary,
    ) {
        for vertex in &summary.vertices_moved {
            if self.graph.get_formula_id(*vertex).is_some() {
                self.graph.mark_vertex_dirty(*vertex);
            }
        }
    }

    /// Access Arrow sheet store (read-only)
    pub fn sheet_store(&self) -> &SheetStore {
        &self.arrow_sheets
    }

    /// Access Arrow sheet store (mutable)
    pub fn sheet_store_mut(&mut self) -> &mut SheetStore {
        &mut self.arrow_sheets
    }

    pub fn has_staged_formulas(&self) -> bool {
        !self.staged_formulas.is_empty()
    }

    pub fn staged_formula_count(&self) -> usize {
        self.staged_formulas.values().map(StagedSheet::len).sum()
    }

    /// Stage a formula text instead of inserting into the graph (used when deferring is enabled).
    pub fn stage_formula_text(&mut self, sheet: &str, row: u32, col: u32, text: String) {
        self.staged_formulas
            .entry(sheet.to_string())
            .or_default()
            .stage(row, col, text);
    }

    pub fn clear_staged_formula_text(&mut self, sheet: &str, row: u32, col: u32) -> Option<String> {
        let mut removed = None;
        let mut remove_sheet = false;
        if let Some(entries) = self.staged_formulas.get_mut(sheet) {
            removed = entries.remove(row, col);
            remove_sheet = entries.is_empty();
        }
        if remove_sheet {
            self.staged_formulas.remove(sheet);
        }
        removed
    }

    pub fn clear_staged_formulas_for_sheet(&mut self, sheet: &str) {
        self.staged_formulas.remove(sheet);
    }

    pub fn rename_staged_formula_sheet(&mut self, old: &str, new: &str) {
        let Some(entries) = self.staged_formulas.remove(old) else {
            return;
        };
        for (row, col, text) in entries.into_entries() {
            self.stage_formula_text(new, row, col, text);
        }
    }

    /// Get a staged formula text for a given cell if present (cloned).
    pub fn get_staged_formula_text(&self, sheet: &str, row: u32, col: u32) -> Option<String> {
        self.staged_formulas
            .get(sheet)
            .and_then(|v| v.get(row, col).map(str::to_owned))
    }

    pub fn formula_parse_diagnostics(&self) -> &[FormulaParseDiagnostic] {
        &self.formula_parse_diagnostics
    }

    pub fn take_formula_parse_diagnostics(&mut self) -> Vec<FormulaParseDiagnostic> {
        std::mem::take(&mut self.formula_parse_diagnostics)
    }

    pub fn clear_formula_parse_diagnostics(&mut self) {
        self.formula_parse_diagnostics.clear();
    }

    pub fn last_formula_ingest_report(&self) -> Option<&FormulaIngestReport> {
        self.last_formula_ingest_report.as_ref()
    }

    pub fn formula_ingest_report_total(&self) -> &FormulaIngestReport {
        &self.formula_ingest_report_total
    }

    #[cfg(test)]
    pub(crate) fn last_formula_plane_span_eval_report(&self) -> Option<&SpanEvalReport> {
        self.last_formula_plane_span_eval_report.as_ref()
    }

    #[cfg(test)]
    pub(crate) fn formula_plane_indexes_epoch(&self) -> u64 {
        self.graph.formula_authority().indexes_epoch()
    }

    #[cfg(test)]
    pub(crate) fn formula_plane_capacity_bailouts(&self) -> u64 {
        self.formula_plane_capacity_bailouts
    }

    fn record_formula_ingest_report(&mut self, report: FormulaIngestReport) {
        self.formula_ingest_report_total.mode = report.mode;
        self.formula_ingest_report_total.accumulate(&report);
        self.last_formula_ingest_report = Some(report);
    }

    fn analyze_formula_plane_shadow_candidates(
        &mut self,
        batches: &[FormulaIngestBatch],
    ) -> FormulaIngestReport {
        let mut report = FormulaIngestReport::with_mode(FormulaPlaneMode::Shadow);
        report.formula_cells_seen = batches.iter().map(|batch| batch.len() as u64).sum();

        // Touch graph-owned authority deliberately: Tranche 3 shadow analysis uses
        // scratch state, but FormulaPlane ownership now lives on DependencyGraph.
        let _active_epoch = self.graph.formula_authority().plane.epoch();

        let batch_sheet_ids: Vec<SheetId> = batches
            .iter()
            .map(|batch| self.graph.sheet_id_mut(&batch.sheet_name))
            .collect();
        let mut groups: BTreeMap<
            (SheetId, u64, u32),
            Vec<(FormulaPlacementCandidate, CandidateAnalysis)>,
        > = BTreeMap::new();
        {
            let mut pipeline = self.ingest_pipeline();
            for (batch, sheet_id) in batches.iter().zip(batch_sheet_ids.iter().copied()) {
                for record in &batch.formulas {
                    if record.row == 0 || record.col == 0 {
                        report.shadow_candidate_cells =
                            report.shadow_candidate_cells.saturating_add(1);
                        report.shadow_fallback_cells =
                            report.shadow_fallback_cells.saturating_add(1);
                        Self::record_shadow_fallback_reason(
                            &mut report,
                            PlacementFallbackReason::UnsupportedShapeOrGaps,
                            1,
                        );
                        continue;
                    }

                    let placement = CellRef::new(
                        sheet_id,
                        Coord::from_excel(record.row, record.col, true, true),
                    );
                    let ingested = match pipeline.ingest_formula(
                        FormulaAstInput::RawArena(record.ast_id),
                        placement,
                        record.formula_text.clone(),
                    ) {
                        Ok(ingested) => ingested,
                        Err(_) => {
                            report.shadow_candidate_cells =
                                report.shadow_candidate_cells.saturating_add(1);
                            report.shadow_fallback_cells =
                                report.shadow_fallback_cells.saturating_add(1);
                            Self::record_shadow_fallback_reason(
                                &mut report,
                                PlacementFallbackReason::UnsupportedCanonicalTemplate,
                                1,
                            );
                            continue;
                        }
                    };
                    let candidate = FormulaPlacementCandidate::new(
                        sheet_id,
                        record.row - 1,
                        record.col - 1,
                        ingested.ast_id,
                        record.formula_text.clone(),
                    );
                    let analysis = match CandidateAnalysis::from_ingested(&candidate, &ingested) {
                        Ok(analysis) => analysis,
                        Err(reason) => {
                            report.shadow_candidate_cells =
                                report.shadow_candidate_cells.saturating_add(1);
                            report.shadow_fallback_cells =
                                report.shadow_fallback_cells.saturating_add(1);
                            Self::record_shadow_fallback_reason(&mut report, reason, 1);
                            continue;
                        }
                    };
                    groups
                        .entry((
                            sheet_id,
                            ingested.parameterized_canonical_hash,
                            candidate.col,
                        ))
                        .or_default()
                        .push((candidate, analysis));
                }
            }
        }

        let mut scratch_plane = FormulaPlane::default();
        for entries in groups.into_values() {
            let (candidates, analyses): (Vec<_>, Vec<_>) = entries.into_iter().unzip();
            for (component, component_analyses) in
                Self::split_candidate_components_with_analyses(candidates, analyses)
            {
                let placement_report = place_candidate_family_with_analyses(
                    &mut scratch_plane,
                    component,
                    component_analyses,
                );
                let counters = placement_report.counters;
                report.shadow_candidate_cells = report
                    .shadow_candidate_cells
                    .saturating_add(counters.formula_cells_seen);
                report.shadow_accepted_span_cells = report
                    .shadow_accepted_span_cells
                    .saturating_add(counters.accepted_span_cells);
                report.shadow_fallback_cells = report
                    .shadow_fallback_cells
                    .saturating_add(counters.legacy_cells);
                report.shadow_templates_interned = report
                    .shadow_templates_interned
                    .saturating_add(counters.templates_interned);
                report.shadow_spans_created = report
                    .shadow_spans_created
                    .saturating_add(counters.spans_created);
                report.graph_formula_vertices_avoided_shadow = report
                    .graph_formula_vertices_avoided_shadow
                    .saturating_add(counters.formula_vertices_avoided);
                report.ast_roots_avoided_shadow = report
                    .ast_roots_avoided_shadow
                    .saturating_add(counters.ast_roots_avoided);
                report.edge_rows_avoided_shadow = report
                    .edge_rows_avoided_shadow
                    .saturating_add(counters.edge_rows_avoided);
                for (reason, count) in counters.fallback_reasons {
                    Self::record_shadow_fallback_reason(&mut report, reason, count);
                }
            }
        }
        report
    }

    fn record_shadow_fallback_reason(
        report: &mut FormulaIngestReport,
        reason: PlacementFallbackReason,
        count: u64,
    ) {
        *report
            .fallback_reasons
            .entry(format!("{reason:?}"))
            .or_default() += count;
    }

    fn analyze_formula_plane_authoritative_ingest(
        &mut self,
        batches: &[FormulaIngestBatch],
    ) -> (
        FormulaIngestReport,
        Vec<FormulaIngestBatch>,
        PlannedFormulaMaterialize,
    ) {
        let mut report =
            FormulaIngestReport::with_mode(FormulaPlaneMode::AuthoritativeExperimental);
        report.formula_cells_seen = batches.iter().map(|batch| batch.len() as u64).sum();

        let mut pending_candidates: Vec<(String, FormulaPlacementCandidate)> = Vec::new();
        let mut fallback: BTreeMap<String, Vec<FormulaIngestRecord>> = BTreeMap::new();
        let mut planned_fallback: PlannedFormulaMaterialize = BTreeMap::new();

        for batch in batches {
            let sheet_id = self.graph.sheet_id_mut(&batch.sheet_name);
            for record in &batch.formulas {
                if record.row == 0 || record.col == 0 {
                    report.shadow_candidate_cells = report.shadow_candidate_cells.saturating_add(1);
                    report.shadow_fallback_cells = report.shadow_fallback_cells.saturating_add(1);
                    Self::record_shadow_fallback_reason(
                        &mut report,
                        PlacementFallbackReason::UnsupportedShapeOrGaps,
                        1,
                    );
                    fallback
                        .entry(batch.sheet_name.clone())
                        .or_default()
                        .push(record.clone());
                    continue;
                }

                pending_candidates.push((
                    batch.sheet_name.clone(),
                    FormulaPlacementCandidate::new(
                        sheet_id,
                        record.row - 1,
                        record.col - 1,
                        record.ast_id,
                        record.formula_text.clone(),
                    ),
                ));
            }
        }

        let mut groups: BTreeMap<(SheetId, u64, u32), Vec<usize>> = BTreeMap::new();
        let mut analyses_by_index: Vec<Option<CandidateAnalysis>> =
            (0..pending_candidates.len()).map(|_| None).collect();
        let mut plans_by_index: Vec<Option<DependencyPlanRow>> =
            (0..pending_candidates.len()).map(|_| None).collect();
        {
            let mut pipeline = self.ingest_pipeline();
            for (idx, (sheet_name, candidate)) in pending_candidates.iter_mut().enumerate() {
                let placement = CellRef::new(
                    candidate.sheet_id,
                    Coord::from_excel(
                        candidate.row.saturating_add(1),
                        candidate.col.saturating_add(1),
                        true,
                        true,
                    ),
                );
                let ingested = pipeline.ingest_formula(
                    FormulaAstInput::RawArena(candidate.ast_id),
                    placement,
                    candidate.formula_text.clone(),
                );
                match ingested {
                    Ok(ingested) => {
                        candidate.ast_id = ingested.ast_id;
                        let canonical_hash = ingested.parameterized_canonical_hash;
                        let dep_plan = ingested.dep_plan.clone();
                        match CandidateAnalysis::from_ingested(candidate, &ingested) {
                            Ok(analysis) => {
                                groups
                                    .entry((candidate.sheet_id, canonical_hash, candidate.col))
                                    .or_default()
                                    .push(idx);
                                analyses_by_index[idx] = Some(analysis);
                                plans_by_index[idx] = Some(dep_plan);
                            }
                            Err(reason) => {
                                report.shadow_candidate_cells =
                                    report.shadow_candidate_cells.saturating_add(1);
                                report.shadow_fallback_cells =
                                    report.shadow_fallback_cells.saturating_add(1);
                                Self::record_shadow_fallback_reason(&mut report, reason, 1);
                                planned_fallback
                                    .entry(sheet_name.clone())
                                    .or_default()
                                    .push((
                                        candidate.row.saturating_add(1),
                                        candidate.col.saturating_add(1),
                                        candidate.ast_id,
                                        dep_plan,
                                    ));
                            }
                        }
                    }
                    Err(_) => {
                        report.shadow_candidate_cells =
                            report.shadow_candidate_cells.saturating_add(1);
                        report.shadow_fallback_cells =
                            report.shadow_fallback_cells.saturating_add(1);
                        Self::record_shadow_fallback_reason(
                            &mut report,
                            PlacementFallbackReason::UnsupportedCanonicalTemplate,
                            1,
                        );
                        fallback.entry(sheet_name.clone()).or_default().push(
                            FormulaIngestRecord::new(
                                candidate.row.saturating_add(1),
                                candidate.col.saturating_add(1),
                                candidate.ast_id,
                                candidate.formula_text.clone(),
                            ),
                        );
                    }
                }
            }
        }

        for ((_sheet_id, _canonical_hash, _col), candidate_indices) in groups {
            let sheet_name = pending_candidates[candidate_indices[0]].0.clone();
            let mut plans_by_coord: BTreeMap<(u32, u32), Vec<DependencyPlanRow>> = BTreeMap::new();
            for idx in &candidate_indices {
                // Each candidate index belongs to exactly one group, so the
                // plan row can be moved out instead of deep-cloned.
                if let Some(plan) = plans_by_index[*idx].take() {
                    let candidate = &pending_candidates[*idx].1;
                    plans_by_coord
                        .entry((candidate.row, candidate.col))
                        .or_default()
                        .push(plan);
                }
            }
            let candidates: Vec<_> = candidate_indices
                .iter()
                .map(|idx| pending_candidates[*idx].1.clone())
                .collect();
            let components = Self::split_shadow_candidate_components(candidates);
            let analyzed_components =
                if components.len() == 1 && components[0].len() == candidate_indices.len() {
                    let component = components.into_iter().next().expect("one component");
                    let component_analyses = candidate_indices
                        .iter()
                        .map(|idx| {
                            analyses_by_index[*idx]
                                .take()
                                .expect("candidate analysis must be used once")
                        })
                        .collect();
                    vec![(component, component_analyses)]
                } else {
                    let mut indices_by_coord: BTreeMap<(u32, u32), Vec<usize>> = BTreeMap::new();
                    for idx in candidate_indices.iter().rev() {
                        let candidate = &pending_candidates[*idx].1;
                        indices_by_coord
                            .entry((candidate.row, candidate.col))
                            .or_default()
                            .push(*idx);
                    }

                    components
                        .into_iter()
                        .map(|component| {
                            let mut component_analyses = Vec::with_capacity(component.len());
                            for candidate in &component {
                                let idx = indices_by_coord
                                    .get_mut(&(candidate.row, candidate.col))
                                    .and_then(Vec::pop)
                                    .expect("component candidate must have a precomputed analysis");
                                component_analyses.push(
                                    analyses_by_index[idx]
                                        .take()
                                        .expect("candidate analysis must be used once"),
                                );
                            }
                            (component, component_analyses)
                        })
                        .collect()
                };

            for (component, component_analyses) in analyzed_components {
                for (component, component_analyses) in
                    split_candidate_affine_literal_runs(component, component_analyses)
                {
                    let placement_report = {
                        let authority = self.graph.formula_authority_mut();
                        place_candidate_family_with_analyses(
                            &mut authority.plane,
                            component.clone(),
                            component_analyses,
                        )
                    };
                    Self::accumulate_formula_plane_placement_report(&mut report, &placement_report);

                    // Index candidates by placement once per component. The
                    // previous per-result linear `find` made this fallback
                    // mapping O(N²) for rejected families (e.g. an N-cell
                    // chain rejected with `InternalDependency`), dominating
                    // first-eval ingest cost on large rejected families.
                    // First insert wins, matching the old `Iterator::find`
                    // semantics for duplicate placements.
                    let mut candidate_by_placement: FxHashMap<
                        crate::formula_plane::runtime::PlacementCoord,
                        &FormulaPlacementCandidate,
                    > = FxHashMap::with_capacity_and_hasher(component.len(), Default::default());
                    for candidate in &component {
                        candidate_by_placement
                            .entry(candidate.placement())
                            .or_insert(candidate);
                    }
                    for result in &placement_report.results {
                        let FormulaPlacementResult::Legacy { placement, .. } = result else {
                            continue;
                        };
                        if let Some(&candidate) = candidate_by_placement.get(placement) {
                            let plan = plans_by_coord
                                .get_mut(&(candidate.row, candidate.col))
                                .and_then(Vec::pop);
                            if let Some(plan) = plan {
                                planned_fallback
                                    .entry(sheet_name.clone())
                                    .or_default()
                                    .push((
                                        candidate.row.saturating_add(1),
                                        candidate.col.saturating_add(1),
                                        candidate.ast_id,
                                        plan,
                                    ));
                            } else {
                                fallback.entry(sheet_name.clone()).or_default().push(
                                    FormulaIngestRecord::new(
                                        candidate.row.saturating_add(1),
                                        candidate.col.saturating_add(1),
                                        candidate.ast_id,
                                        candidate.formula_text.clone(),
                                    ),
                                );
                            }
                        }
                    }
                }
            }
        }

        let _index_report = self.graph.formula_authority_mut().rebuild_indexes();

        let fallback_batches = fallback
            .into_iter()
            .map(|(sheet_name, formulas)| FormulaIngestBatch::new(sheet_name, formulas))
            .collect();
        (report, fallback_batches, planned_fallback)
    }

    fn accumulate_formula_plane_placement_report(
        report: &mut FormulaIngestReport,
        placement_report: &crate::formula_plane::placement::FormulaPlacementReport,
    ) {
        let counters = &placement_report.counters;
        report.shadow_candidate_cells = report
            .shadow_candidate_cells
            .saturating_add(counters.formula_cells_seen);
        report.shadow_accepted_span_cells = report
            .shadow_accepted_span_cells
            .saturating_add(counters.accepted_span_cells);
        report.shadow_fallback_cells = report
            .shadow_fallback_cells
            .saturating_add(counters.legacy_cells);
        report.shadow_templates_interned = report
            .shadow_templates_interned
            .saturating_add(counters.templates_interned);
        report.shadow_spans_created = report
            .shadow_spans_created
            .saturating_add(counters.spans_created);
        report.graph_formula_vertices_avoided_shadow = report
            .graph_formula_vertices_avoided_shadow
            .saturating_add(counters.formula_vertices_avoided);
        report.ast_roots_avoided_shadow = report
            .ast_roots_avoided_shadow
            .saturating_add(counters.ast_roots_avoided);
        report.edge_rows_avoided_shadow = report
            .edge_rows_avoided_shadow
            .saturating_add(counters.edge_rows_avoided);
        for (reason, count) in &counters.fallback_reasons {
            Self::record_shadow_fallback_reason(report, *reason, *count);
        }
    }

    fn split_candidate_components_with_analyses(
        candidates: Vec<FormulaPlacementCandidate>,
        mut analyses: Vec<CandidateAnalysis>,
    ) -> Vec<(Vec<FormulaPlacementCandidate>, Vec<CandidateAnalysis>)> {
        let components = Self::split_shadow_candidate_components(candidates.clone());
        let mut analysis_by_coord: BTreeMap<(u32, u32), Vec<CandidateAnalysis>> = BTreeMap::new();
        for (candidate, analysis) in candidates.into_iter().zip(analyses.drain(..)) {
            analysis_by_coord
                .entry((candidate.row, candidate.col))
                .or_default()
                .push(analysis);
        }
        components
            .into_iter()
            .flat_map(|component| {
                let mut component_analyses = Vec::with_capacity(component.len());
                for candidate in &component {
                    let analysis = analysis_by_coord
                        .get_mut(&(candidate.row, candidate.col))
                        .and_then(Vec::pop)
                        .expect("component candidate must have a precomputed analysis");
                    component_analyses.push(analysis);
                }
                split_candidate_affine_literal_runs(component, component_analyses)
            })
            .collect()
    }

    fn split_shadow_candidate_components(
        candidates: Vec<FormulaPlacementCandidate>,
    ) -> Vec<Vec<FormulaPlacementCandidate>> {
        if candidates.len() <= 1 {
            return vec![candidates];
        }

        // Fast path: candidates already ordered as one contiguous
        // single-column (or single-row) run form exactly one 4-connected
        // component in their existing (row, col) order; skip the BFS.
        let is_row_run = candidates.windows(2).all(|w| {
            w[0].sheet_id == w[1].sheet_id && w[0].col == w[1].col && w[0].row + 1 == w[1].row
        });
        let is_col_run = candidates.windows(2).all(|w| {
            w[0].sheet_id == w[1].sheet_id && w[0].row == w[1].row && w[0].col + 1 == w[1].col
        });
        if is_row_run || is_col_run {
            return vec![candidates];
        }

        let mut coord_to_indices: BTreeMap<(u32, u32), Vec<usize>> = BTreeMap::new();
        for (idx, candidate) in candidates.iter().enumerate() {
            coord_to_indices
                .entry((candidate.row, candidate.col))
                .or_default()
                .push(idx);
        }

        let mut remaining: BTreeSet<usize> = (0..candidates.len()).collect();
        let mut components = Vec::new();
        while let Some(&start) = remaining.iter().next() {
            remaining.remove(&start);
            let mut queue = VecDeque::from([start]);
            let mut component_indices = Vec::new();

            while let Some(idx) = queue.pop_front() {
                component_indices.push(idx);
                let candidate = &candidates[idx];
                let mut neighbor_coords = Vec::with_capacity(5);
                neighbor_coords.push((candidate.row, candidate.col));
                if let Some(row) = candidate.row.checked_sub(1) {
                    neighbor_coords.push((row, candidate.col));
                }
                neighbor_coords.push((candidate.row.saturating_add(1), candidate.col));
                if let Some(col) = candidate.col.checked_sub(1) {
                    neighbor_coords.push((candidate.row, col));
                }
                neighbor_coords.push((candidate.row, candidate.col.saturating_add(1)));

                for coord in neighbor_coords {
                    if let Some(indices) = coord_to_indices.get(&coord) {
                        for &neighbor in indices {
                            if remaining.remove(&neighbor) {
                                queue.push_back(neighbor);
                            }
                        }
                    }
                }
            }

            component_indices.sort_by_key(|idx| {
                let candidate = &candidates[*idx];
                (candidate.row, candidate.col, *idx)
            });
            components.push(
                component_indices
                    .into_iter()
                    .map(|idx| candidates[idx].clone())
                    .collect(),
            );
        }

        components
    }

    pub fn ingest_formula_batches(
        &mut self,
        batches: Vec<FormulaIngestBatch>,
    ) -> Result<FormulaIngestReport, ExcelError> {
        let formula_cells_seen = batches.iter().map(|batch| batch.len() as u64).sum();
        let (mut report, materialize_batches, planned_materialize) =
            match self.config.formula_plane_mode {
                FormulaPlaneMode::Off => (
                    FormulaIngestReport::with_mode(FormulaPlaneMode::Off),
                    batches,
                    BTreeMap::new(),
                ),
                FormulaPlaneMode::Shadow => (
                    self.analyze_formula_plane_shadow_candidates(&batches),
                    batches,
                    BTreeMap::new(),
                ),
                FormulaPlaneMode::AuthoritativeExperimental => {
                    self.analyze_formula_plane_authoritative_ingest(&batches)
                }
            };
        report.formula_cells_seen = formula_cells_seen;

        if !materialize_batches.iter().all(FormulaIngestBatch::is_empty)
            || !planned_materialize.is_empty()
        {
            let mut builder = self.begin_bulk_ingest();
            for batch in materialize_batches {
                if batch.is_empty() {
                    continue;
                }
                let sheet_id = builder.add_sheet(&batch.sheet_name);
                builder.add_formula_ids(
                    sheet_id,
                    batch
                        .formulas
                        .into_iter()
                        .map(|record| (record.row, record.col, record.ast_id)),
                );
            }
            for (sheet_name, formulas) in planned_materialize {
                if formulas.is_empty() {
                    continue;
                }
                let sheet_id = builder.add_sheet(&sheet_name);
                builder.add_formula_plans(sheet_id, formulas);
            }
            let summary = builder.finish()?;
            report.graph_formula_cells_materialized = summary.formulas as u64;
            report.graph_vertices_created = summary.vertices as u64;
            report.graph_edges_created = summary.edges as u64;
        }

        self.record_formula_ingest_report(report.clone());
        Ok(report)
    }

    pub fn handle_formula_parse_error(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        formula: &str,
        message: String,
    ) -> Result<Option<ASTNode>, ExcelError> {
        let policy = self.config.formula_parse_policy;

        if policy == FormulaParsePolicy::Strict {
            let col_a1 = col_letters_from_1based(col).unwrap_or_else(|_| "?".to_string());
            return Err(ExcelError::new(ExcelErrorKind::Value).with_message(format!(
                "Formula parse error at {sheet}!{col_a1}{row}: {message}"
            )));
        }

        self.formula_parse_diagnostics.push(FormulaParseDiagnostic {
            sheet: sheet.to_string(),
            row,
            col,
            formula: formula.to_string(),
            message: message.clone(),
            policy,
        });

        match policy {
            FormulaParsePolicy::Strict => unreachable!(),
            FormulaParsePolicy::KeepCachedValue => Ok(None),
            FormulaParsePolicy::AsText => Ok(Some(ASTNode::new(
                ASTNodeType::Literal(LiteralValue::Text(formula.to_string())),
                None,
            ))),
            FormulaParsePolicy::CoerceToError => {
                let err = ExcelError::new(ExcelErrorKind::Error)
                    .with_message(format!("Malformed formula: {message}"));
                Ok(Some(ASTNode::new(
                    ASTNodeType::Literal(LiteralValue::Error(err)),
                    None,
                )))
            }
        }
    }

    /// Build graph for all staged formulas.
    pub fn build_graph_all(&mut self) -> Result<(), formualizer_parse::ExcelError> {
        if self.staged_formulas.is_empty() {
            return Ok(());
        }
        // Take staged formulas before borrowing graph via builder.
        let staged = std::mem::take(&mut self.staged_formulas);
        for sheet in staged.keys() {
            let _ = self.add_sheet(sheet);
        }

        // Parse/recover first, then pass prepared batches through the centralized ingest seam.
        let mut prepared: PreparedFormulaBatches = Vec::new();
        for (sheet, entries) in staged {
            let mut formulas: Vec<FormulaIngestRecord> = Vec::new();
            let mut cache: rustc_hash::FxHashMap<String, Option<crate::engine::arena::AstNodeId>> =
                rustc_hash::FxHashMap::default();
            cache.reserve(4096);

            for (row, col, txt) in entries.into_entries() {
                let key = if txt.starts_with('=') {
                    txt
                } else {
                    format!("={txt}")
                };
                let ast_id = if let Some(cached) = cache.get(&key) {
                    *cached
                } else {
                    let parsed = match formualizer_parse::parser::parse(&key) {
                        Ok(parsed) => Some(parsed),
                        Err(e) => {
                            self.handle_formula_parse_error(&sheet, row, col, &key, e.to_string())?
                        }
                    };
                    let ast_id = parsed.as_ref().map(|ast| self.intern_formula_ast(ast));
                    cache.insert(key.clone(), ast_id);
                    ast_id
                };

                if let Some(ast_id) = ast_id {
                    formulas.push(FormulaIngestRecord::new(
                        row,
                        col,
                        ast_id,
                        Some(Arc::<str>::from(key.clone())),
                    ));
                }
            }

            if !formulas.is_empty() {
                prepared.push(FormulaIngestBatch::new(sheet, formulas));
            }
        }

        if !prepared.is_empty() {
            let _ = self.ingest_formula_batches(prepared)?;
        }
        Ok(())
    }

    /// Build graph for specific sheets (consuming only those staged entries).
    pub fn build_graph_for_sheets<'a, I: IntoIterator<Item = &'a str>>(
        &mut self,
        sheets: I,
    ) -> Result<(), formualizer_parse::ExcelError> {
        let mut collected: StagedFormulaBatches = Vec::new();
        for s in sheets {
            if let Some(entries) = self.staged_formulas.remove(s) {
                collected.push((s.to_string(), entries.into_entries()));
            }
        }

        if collected.is_empty() {
            return Ok(());
        }

        for (sheet, _) in &collected {
            let _ = self.add_sheet(sheet);
        }

        // Parse/recover first, then pass prepared batches through the centralized ingest seam.
        let mut prepared: PreparedFormulaBatches = Vec::new();
        let mut cache: rustc_hash::FxHashMap<String, Option<crate::engine::arena::AstNodeId>> =
            rustc_hash::FxHashMap::default();
        cache.reserve(4096);

        for (sheet, entries) in collected {
            let mut formulas: Vec<FormulaIngestRecord> = Vec::new();
            for (row, col, txt) in entries {
                let key = if txt.starts_with('=') {
                    txt
                } else {
                    format!("={txt}")
                };
                let ast_id = if let Some(cached) = cache.get(&key) {
                    *cached
                } else {
                    let parsed = match formualizer_parse::parser::parse(&key) {
                        Ok(parsed) => Some(parsed),
                        Err(e) => {
                            self.handle_formula_parse_error(&sheet, row, col, &key, e.to_string())?
                        }
                    };
                    let ast_id = parsed.as_ref().map(|ast| self.intern_formula_ast(ast));
                    cache.insert(key.clone(), ast_id);
                    ast_id
                };

                if let Some(ast_id) = ast_id {
                    formulas.push(FormulaIngestRecord::new(
                        row,
                        col,
                        ast_id,
                        Some(Arc::<str>::from(key.clone())),
                    ));
                }
            }
            if !formulas.is_empty() {
                prepared.push(FormulaIngestBatch::new(sheet, formulas));
            }
        }

        if !prepared.is_empty() {
            let _ = self.ingest_formula_batches(prepared)?;
        }
        Ok(())
    }

    /// Begin bulk Arrow ingest for base values (Phase A)
    pub fn begin_bulk_ingest_arrow(
        &mut self,
    ) -> crate::engine::arrow_ingest::ArrowBulkIngestBuilder<'_, R> {
        crate::engine::arrow_ingest::ArrowBulkIngestBuilder::new(self)
    }

    /// Begin bulk updates to Arrow store (Phase C)
    pub fn begin_bulk_update_arrow(
        &mut self,
    ) -> crate::engine::arrow_ingest::ArrowBulkUpdateBuilder<'_, R> {
        crate::engine::arrow_ingest::ArrowBulkUpdateBuilder::new(self)
    }

    fn ensure_known_sheet_id(&self, sheet: &str) -> Result<SheetId, crate::engine::EditorError> {
        self.graph.sheet_id(sheet).ok_or(
            crate::engine::graph::editor::vertex_editor::EditorError::InvalidName {
                name: sheet.to_string(),
                reason: "Unknown sheet".to_string(),
            },
        )
    }

    fn normalize_row_1based(row_1based: u32) -> Result<u32, crate::engine::EditorError> {
        if row_1based == 0 {
            return Err(crate::engine::EditorError::OutOfBounds { row: 0, col: 0 });
        }
        Ok(row_1based - 1)
    }

    fn normalize_row_range_1based(
        start_row_1based: u32,
        end_row_1based: u32,
    ) -> Result<(u32, u32), crate::engine::EditorError> {
        if start_row_1based == 0 || end_row_1based == 0 {
            return Err(crate::engine::EditorError::OutOfBounds { row: 0, col: 0 });
        }
        if start_row_1based > end_row_1based {
            return Err(crate::engine::EditorError::TransactionFailed {
                reason: "Row range start is greater than end".to_string(),
            });
        }
        Ok((start_row_1based - 1, end_row_1based - 1))
    }

    fn invalidate_row_visibility_mask_cache(&self) {
        if let Ok(mut cache) = self.row_visibility_mask_cache.write() {
            cache.clear();
        }
    }

    fn set_row_hidden_by_sheet_id(
        &mut self,
        sheet_id: SheetId,
        row0: u32,
        hidden: bool,
        source: RowVisibilitySource,
    ) -> bool {
        let changed = {
            let state = self.row_visibility.entry(sheet_id).or_default();
            state.set_row_hidden(row0, hidden, source)
        };

        let remove_entry = self
            .row_visibility
            .get(&sheet_id)
            .map(|state| state.is_empty())
            .unwrap_or(false);
        if remove_entry {
            self.row_visibility.remove(&sheet_id);
        }

        if changed {
            self.invalidate_row_visibility_mask_cache();
        }

        changed
    }

    fn set_rows_hidden_by_sheet_id(
        &mut self,
        sheet_id: SheetId,
        start_row0: u32,
        end_row0: u32,
        hidden: bool,
        source: RowVisibilitySource,
    ) -> bool {
        let changed = {
            let state = self.row_visibility.entry(sheet_id).or_default();
            state.set_rows_hidden(start_row0, end_row0, hidden, source)
        };

        let remove_entry = self
            .row_visibility
            .get(&sheet_id)
            .map(|state| state.is_empty())
            .unwrap_or(false);
        if remove_entry {
            self.row_visibility.remove(&sheet_id);
        }

        if changed {
            self.invalidate_row_visibility_mask_cache();
        }

        changed
    }

    fn shift_row_visibility_insert(&mut self, sheet_id: SheetId, before0: u32, count: u32) {
        if count == 0 {
            return;
        }
        let mut changed = false;
        let remove_entry = if let Some(state) = self.row_visibility.get_mut(&sheet_id) {
            changed = state.insert_rows(before0, count);
            state.is_empty()
        } else {
            false
        };
        if remove_entry {
            self.row_visibility.remove(&sheet_id);
        }
        if changed {
            self.invalidate_row_visibility_mask_cache();
        }
    }

    fn shift_row_visibility_delete(&mut self, sheet_id: SheetId, start0: u32, count: u32) {
        if count == 0 {
            return;
        }
        let mut changed = false;
        let remove_entry = if let Some(state) = self.row_visibility.get_mut(&sheet_id) {
            changed = state.delete_rows(start0, count);
            state.is_empty()
        } else {
            false
        };
        if remove_entry {
            self.row_visibility.remove(&sheet_id);
        }
        if changed {
            self.invalidate_row_visibility_mask_cache();
        }
    }

    fn apply_inverse_row_visibility_event(&mut self, event: &crate::engine::ChangeEvent) {
        if let crate::engine::ChangeEvent::SetRowVisibility {
            sheet_id,
            row0,
            source,
            old_hidden,
            ..
        } = event
        {
            let _ = self.set_row_hidden_by_sheet_id(*sheet_id, *row0, *old_hidden, *source);
        }
    }

    fn apply_forward_row_visibility_event(&mut self, event: &crate::engine::ChangeEvent) {
        if let crate::engine::ChangeEvent::SetRowVisibility {
            sheet_id,
            row0,
            source,
            new_hidden,
            ..
        } = event
        {
            let _ = self.set_row_hidden_by_sheet_id(*sheet_id, *row0, *new_hidden, *source);
        }
    }

    fn apply_inverse_row_visibility_events(&mut self, events: &[crate::engine::ChangeEvent]) {
        for event in events.iter().rev() {
            self.apply_inverse_row_visibility_event(event);
        }
    }

    fn apply_forward_row_visibility_events(&mut self, events: &[crate::engine::ChangeEvent]) {
        for event in events {
            self.apply_forward_row_visibility_event(event);
        }
    }

    fn apply_inverse_staged_formula_event(&mut self, event: &crate::engine::ChangeEvent) {
        if let crate::engine::ChangeEvent::StagedFormulaCellChanged {
            sheet,
            row,
            col,
            old,
            ..
        } = event
        {
            self.apply_staged_formula_cell(sheet, *row, *col, old.as_deref());
        }
    }

    fn apply_forward_staged_formula_event(&mut self, event: &crate::engine::ChangeEvent) {
        if let crate::engine::ChangeEvent::StagedFormulaCellChanged {
            sheet,
            row,
            col,
            new,
            ..
        } = event
        {
            self.apply_staged_formula_cell(sheet, *row, *col, new.as_deref());
        }
    }

    /// Set a single cell's staged formula text to `target` (clearing it when
    /// `None`). Used by undo/redo replay of per-cell staged-formula deltas.
    fn apply_staged_formula_cell(&mut self, sheet: &str, row: u32, col: u32, target: Option<&str>) {
        match target {
            Some(text) => self.stage_formula_text(sheet, row, col, text.to_string()),
            None => {
                self.clear_staged_formula_text(sheet, row, col);
            }
        }
    }

    pub fn set_row_hidden(
        &mut self,
        sheet: &str,
        row_1based: u32,
        hidden: bool,
        source: RowVisibilitySource,
    ) -> Result<(), crate::engine::EditorError> {
        let sheet_id = self.ensure_known_sheet_id(sheet)?;
        let row0 = Self::normalize_row_1based(row_1based)?;
        if self.set_row_hidden_by_sheet_id(sheet_id, row0, hidden, source) {
            self.record_formula_plane_structural_change(StructuralScope::Region(
                Region::whole_row(sheet_id, row0),
            ));
            self.mark_data_edited();
        }
        Ok(())
    }

    pub fn set_rows_hidden(
        &mut self,
        sheet: &str,
        start_row_1based: u32,
        end_row_1based: u32,
        hidden: bool,
        source: RowVisibilitySource,
    ) -> Result<(), crate::engine::EditorError> {
        let sheet_id = self.ensure_known_sheet_id(sheet)?;
        let (start_row0, end_row0) =
            Self::normalize_row_range_1based(start_row_1based, end_row_1based)?;
        if self.set_rows_hidden_by_sheet_id(sheet_id, start_row0, end_row0, hidden, source) {
            if start_row0 == end_row0 {
                self.record_formula_plane_structural_change(StructuralScope::Region(
                    Region::whole_row(sheet_id, start_row0),
                ));
            } else {
                self.record_formula_plane_structural_change(StructuralScope::Sheet(sheet_id));
            }
            self.mark_data_edited();
        }
        Ok(())
    }

    pub fn is_row_hidden(
        &self,
        sheet: &str,
        row_1based: u32,
        source: Option<RowVisibilitySource>,
    ) -> Option<bool> {
        let sheet_id = self.graph.sheet_id(sheet)?;
        let row0 = row_1based.checked_sub(1)?;
        Some(
            self.row_visibility
                .get(&sheet_id)
                .map(|state| state.is_row_hidden(row0, source))
                .unwrap_or(false),
        )
    }

    pub fn row_visibility_version(&self, sheet: &str) -> Option<u64> {
        let sheet_id = self.graph.sheet_id(sheet)?;
        Some(
            self.row_visibility
                .get(&sheet_id)
                .map(|state| state.version())
                .unwrap_or(0),
        )
    }

    fn build_row_visibility_mask_for_view(
        &self,
        view: &RangeView<'_>,
        mode: VisibilityMaskMode,
    ) -> Option<std::sync::Arc<arrow_array::BooleanArray>> {
        let sheet_rows = view.sheet().nrows as usize;
        if sheet_rows == 0 || view.start_row() >= sheet_rows {
            return Some(std::sync::Arc::new(arrow_array::BooleanArray::new_null(0)));
        }

        let sheet_id = self.graph.sheet_id(view.sheet_name())?;
        let start_row0 = view.start_row() as u32;
        let end_row0 = view.end_row().min(sheet_rows.saturating_sub(1)) as u32;
        let version = self
            .row_visibility
            .get(&sheet_id)
            .map(|state| state.version())
            .unwrap_or(0);
        let key = VisibilityMaskCacheKey {
            sheet_id,
            start_row0,
            end_row0,
            mode,
            version,
        };

        if let Ok(cache) = self.row_visibility_mask_cache.read()
            && let Some(mask) = cache.get(&key)
        {
            #[cfg(test)]
            visibility_mask_test_hooks::inc_hit();
            return Some(mask.clone());
        }

        #[cfg(test)]
        visibility_mask_test_hooks::inc_miss();

        let state = self.row_visibility.get(&sheet_id);
        let mut out = Vec::with_capacity((end_row0 - start_row0 + 1) as usize);
        for row0 in start_row0..=end_row0 {
            let manual_hidden = state
                .map(|s| s.is_row_hidden(row0, Some(RowVisibilitySource::Manual)))
                .unwrap_or(false);
            let filter_hidden = state
                .map(|s| s.is_row_hidden(row0, Some(RowVisibilitySource::Filter)))
                .unwrap_or(false);

            let include = match mode {
                VisibilityMaskMode::IncludeAll => true,
                VisibilityMaskMode::ExcludeManualHidden => !manual_hidden,
                VisibilityMaskMode::ExcludeFilterHidden => !filter_hidden,
                VisibilityMaskMode::ExcludeManualOrFilterHidden => {
                    !(manual_hidden || filter_hidden)
                }
            };
            out.push(include);
        }

        let mask = std::sync::Arc::new(arrow_array::BooleanArray::from(out));
        if let Ok(mut cache) = self.row_visibility_mask_cache.write() {
            const MAX_CACHE_ENTRIES: usize = 4096;
            if cache.len() >= MAX_CACHE_ENTRIES {
                cache.clear();
                #[cfg(test)]
                visibility_mask_test_hooks::inc_eviction();
            }
            cache.insert(key, mask.clone());
        }

        Some(mask)
    }

    fn editor_error_to_excel(error: crate::engine::EditorError) -> ExcelError {
        match error {
            crate::engine::EditorError::Excel(error) => error,
            other => ExcelError::new(ExcelErrorKind::Value).with_message(other.to_string()),
        }
    }

    fn demote_span_containing_cell_for_write(
        &mut self,
        sheet_id: SheetId,
        row0: u32,
        col0: u32,
    ) -> Result<(), crate::engine::EditorError> {
        if self.config.formula_plane_mode == FormulaPlaneMode::Off {
            return Ok(());
        }
        let placement = PlacementCoord::new(sheet_id, row0, col0);
        let inside_active_span = self
            .graph
            .formula_authority()
            .plane
            .spans
            .find_at(placement)
            .is_some();
        if inside_active_span {
            self.demote_spans_preserving_computed_overlays(
                sheet_id,
                Region::point(sheet_id, row0, col0),
            )?;
        }
        Ok(())
    }

    fn demote_spans_preserving_computed_overlays(
        &mut self,
        _sheet_id: SheetId,
        affected_region: Region,
    ) -> Result<(), crate::engine::EditorError> {
        // Per-cell write inside a span (or whole-sheet demote via remove_sheet):
        // not a structural axis shift. Demote every span whose result or read
        // region intersects `affected_region`; leave disjoint spans untouched.
        self.demote_spans_for_structural_op_impl(None, affected_region, false)
    }

    fn structural_row_region(sheet_id: SheetId, start_row0: u32) -> Region {
        Region::rows_from(sheet_id, start_row0)
    }

    fn structural_col_region(sheet_id: SheetId, start_col0: u32) -> Region {
        Region::cols_from(sheet_id, start_col0)
    }

    fn span_result_region_intersects_affected(
        span: &crate::formula_plane::runtime::FormulaSpan,
        affected_region: &Region,
    ) -> bool {
        Region::from_domain(span.result_region.domain()).intersects(affected_region)
    }

    fn span_any_read_region_intersects_affected(
        plane: &FormulaPlane,
        span: &crate::formula_plane::runtime::FormulaSpan,
        affected_region: &Region,
    ) -> bool {
        span.read_summary_id
            .and_then(|read_summary_id| plane.span_read_summaries.get(read_summary_id))
            .is_some_and(|summary| {
                summary
                    .dependencies
                    .iter()
                    .any(|dependency| dependency.read_region.intersects(affected_region))
            })
    }

    fn insert_formula_plane_dirty_coords_for_span(
        &self,
        span_ref: FormulaSpanRef,
        dirty: ProducerDirtyDomain,
        out: &mut FxHashSet<(SheetId, u32, u32)>,
    ) -> Result<(), crate::engine::EditorError> {
        let authority = self.graph.formula_authority();
        let span = authority.plane.spans.get(span_ref).ok_or_else(|| {
            ExcelError::new(ExcelErrorKind::NImpl)
                .with_message("FormulaPlane dirty transfer referenced a stale span")
        })?;
        match dirty {
            ProducerDirtyDomain::Whole => {
                out.extend(
                    span.domain
                        .iter()
                        .map(|coord| (coord.sheet_id, coord.row, coord.col)),
                );
            }
            ProducerDirtyDomain::Cells(cells) => {
                out.extend(cells.into_iter().filter_map(|key| {
                    let coord = PlacementCoord::new(key.sheet_id, key.row, key.col);
                    span.domain
                        .contains(coord)
                        .then_some((coord.sheet_id, coord.row, coord.col))
                }));
            }
            ProducerDirtyDomain::Regions(regions) => {
                out.extend(span.domain.iter().filter_map(|coord| {
                    let key = crate::formula_plane::region_index::RegionKey::from(coord);
                    regions
                        .iter()
                        .any(|region| region.contains_key(key))
                        .then_some((coord.sheet_id, coord.row, coord.col))
                }));
            }
        }
        Ok(())
    }

    fn compute_current_formula_plane_dirty_result_coords(
        &self,
    ) -> Result<FxHashSet<(SheetId, u32, u32)>, crate::engine::EditorError> {
        use crate::formula_plane::producer::compute_dirty_closure;

        let authority = self.graph.formula_authority();
        let span_refs = authority.active_span_refs();
        let span_refs_by_id = span_refs
            .iter()
            .copied()
            .map(|span_ref| (span_ref.id, span_ref))
            .collect::<BTreeMap<_, _>>();
        let mut dirty_coords = FxHashSet::default();

        if self.formula_plane_indexes_epoch_seen != authority.indexes_epoch() {
            for span_ref in span_refs {
                self.insert_formula_plane_dirty_coords_for_span(
                    span_ref,
                    ProducerDirtyDomain::Whole,
                    &mut dirty_coords,
                )?;
            }
            return Ok(dirty_coords);
        }

        let pending_changed_regions = authority.pending_changed_regions();
        if pending_changed_regions.is_empty() {
            return Ok(dirty_coords);
        }

        let closure = compute_dirty_closure(
            &authority.consumer_reads,
            pending_changed_regions.iter().copied(),
            |producer| authority.producer_results.producer_result_region(producer),
        );
        for work in closure.work {
            let FormulaProducerId::Span(span_id) = work.producer else {
                continue;
            };
            let Some(span_ref) = span_refs_by_id.get(&span_id).copied() else {
                continue;
            };
            self.insert_formula_plane_dirty_coords_for_span(
                span_ref,
                work.dirty,
                &mut dirty_coords,
            )?;
        }
        for fallback in closure.fallbacks {
            let FormulaProducerId::Span(span_id) = fallback.consumer else {
                continue;
            };
            let Some(span_ref) = span_refs_by_id.get(&span_id).copied() else {
                continue;
            };
            self.insert_formula_plane_dirty_coords_for_span(
                span_ref,
                ProducerDirtyDomain::Whole,
                &mut dirty_coords,
            )?;
        }

        Ok(dirty_coords)
    }

    /// Demote active FormulaPlane spans affected by a structural edit on `sheet_id`.
    ///
    /// This is the conservative Option-A correctness path for structural edits: rather than
    /// attempting to transform FormulaPlane span domains/templates/indexes, materialize each span
    /// placement as an ordinary legacy graph formula at its current coordinate, remove the span,
    /// and let the existing VertexEditor structural machinery shift/delete those vertices and
    /// adjust their ASTs.  Spans whose formula domain is on `sheet_id` are affected directly; spans
    /// on other sheets are also affected when one of their retained read regions targets
    /// `sheet_id`, because those read-region coordinates become stale after row/column shifts.
    fn demote_spans_for_structural_op(
        &mut self,
        op: StructuralOp,
        affected_region: Region,
    ) -> Result<(), crate::engine::EditorError> {
        if op.count() == 0 {
            return Ok(());
        }
        self.demote_spans_for_structural_op_impl(Some(op), affected_region, true)
    }

    fn demote_spans_for_structural_op_impl(
        &mut self,
        op: Option<StructuralOp>,
        affected_region: Region,
        clear_computed_overlays: bool,
    ) -> Result<(), crate::engine::EditorError> {
        struct SpanPlan {
            span_ref: FormulaSpanRef,
            sheet_id: SheetId,
            ast: ASTNode,
            origin_row: u32,
            origin_col: u32,
            binding_set_id: Option<crate::formula_plane::runtime::SpanBindingSetId>,
            placements: Vec<(u32, u32)>,
        }

        fn substitute_literal_slots_for_template_placement(
            ast: &ASTNode,
            binding: &[LiteralValue],
        ) -> ASTNode {
            fn clone_with_slots(
                ast: &ASTNode,
                binding: &[LiteralValue],
                next: &mut usize,
                in_array: bool,
            ) -> ASTNode {
                let node_type = match &ast.node_type {
                    ASTNodeType::Literal(_) if !in_array => {
                        let value = binding.get(*next).cloned().unwrap_or(LiteralValue::Empty);
                        *next = next.saturating_add(1);
                        ASTNodeType::Literal(value)
                    }
                    ASTNodeType::Literal(value) => ASTNodeType::Literal(value.clone()),
                    ASTNodeType::Reference {
                        original,
                        reference,
                    } => ASTNodeType::Reference {
                        original: original.clone(),
                        reference: reference.clone(),
                    },
                    ASTNodeType::UnaryOp { op, expr } => ASTNodeType::UnaryOp {
                        op: op.clone(),
                        expr: Box::new(clone_with_slots(expr, binding, next, in_array)),
                    },
                    ASTNodeType::BinaryOp { op, left, right } => ASTNodeType::BinaryOp {
                        op: op.clone(),
                        left: Box::new(clone_with_slots(left, binding, next, in_array)),
                        right: Box::new(clone_with_slots(right, binding, next, in_array)),
                    },
                    ASTNodeType::Function { name, args } => ASTNodeType::Function {
                        name: name.clone(),
                        args: args
                            .iter()
                            .map(|arg| clone_with_slots(arg, binding, next, in_array))
                            .collect(),
                    },
                    ASTNodeType::Call { callee, args } => ASTNodeType::Call {
                        callee: Box::new(clone_with_slots(callee, binding, next, in_array)),
                        args: args
                            .iter()
                            .map(|arg| clone_with_slots(arg, binding, next, in_array))
                            .collect(),
                    },
                    ASTNodeType::Array(rows) => ASTNodeType::Array(
                        rows.iter()
                            .map(|row| {
                                row.iter()
                                    .map(|cell| clone_with_slots(cell, binding, next, true))
                                    .collect()
                            })
                            .collect(),
                    ),
                };
                ASTNode::new(node_type, ast.source_token.clone())
            }
            let mut next = 0usize;
            clone_with_slots(ast, binding, &mut next, false)
        }

        let span_refs = self.graph.formula_authority().active_span_refs();
        if span_refs.is_empty() {
            return Ok(());
        }
        let dirty_span_coords = if clear_computed_overlays {
            FxHashSet::default()
        } else {
            self.compute_current_formula_plane_dirty_result_coords()?
        };

        struct ShiftPlan {
            span_ref: FormulaSpanRef,
            template_id: crate::formula_plane::ids::FormulaTemplateId,
            new_origin_row: u32,
            new_origin_col: u32,
            new_domain: crate::formula_plane::runtime::PlacementDomain,
            new_read_summary: Option<SpanReadSummary>,
            binding_set_id: Option<crate::formula_plane::runtime::SpanBindingSetId>,
            force_binding_residual_axes: bool,
        }

        fn checked_shift_u32(value: u32, delta: i64) -> Option<u32> {
            u32::try_from(i64::from(value).checked_add(delta)?).ok()
        }

        fn shifted_read_summary(
            read_summary: &SpanReadSummary,
            new_result_region: Region,
            op: StructuralOp,
            row_delta: i64,
            col_delta: i64,
        ) -> Option<SpanReadSummary> {
            let mut dependencies = Vec::with_capacity(read_summary.dependencies.len());
            for dependency in &read_summary.dependencies {
                let read_region = match op.classify_region(dependency.read_region) {
                    crate::formula_plane::structural_shift::AxisShiftCase::OtherSheet
                    | crate::formula_plane::structural_shift::AxisShiftCase::EntirelyBelow => {
                        dependency.read_region
                    }
                    crate::formula_plane::structural_shift::AxisShiftCase::EntirelyAboveShift {
                        ..
                    } => dependency
                        .read_region
                        .project_through_axis_shift(row_delta, col_delta)?,
                    crate::formula_plane::structural_shift::AxisShiftCase::Straddles
                    | crate::formula_plane::structural_shift::AxisShiftCase::DeleteFullyContains => {
                        return None;
                    }
                };
                dependencies.push(crate::formula_plane::producer::SpanReadDependency {
                    read_region,
                    projection: dependency.projection,
                });
            }
            Some(SpanReadSummary {
                result_region: new_result_region,
                dependencies,
            })
        }

        fn compact_axis_through_delete(
            min: u32,
            max: u32,
            start: u32,
            count: u32,
        ) -> Option<(u32, u32)> {
            let end = start.saturating_add(count);
            if max < start || min >= end {
                return Some((min.saturating_sub(count), max.saturating_sub(count)));
            }
            let keeps_left = min < start;
            let keeps_right = max >= end;
            match (keeps_left, keeps_right) {
                (false, false) => None,
                (true, false) => Some((min, start.checked_sub(1)?)),
                (false, true) => Some((start, max.checked_sub(count)?)),
                (true, true) => Some((min, max.checked_sub(count)?)),
            }
        }

        fn compact_domain_through_delete(
            domain: &PlacementDomain,
            op: StructuralOp,
        ) -> Option<PlacementDomain> {
            match (domain, op) {
                (
                    PlacementDomain::RowRun {
                        sheet_id,
                        row_start,
                        row_end,
                        col,
                    },
                    StructuralOp::DeleteRows { start, count, .. },
                ) => {
                    let (row_start, row_end) =
                        compact_axis_through_delete(*row_start, *row_end, start, count)?;
                    Some(PlacementDomain::row_run(
                        *sheet_id, row_start, row_end, *col,
                    ))
                }
                (
                    PlacementDomain::Rect {
                        sheet_id,
                        row_start,
                        row_end,
                        col_start,
                        col_end,
                    },
                    StructuralOp::DeleteRows { start, count, .. },
                ) => {
                    let (row_start, row_end) =
                        compact_axis_through_delete(*row_start, *row_end, start, count)?;
                    Some(PlacementDomain::rect(
                        *sheet_id, row_start, row_end, *col_start, *col_end,
                    ))
                }
                (
                    PlacementDomain::ColRun {
                        sheet_id,
                        row,
                        col_start,
                        col_end,
                    },
                    StructuralOp::DeleteColumns { start, count, .. },
                ) => {
                    let (col_start, col_end) =
                        compact_axis_through_delete(*col_start, *col_end, start, count)?;
                    Some(PlacementDomain::col_run(
                        *sheet_id, *row, col_start, col_end,
                    ))
                }
                (
                    PlacementDomain::Rect {
                        sheet_id,
                        row_start,
                        row_end,
                        col_start,
                        col_end,
                    },
                    StructuralOp::DeleteColumns { start, count, .. },
                ) => {
                    let (col_start, col_end) =
                        compact_axis_through_delete(*col_start, *col_end, start, count)?;
                    Some(PlacementDomain::rect(
                        *sheet_id, *row_start, *row_end, col_start, col_end,
                    ))
                }
                _ => None,
            }
        }

        fn compact_axis_range_through_delete(
            axis: crate::formula_plane::region_index::AxisRange,
            start: u32,
            count: u32,
        ) -> Option<crate::formula_plane::region_index::AxisRange> {
            use crate::formula_plane::region_index::AxisRange;
            match axis {
                AxisRange::Point(point) => compact_axis_through_delete(point, point, start, count)
                    .map(|(point, _)| AxisRange::Point(point)),
                AxisRange::Span(min, max) => compact_axis_through_delete(min, max, start, count)
                    .map(|(min, max)| AxisRange::Span(min, max)),
                AxisRange::All => Some(AxisRange::All),
                AxisRange::From(_) | AxisRange::To(_) => None,
            }
        }

        fn compact_region_through_delete(region: Region, op: StructuralOp) -> Option<Region> {
            let (rows, cols) = region.axis_ranges();
            match op {
                StructuralOp::DeleteRows {
                    sheet_id,
                    start,
                    count,
                } if region.sheet_id() == sheet_id => Some(Region {
                    sheet_id,
                    rows: compact_axis_range_through_delete(rows, start, count)?,
                    cols,
                }),
                StructuralOp::DeleteColumns {
                    sheet_id,
                    start,
                    count,
                } if region.sheet_id() == sheet_id => Some(Region {
                    sheet_id,
                    rows,
                    cols: compact_axis_range_through_delete(cols, start, count)?,
                }),
                _ => Some(region),
            }
        }

        fn compact_read_summary_through_delete(
            read_summary: &SpanReadSummary,
            new_result_region: Region,
            op: StructuralOp,
        ) -> Option<SpanReadSummary> {
            let mut dependencies = Vec::with_capacity(read_summary.dependencies.len());
            for dependency in &read_summary.dependencies {
                let read_region = match op.classify_region(dependency.read_region) {
                    crate::formula_plane::structural_shift::AxisShiftCase::OtherSheet
                    | crate::formula_plane::structural_shift::AxisShiftCase::EntirelyBelow => {
                        dependency.read_region
                    }
                    crate::formula_plane::structural_shift::AxisShiftCase::EntirelyAboveShift {
                        ..
                    } => {
                        let (row_delta, col_delta) = op.axis_shift_delta();
                        dependency
                            .read_region
                            .project_through_axis_shift(row_delta, col_delta)?
                    }
                    crate::formula_plane::structural_shift::AxisShiftCase::Straddles => {
                        compact_region_through_delete(dependency.read_region, op)?
                    }
                    crate::formula_plane::structural_shift::AxisShiftCase::DeleteFullyContains => {
                        return None;
                    }
                };
                dependencies.push(crate::formula_plane::producer::SpanReadDependency {
                    read_region,
                    projection: dependency.projection,
                });
            }
            Some(SpanReadSummary {
                result_region: new_result_region,
                dependencies,
            })
        }

        fn domain_origin_1_based(domain: &PlacementDomain) -> (u32, u32) {
            match domain {
                PlacementDomain::RowRun { row_start, col, .. } => (row_start + 1, col + 1),
                PlacementDomain::ColRun { row, col_start, .. } => (row + 1, col_start + 1),
                PlacementDomain::Rect {
                    row_start,
                    col_start,
                    ..
                } => (row_start + 1, col_start + 1),
            }
        }

        let mut shift_plans = Vec::new();
        let mut remove_refs = Vec::new();
        let mut demote_refs = Vec::new();
        for span_ref in span_refs {
            let authority = self.graph.formula_authority();
            let Some(span) = authority.plane.spans.get(span_ref) else {
                continue;
            };
            let read_summary = span
                .read_summary_id
                .and_then(|id| authority.plane.span_read_summaries.get(id));
            let Some(op) = op else {
                // Non-structural demote path (per-cell write into span, or
                // remove_sheet's whole-sheet sweep). Only demote spans whose
                // result or read region intersects affected_region; leave
                // disjoint spans untouched.
                let result_region_affected =
                    Self::span_result_region_intersects_affected(span, &affected_region);
                let read_region_affected = Self::span_any_read_region_intersects_affected(
                    &authority.plane,
                    span,
                    &affected_region,
                );
                if result_region_affected || read_region_affected {
                    demote_refs.push(span_ref);
                }
                continue;
            };
            match classify_span_for_op(span, read_summary, op) {
                SpanShiftPlan::NoOp => {}
                SpanShiftPlan::Remove => {
                    remove_refs.push(span_ref);
                }
                SpanShiftPlan::Demote {
                    reason:
                        crate::formula_plane::structural_shift::SpanDemoteReason::DeletePartiallyOverlaps,
                } => {
                    let binding_compaction_safe = span
                        .binding_set_id
                        .and_then(|id| authority.plane.binding_sets.get(id))
                        .is_none_or(|binding_set| binding_set.is_single_literal_binding());
                    if binding_compaction_safe
                        && let Some(new_domain) = compact_domain_through_delete(&span.domain, op)
                    {
                        let new_result_region = Region::from_domain(&new_domain);
                        let new_read_summary = if let Some(summary) = read_summary {
                            compact_read_summary_through_delete(summary, new_result_region, op)
                        } else {
                            None
                        };
                        if read_summary.is_none() || new_read_summary.is_some() {
                            let (new_origin_row, new_origin_col) = domain_origin_1_based(&new_domain);
                            let Some(template) = authority.plane.templates.get(span.template_id)
                            else {
                                return Err(ExcelError::new(ExcelErrorKind::Ref)
                                    .with_message(
                                        "FormulaPlane delete compaction found a span with a missing template",
                                    )
                                    .into());
                            };
                            let force_binding_residual_axes = span
                                .binding_set_id
                                .and_then(|id| authority.plane.binding_sets.get(id))
                                .is_some_and(|binding_set| {
                                    !binding_set.value_ref_slots.is_empty()
                                        && (new_origin_row != template.origin_row
                                            || new_origin_col != template.origin_col)
                                });
                            shift_plans.push(ShiftPlan {
                                span_ref,
                                template_id: span.template_id,
                                new_origin_row,
                                new_origin_col,
                                new_domain,
                                new_read_summary,
                                binding_set_id: span.binding_set_id,
                                force_binding_residual_axes,
                            });
                        } else {
                            demote_refs.push(span_ref);
                        }
                    } else {
                        demote_refs.push(span_ref);
                    }
                }
                SpanShiftPlan::Demote { .. } => {
                    demote_refs.push(span_ref);
                }
                SpanShiftPlan::Shift {
                    row_delta,
                    col_delta,
                    origin_row_delta,
                    origin_col_delta,
                } => {
                    let Some(template) = authority.plane.templates.get(span.template_id) else {
                        return Err(ExcelError::new(ExcelErrorKind::Ref)
                            .with_message("FormulaPlane shift found a span with a missing template")
                            .into());
                    };
                    let Some(new_origin_row) =
                        checked_shift_u32(template.origin_row, origin_row_delta)
                    else {
                        return Err(ExcelError::new(ExcelErrorKind::Ref)
                            .with_message("FormulaPlane shift overflowed template origin row")
                            .into());
                    };
                    let Some(new_origin_col) =
                        checked_shift_u32(template.origin_col, origin_col_delta)
                    else {
                        return Err(ExcelError::new(ExcelErrorKind::Ref)
                            .with_message("FormulaPlane shift overflowed template origin column")
                            .into());
                    };
                    let Some(new_domain) =
                        span.domain.project_through_axis_shift(row_delta, col_delta)
                    else {
                        return Err(ExcelError::new(ExcelErrorKind::Ref)
                            .with_message("FormulaPlane shift overflowed span domain")
                            .into());
                    };
                    let new_result_region = Region::from_domain(&new_domain);
                    let new_read_summary = if let Some(summary) = read_summary {
                        Some(
                            shifted_read_summary(
                                summary,
                                new_result_region,
                                op,
                                row_delta,
                                col_delta,
                            )
                            .ok_or_else(|| {
                                ExcelError::new(ExcelErrorKind::Ref).with_message(
                                    "FormulaPlane shift could not project read summary",
                                )
                            })?,
                        )
                    } else {
                        None
                    };
                    let force_binding_residual_axes = span
                        .binding_set_id
                        .and_then(|id| authority.plane.binding_sets.get(id))
                        .is_some_and(|binding_set| {
                            !binding_set.value_ref_slots.is_empty()
                                && (origin_row_delta != 0 || origin_col_delta != 0)
                        });
                    shift_plans.push(ShiftPlan {
                        span_ref,
                        template_id: span.template_id,
                        new_origin_row,
                        new_origin_col,
                        new_domain,
                        new_read_summary,
                        binding_set_id: span.binding_set_id,
                        force_binding_residual_axes,
                    });
                }
            }
        }
        if !shift_plans.is_empty() || !remove_refs.is_empty() {
            let authority = self.graph.formula_authority_mut();
            for span_ref in remove_refs {
                authority.plane.remove_overlays_for_source_span(span_ref);
                authority.plane.remove_span(span_ref);
            }
            for plan in shift_plans {
                let Some(template_id) = authority.plane.intern_shifted_template_origin(
                    plan.template_id,
                    plan.new_origin_row,
                    plan.new_origin_col,
                ) else {
                    return Err(ExcelError::new(ExcelErrorKind::Ref)
                        .with_message("FormulaPlane shift could not clone template origin")
                        .into());
                };
                if let Some(binding_set_id) = plan.binding_set_id {
                    let Some(template) = authority.plane.templates.get(template_id) else {
                        return Err(ExcelError::new(ExcelErrorKind::Ref)
                            .with_message("FormulaPlane shift could not find shifted template")
                            .into());
                    };
                    let (ast_id, origin_row, origin_col) =
                        (template.ast_id, template.origin_row, template.origin_col);
                    authority.plane.set_binding_template_anchor(
                        binding_set_id,
                        ast_id,
                        origin_row,
                        origin_col,
                    );
                }
                let read_summary_id = plan
                    .new_read_summary
                    .map(|summary| authority.plane.insert_span_read_summary(summary));
                let result_region = ResultRegion::scalar_cells(plan.new_domain.clone());
                if !authority.plane.replace_span_geometry(
                    plan.span_ref,
                    template_id,
                    plan.new_domain,
                    result_region,
                    read_summary_id,
                ) {
                    return Err(ExcelError::new(ExcelErrorKind::Ref)
                        .with_message("FormulaPlane shift could not update span geometry")
                        .into());
                }
                if plan.force_binding_residual_axes
                    && let Some(binding_set_id) = plan.binding_set_id
                {
                    // Value-ref memoization keys are placement-relative. When a
                    // structural op moves the formula origin while keeping some
                    // precedents fixed (e.g. insert a column before a formula
                    // family that reads column A), those keys no longer name
                    // the same producer cells. Keep correctness by forcing
                    // placement offsets into the key so memoization falls back
                    // to per-placement work rather than broadcasting stale
                    // representative values.
                    authority.plane.force_binding_residual_axes(binding_set_id);
                }
            }
            authority.rebuild_indexes();
            self.formula_plane_indexes_epoch_seen = 0;
        }

        let mut span_plans = Vec::new();
        for span_ref in demote_refs {
            let authority = self.graph.formula_authority();
            let Some(span) = authority.plane.spans.get(span_ref) else {
                continue;
            };
            let Some(template) = authority.plane.templates.get(span.template_id) else {
                return Err(ExcelError::new(ExcelErrorKind::Ref)
                    .with_message("FormulaPlane demotion found a span with a missing template")
                    .into());
            };
            let ast = self
                .graph
                .data_store()
                .retrieve_ast(template.ast_id, self.graph.sheet_reg())
                .ok_or_else(|| {
                    ExcelError::new(ExcelErrorKind::Ref)
                        .with_message("FormulaPlane demotion could not retrieve the template AST")
                })?;
            let placements = span
                .domain
                .iter()
                .map(|placement| (placement.row + 1, placement.col + 1))
                .collect();
            span_plans.push(SpanPlan {
                span_ref,
                sheet_id: span.sheet_id,
                ast,
                origin_row: template.origin_row,
                origin_col: template.origin_col,
                binding_set_id: span.binding_set_id,
                placements,
            });
        }
        if span_plans.is_empty() {
            return Ok(());
        }

        let mut relocated = Vec::new();
        let mut placement_cells = Vec::new();
        for plan in &span_plans {
            for &(row, col) in &plan.placements {
                let row_delta = i64::from(row) - i64::from(plan.origin_row);
                let col_delta = i64::from(col) - i64::from(plan.origin_col);
                let bound_ast = if let Some(binding_set_id) = plan.binding_set_id {
                    let authority = self.graph.formula_authority();
                    if let Some(binding_set) = authority.plane.binding_sets.get(binding_set_id) {
                        if binding_set.is_single_literal_binding() {
                            plan.ast.clone()
                        } else {
                            let placement = crate::formula_plane::runtime::PlacementCoord::new(
                                plan.sheet_id,
                                row.saturating_sub(1),
                                col.saturating_sub(1),
                            );
                            let binding =
                                authority.plane.spans.get(plan.span_ref).and_then(|span| {
                                    binding_set
                                        .literal_bindings_for_placement(&span.domain, placement)
                                });
                            if let Some(binding) = binding {
                                substitute_literal_slots_for_template_placement(
                                    &plan.ast,
                                    binding.as_ref(),
                                )
                            } else {
                                plan.ast.clone()
                            }
                        }
                    } else {
                        plan.ast.clone()
                    }
                } else {
                    plan.ast.clone()
                };
                let ast = relocate_ast_for_template_placement(&bound_ast, row_delta, col_delta)?;
                relocated.push((plan.sheet_id, row, col, ast));
                placement_cells.push((plan.sheet_id, row, col));
            }
        }
        let planned_by_sheet = {
            let mut pipeline = self.ingest_pipeline();
            let mut planned_by_sheet: BTreeMap<
                SheetId,
                Vec<(u32, u32, AstNodeId, DependencyPlanRow)>,
            > = BTreeMap::new();
            for (formula_sheet_id, row, col, ast) in relocated {
                let placement =
                    CellRef::new(formula_sheet_id, Coord::from_excel(row, col, true, true));
                let ingested =
                    pipeline.ingest_formula(FormulaAstInput::Tree(ast), placement, None)?;
                planned_by_sheet.entry(formula_sheet_id).or_default().push((
                    row,
                    col,
                    ingested.ast_id,
                    ingested.dep_plan,
                ));
            }
            planned_by_sheet
        };
        {
            let authority = self.graph.formula_authority_mut();
            for plan in &span_plans {
                authority
                    .plane
                    .remove_overlays_for_source_span(plan.span_ref);
                authority.plane.remove_span(plan.span_ref);
            }
            authority.rebuild_indexes();
        }
        if clear_computed_overlays {
            // Only clear placement cells whose coordinate intersects the affected
            // structural region. The structural-op contract preserves cells
            // BEFORE the structural boundary; the legacy `clear_computed_overlay_after_*`
            // call honors that. Demoting a span whose footprint straddles the
            // boundary still must not clear cells before the boundary, even
            // though the span as a whole is demoted.
            self.clear_computed_overlay_cells_in_region(&placement_cells, &affected_region);
        }
        for (formula_sheet_id, planned) in planned_by_sheet {
            let sheet_name = self.graph.sheet_name(formula_sheet_id).to_string();
            self.graph
                .bulk_set_formulas_with_plans(&sheet_name, planned)?;
        }
        if !clear_computed_overlays {
            for (formula_sheet_id, row, col) in &placement_cells {
                let row0 = row.saturating_sub(1);
                let col0 = col.saturating_sub(1);
                if dirty_span_coords.contains(&(*formula_sheet_id, row0, col0)) {
                    continue;
                }
                let cell =
                    CellRef::new(*formula_sheet_id, Coord::from_excel(*row, *col, true, true));
                if let Some(&vertex_id) = self.graph.get_vertex_id_for_address(&cell) {
                    self.graph.set_dirty(vertex_id, false);
                }
            }
        }
        self.formula_plane_indexes_epoch_seen = 0;
        Ok(())
    }

    /// Collect the [`FormulaSpanRef`]s for span producers the mixed scheduler
    /// reported as cycle members (gotcha G8, refs #112). These spans must be
    /// demoted to legacy so the cycle members are resolved on the legacy SCC
    /// path; see [`Self::demote_cyclic_spans`].
    fn collect_cyclic_span_refs(
        &self,
        schedule: &MixedSchedule,
        span_refs_by_id: &BTreeMap<FormulaSpanId, FormulaSpanRef>,
    ) -> Vec<FormulaSpanRef> {
        let mut refs = Vec::new();
        for fallback in &schedule.fallbacks {
            if fallback.reason != MixedScheduleFallbackReason::CycleDetected {
                continue;
            }
            if let FormulaProducerId::Span(span_id) = fallback.producer
                && let Some(span_ref) = span_refs_by_id.get(&span_id)
                && !refs.contains(span_ref)
            {
                refs.push(*span_ref);
            }
        }
        refs
    }

    /// Demote the given cyclic spans to legacy graph vertices so their member
    /// cells participate in the legacy Tarjan SCC pass (gotcha G8, refs #112).
    ///
    /// Reuses the non-structural demotion seam, which materializes each span's
    /// cells back onto the legacy graph and re-promotes any acyclic remainder
    /// that still forms a promotable run. We pass a `Region` that covers exactly
    /// the demote-target span domains so disjoint spans are left untouched.
    fn demote_cyclic_spans(&mut self, span_refs: &[FormulaSpanRef]) -> Result<(), ExcelError> {
        let mut regions: Vec<Region> = Vec::new();
        {
            let authority = self.graph.formula_authority();
            for span_ref in span_refs {
                if let Some(span) = authority.plane.spans.get(*span_ref) {
                    regions.push(Region::from_domain(&span.domain));
                }
            }
        }
        for region in regions {
            self.demote_spans_preserving_computed_overlays(region.sheet_id(), region)
                .map_err(|err| {
                    ExcelError::new(ExcelErrorKind::NImpl).with_message(format!(
                        "FormulaPlane cycle-member span demotion failed: {err:?}"
                    ))
                })?;
        }
        self.formula_plane_cycle_member_span_demotions = self
            .formula_plane_cycle_member_span_demotions
            .saturating_add(span_refs.len() as u64);
        // Mirror the demotion into the cumulative ingest report's fallback
        // histogram so cycle exclusions are visible like every other placement
        // fallback reason.
        Self::record_shadow_fallback_reason(
            &mut self.formula_ingest_report_total,
            PlacementFallbackReason::CycleMember,
            span_refs.len() as u64,
        );
        Ok(())
    }

    /// Evaluate residual *legacy-only* cyclic SCCs before the FormulaPlane
    /// mixed schedule runs (gotcha G8, refs #112).
    ///
    /// After cyclic spans are demoted to legacy ([`Self::demote_cyclic_spans`]),
    /// every cycle member is a graph vertex, so the cycle is now visible to the
    /// legacy Tarjan pass and lives entirely among legacy producers. The mixed
    /// schedule treats any cycle as not authoritative-safe; rather than abandon
    /// the surviving spans by falling through to a pure-legacy `evaluate_all`,
    /// stamp/evaluate just the cyclic SCC units here (`handle_cycle_unit` honors
    /// `CycleDetection::Static` vs `Runtime`), clear their dirty flags, and let
    /// the mixed schedule proceed cycle-free over the surviving spans plus the
    /// acyclic legacy work.
    ///
    /// Returns the number of cyclic SCC units that stamped at least one cell.
    fn evaluate_legacy_cycle_prepass(&mut self) -> Result<usize, ExcelError> {
        let dirty = self.graph.get_evaluation_vertices();
        if dirty.is_empty() {
            return Ok(0);
        }
        let (schedule, _vdeps, _meta) = self.create_evaluation_schedule(&dirty)?;
        let dirty_set: FxHashSet<VertexId> = dirty.iter().copied().collect();
        let mut cycle_errors = 0usize;
        let mut stamped_vertices: Vec<VertexId> = Vec::new();
        for &unit in &schedule.units {
            let ScheduleUnit::Cycle(i) = unit else {
                continue;
            };
            let members = schedule.unit_cycle(i);
            let stamped = self.handle_cycle_unit(members, None, Some(&dirty_set), None)?;
            if stamped > 0 {
                cycle_errors += 1;
            }
            stamped_vertices.extend(members.iter().copied());
        }
        // Clear dirty only on the cyclic members so the subsequent mixed
        // schedule no longer sees them as dirty legacy producers (which is what
        // surfaced the cycle). Acyclic legacy work stays dirty and is scheduled
        // normally alongside the surviving spans.
        if !stamped_vertices.is_empty() {
            self.graph.clear_dirty_flags(&stamped_vertices);
        }
        Ok(cycle_errors)
    }

    /// Insert rows (1-based) and mirror into Arrow store when enabled
    pub fn insert_rows(
        &mut self,
        sheet: &str,
        before: u32,
        count: u32,
    ) -> Result<crate::engine::graph::editor::vertex_editor::ShiftSummary, crate::engine::EditorError>
    {
        use crate::engine::graph::editor::vertex_editor::VertexEditor;
        let sheet_id = self.ensure_known_sheet_id(sheet)?;
        let before0 = before.saturating_sub(1);
        let affected_region = Self::structural_row_region(sheet_id, before0);
        let op = StructuralOp::InsertRows {
            sheet_id,
            before: before0,
            count,
        };
        self.demote_spans_for_structural_op(op, affected_region)?;
        let summary = {
            let mut editor = VertexEditor::new(&mut self.graph);
            editor.insert_rows(sheet_id, before0, count)?
        };
        if let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) {
            let before0 = before0 as usize;
            asheet.insert_rows(before0, count as usize);
        }
        self.mark_moved_formula_vertices_dirty(&summary);
        self.clear_computed_overlay_after_row(sheet, before0 as usize);
        self.shift_row_visibility_insert(sheet_id, before0, count);
        self.record_formula_plane_structural_change(StructuralScope::Region(affected_region));
        self.mark_topology_edited();
        Ok(summary)
    }

    /// Delete rows (1-based) and mirror into Arrow store when enabled
    pub fn delete_rows(
        &mut self,
        sheet: &str,
        start: u32,
        count: u32,
    ) -> Result<crate::engine::graph::editor::vertex_editor::ShiftSummary, crate::engine::EditorError>
    {
        use crate::engine::graph::editor::vertex_editor::VertexEditor;
        let sheet_id = self.ensure_known_sheet_id(sheet)?;
        let start0 = start.saturating_sub(1);
        let affected_region = Self::structural_row_region(sheet_id, start0);
        let op = StructuralOp::DeleteRows {
            sheet_id,
            start: start0,
            count,
        };
        self.demote_spans_for_structural_op(op, affected_region)?;
        let summary = {
            let mut editor = VertexEditor::new(&mut self.graph);
            editor.delete_rows(sheet_id, start0, count)?
        };
        if let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) {
            let start0 = start0 as usize;
            asheet.delete_rows(start0, count as usize);
        }
        self.mark_moved_formula_vertices_dirty(&summary);
        self.clear_computed_overlay_after_row(sheet, start0 as usize);
        self.shift_row_visibility_delete(sheet_id, start0, count);
        self.record_formula_plane_structural_change(StructuralScope::Region(affected_region));
        self.mark_topology_edited();
        Ok(summary)
    }

    /// Insert columns (1-based) and mirror into Arrow store when enabled
    pub fn insert_columns(
        &mut self,
        sheet: &str,
        before: u32,
        count: u32,
    ) -> Result<crate::engine::graph::editor::vertex_editor::ShiftSummary, crate::engine::EditorError>
    {
        use crate::engine::graph::editor::vertex_editor::VertexEditor;
        let sheet_id = self.graph.sheet_id(sheet).ok_or(
            crate::engine::graph::editor::vertex_editor::EditorError::InvalidName {
                name: sheet.to_string(),
                reason: "Unknown sheet".to_string(),
            },
        )?;
        let before0 = before.saturating_sub(1);
        let affected_region = Self::structural_col_region(sheet_id, before0);
        let op = StructuralOp::InsertColumns {
            sheet_id,
            before: before0,
            count,
        };
        self.demote_spans_for_structural_op(op, affected_region)?;
        let summary = {
            let mut editor = VertexEditor::new(&mut self.graph);
            editor.insert_columns(sheet_id, before0, count)?
        };
        if let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) {
            let before0 = before0 as usize;
            asheet.insert_columns(before0, count as usize);
        }
        self.mark_moved_formula_vertices_dirty(&summary);
        self.clear_computed_overlay_after_col(sheet, before0 as usize);
        self.record_formula_plane_structural_change(StructuralScope::Region(affected_region));
        self.mark_topology_edited();
        Ok(summary)
    }

    /// Delete columns (1-based) and mirror into Arrow store when enabled
    pub fn delete_columns(
        &mut self,
        sheet: &str,
        start: u32,
        count: u32,
    ) -> Result<crate::engine::graph::editor::vertex_editor::ShiftSummary, crate::engine::EditorError>
    {
        use crate::engine::graph::editor::vertex_editor::VertexEditor;
        let sheet_id = self.graph.sheet_id(sheet).ok_or(
            crate::engine::graph::editor::vertex_editor::EditorError::InvalidName {
                name: sheet.to_string(),
                reason: "Unknown sheet".to_string(),
            },
        )?;
        let start0 = start.saturating_sub(1);
        let affected_region = Self::structural_col_region(sheet_id, start0);
        let op = StructuralOp::DeleteColumns {
            sheet_id,
            start: start0,
            count,
        };
        self.demote_spans_for_structural_op(op, affected_region)?;
        let summary = {
            let mut editor = VertexEditor::new(&mut self.graph);
            editor.delete_columns(sheet_id, start0, count)?
        };
        if let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) {
            let start0 = start0 as usize;
            asheet.delete_columns(start0, count as usize);
        }
        self.mark_moved_formula_vertices_dirty(&summary);
        self.clear_computed_overlay_after_col(sheet, start0 as usize);
        self.record_formula_plane_structural_change(StructuralScope::Region(affected_region));
        self.mark_topology_edited();
        Ok(summary)
    }
    /// Arrow-backed used row bounds across a column span (1-based inclusive cols).
    fn arrow_used_row_bounds(
        &self,
        sheet: &str,
        start_col: u32,
        end_col: u32,
    ) -> Option<(u32, u32)> {
        let a = self.sheet_store().sheet(sheet)?;
        if a.columns.is_empty() {
            return None;
        }
        let sc0 = start_col.saturating_sub(1) as usize;
        let ec0 = end_col.saturating_sub(1) as usize;
        let col_hi = a.columns.len().saturating_sub(1);
        if sc0 > col_hi {
            return None;
        }
        let ec0 = ec0.min(col_hi);
        // Pass-scoped cache with snapshot guard
        let snap = self.data_snapshot_id();
        let mut min_r0: Option<usize> = None;
        for ci in sc0..=ec0 {
            let sheet_id = self.graph.sheet_id(sheet)?;
            if let Some((Some(mv), _)) = self.row_bounds_cache.read().ok().and_then(|g| {
                g.as_ref()
                    .and_then(|c| c.get_row_bounds(sheet_id, ci, snap))
            }) {
                let mv = mv as usize;
                min_r0 = Some(min_r0.map(|m| m.min(mv)).unwrap_or(mv));
                continue;
            }
            // Compute and store
            let (min_c, max_c) = Self::scan_column_used_bounds(a, ci);
            if let Ok(mut g) = self.row_bounds_cache.write() {
                g.get_or_insert_with(|| RowBoundsCache::new(snap))
                    .put_row_bounds(sheet_id, ci, snap, (min_c, max_c));
            }
            if let Some(m) = min_c {
                min_r0 = Some(min_r0.map(|mm| mm.min(m as usize)).unwrap_or(m as usize));
            }
        }
        min_r0?;
        let mut max_r0: Option<usize> = None;
        for ci in sc0..=ec0 {
            let sheet_id = self.graph.sheet_id(sheet)?;
            if let Some((_, Some(mv))) = self.row_bounds_cache.read().ok().and_then(|g| {
                g.as_ref()
                    .and_then(|c| c.get_row_bounds(sheet_id, ci, snap))
            }) {
                let mv = mv as usize;
                max_r0 = Some(max_r0.map(|m| m.max(mv)).unwrap_or(mv));
                continue;
            }
            let (_min_c, max_c) = Self::scan_column_used_bounds(a, ci);
            if let Ok(mut g) = self.row_bounds_cache.write() {
                g.get_or_insert_with(|| RowBoundsCache::new(snap))
                    .put_row_bounds(sheet_id, ci, snap, (_min_c, max_c));
            }
            if let Some(m) = max_c {
                max_r0 = Some(max_r0.map(|mm| mm.max(m as usize)).unwrap_or(m as usize));
            }
        }
        match (min_r0, max_r0) {
            (Some(a0), Some(b0)) => Some(((a0 as u32) + 1, (b0 as u32) + 1)),
            _ => None,
        }
    }

    fn scan_column_used_bounds(
        a: &crate::arrow_store::ArrowSheet,
        ci: usize,
    ) -> (Option<u32>, Option<u32>) {
        let col = &a.columns[ci];

        // Min: scan dense chunks first, then sparse chunks in ascending index order.
        let mut min_r0: Option<u32> = None;
        for (chunk_idx, chunk) in col.chunks.iter().enumerate() {
            let tags = chunk.type_tag.values();
            for (off, &t) in tags.iter().enumerate() {
                let overlay_non_empty = chunk
                    .overlay
                    .get(off)
                    .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                    .unwrap_or(false)
                    || chunk
                        .computed_overlay
                        .get(off)
                        .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                        .unwrap_or(false);
                if overlay_non_empty || t != crate::arrow_store::TypeTag::Empty as u8 {
                    let Some(&chunk_start) = a.chunk_starts.get(chunk_idx) else {
                        break;
                    };
                    let row0 = chunk_start + off;
                    min_r0 = Some(row0 as u32);
                    break;
                }
            }
            if min_r0.is_some() {
                break;
            }
        }
        if min_r0.is_none() && !col.sparse_chunks.is_empty() {
            let mut sparse_idxs: Vec<usize> = col.sparse_chunks.keys().copied().collect();
            sparse_idxs.sort_unstable();
            for chunk_idx in sparse_idxs {
                let Some(chunk) = col.sparse_chunks.get(&chunk_idx) else {
                    continue;
                };
                let Some(&chunk_start) = a.chunk_starts.get(chunk_idx) else {
                    continue;
                };
                let tags = chunk.type_tag.values();
                for (off, &t) in tags.iter().enumerate() {
                    let overlay_non_empty = chunk
                        .overlay
                        .get(off)
                        .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                        .unwrap_or(false)
                        || chunk
                            .computed_overlay
                            .get(off)
                            .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                            .unwrap_or(false);
                    if overlay_non_empty || t != crate::arrow_store::TypeTag::Empty as u8 {
                        let row0 = chunk_start + off;
                        min_r0 = Some(row0 as u32);
                        break;
                    }
                }
                if min_r0.is_some() {
                    break;
                }
            }
        }

        // Max: scan sparse chunks in descending index order, then dense chunks in reverse.
        let mut max_r0: Option<u32> = None;
        if !col.sparse_chunks.is_empty() {
            let mut sparse_idxs: Vec<usize> = col.sparse_chunks.keys().copied().collect();
            sparse_idxs.sort_unstable_by(|a, b| b.cmp(a));
            for chunk_idx in sparse_idxs {
                let Some(chunk) = col.sparse_chunks.get(&chunk_idx) else {
                    continue;
                };
                let Some(&chunk_start) = a.chunk_starts.get(chunk_idx) else {
                    continue;
                };
                let tags = chunk.type_tag.values();
                for (rev_idx, &t) in tags.iter().enumerate().rev() {
                    let overlay_non_empty = chunk
                        .overlay
                        .get(rev_idx)
                        .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                        .unwrap_or(false)
                        || chunk
                            .computed_overlay
                            .get(rev_idx)
                            .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                            .unwrap_or(false);
                    if overlay_non_empty || t != crate::arrow_store::TypeTag::Empty as u8 {
                        let row0 = chunk_start + rev_idx;
                        max_r0 = Some(row0 as u32);
                        break;
                    }
                }
                if max_r0.is_some() {
                    break;
                }
            }
        }
        if max_r0.is_none() {
            for (chunk_idx, chunk) in col.chunks.iter().enumerate().rev() {
                let tags = chunk.type_tag.values();
                for (rev_idx, &t) in tags.iter().enumerate().rev() {
                    let overlay_non_empty = chunk
                        .overlay
                        .get(rev_idx)
                        .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                        .unwrap_or(false)
                        || chunk
                            .computed_overlay
                            .get(rev_idx)
                            .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                            .unwrap_or(false);
                    if overlay_non_empty || t != crate::arrow_store::TypeTag::Empty as u8 {
                        let Some(&chunk_start) = a.chunk_starts.get(chunk_idx) else {
                            break;
                        };
                        let row0 = chunk_start + rev_idx;
                        max_r0 = Some(row0 as u32);
                        break;
                    }
                }
                if max_r0.is_some() {
                    break;
                }
            }
        }

        (min_r0, max_r0)
    }

    /// Arrow-backed used column bounds across a row span (1-based inclusive rows).
    fn arrow_used_col_bounds(
        &self,
        sheet: &str,
        start_row: u32,
        end_row: u32,
    ) -> Option<(u32, u32)> {
        let a = self.sheet_store().sheet(sheet)?;
        if a.columns.is_empty() {
            return None;
        }
        let sr0 = start_row.saturating_sub(1) as usize;
        let er0 = end_row.saturating_sub(1) as usize;
        if sr0 > er0 {
            return None;
        }
        // Map start/end rows into chunk ranges
        // We will scan each column for any non-empty within [sr0..=er0]
        let mut min_c0: Option<usize> = None;
        let mut max_c0: Option<usize> = None;
        // Precompute chunk bounds for row range
        for (ci, col) in a.columns.iter().enumerate() {
            let mut any_in_range = false;

            let scan_chunk = |chunk_idx: usize, chunk: &crate::arrow_store::ColumnChunk| -> bool {
                let Some(&chunk_start) = a.chunk_starts.get(chunk_idx) else {
                    return false;
                };
                let chunk_len = chunk.type_tag.len();
                if chunk_len == 0 {
                    return false;
                }
                let chunk_end = chunk_start + chunk_len.saturating_sub(1);
                // check intersection
                if sr0 > chunk_end || er0 < chunk_start {
                    return false;
                }
                let start_off = sr0.max(chunk_start) - chunk_start;
                let end_off = er0.min(chunk_end) - chunk_start;
                let tags = chunk.type_tag.values();
                for off in start_off..=end_off {
                    let overlay_non_empty = chunk
                        .overlay
                        .get(off)
                        .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                        .unwrap_or(false)
                        || chunk
                            .computed_overlay
                            .get(off)
                            .map(|ov| !matches!(ov, crate::arrow_store::OverlayValue::Empty))
                            .unwrap_or(false);
                    if overlay_non_empty || tags[off] != crate::arrow_store::TypeTag::Empty as u8 {
                        return true;
                    }
                }
                false
            };

            for (chunk_idx, chunk) in col.chunks.iter().enumerate() {
                if scan_chunk(chunk_idx, chunk) {
                    any_in_range = true;
                    break;
                }
            }

            if !any_in_range && !col.sparse_chunks.is_empty() {
                for (&chunk_idx, chunk) in col.sparse_chunks.iter() {
                    if scan_chunk(chunk_idx, chunk) {
                        any_in_range = true;
                        break;
                    }
                }
            }

            if any_in_range {
                min_c0 = Some(min_c0.map(|m| m.min(ci)).unwrap_or(ci));
                max_c0 = Some(max_c0.map(|m| m.max(ci)).unwrap_or(ci));
            }
        }
        match (min_c0, max_c0) {
            (Some(a0), Some(b0)) => Some(((a0 as u32) + 1, (b0 as u32) + 1)),
            _ => None,
        }
    }

    fn formula_row_bounds_for_columns(
        &self,
        sheet: &str,
        start_col: u32,
        end_col: u32,
    ) -> Option<(u32, u32)> {
        let sheet_id = self.graph.sheet_id(sheet)?;
        let sc0 = start_col.saturating_sub(1);
        let ec0 = end_col.saturating_sub(1);
        let mut min_r0: Option<u32> = None;
        let mut max_r0: Option<u32> = None;

        if let Some(index) = self.graph.sheet_index(sheet_id) {
            for vid in index.vertices_in_col_range(sc0, ec0) {
                if !matches!(
                    self.graph.get_vertex_kind(vid),
                    VertexKind::FormulaScalar | VertexKind::FormulaArray
                ) {
                    continue;
                }
                let row0 = self.graph.vertex_coord(vid).row();
                min_r0 = Some(min_r0.map(|m| m.min(row0)).unwrap_or(row0));
                max_r0 = Some(max_r0.map(|m| m.max(row0)).unwrap_or(row0));
            }
        } else {
            for vid in self.graph.vertices_in_sheet(sheet_id) {
                if !matches!(
                    self.graph.get_vertex_kind(vid),
                    VertexKind::FormulaScalar | VertexKind::FormulaArray
                ) {
                    continue;
                }
                let coord = self.graph.vertex_coord(vid);
                let col0 = coord.col();
                if col0 < sc0 || col0 > ec0 {
                    continue;
                }
                let row0 = coord.row();
                min_r0 = Some(min_r0.map(|m| m.min(row0)).unwrap_or(row0));
                max_r0 = Some(max_r0.map(|m| m.max(row0)).unwrap_or(row0));
            }
        }

        match (min_r0, max_r0) {
            (Some(a0), Some(b0)) => Some((a0 + 1, b0 + 1)),
            _ => None,
        }
    }

    fn formula_col_bounds_for_rows(
        &self,
        sheet: &str,
        start_row: u32,
        end_row: u32,
    ) -> Option<(u32, u32)> {
        let sheet_id = self.graph.sheet_id(sheet)?;
        let sr0 = start_row.saturating_sub(1);
        let er0 = end_row.saturating_sub(1);
        let mut min_c0: Option<u32> = None;
        let mut max_c0: Option<u32> = None;

        if let Some(index) = self.graph.sheet_index(sheet_id) {
            for vid in index.vertices_in_row_range(sr0, er0) {
                if !matches!(
                    self.graph.get_vertex_kind(vid),
                    VertexKind::FormulaScalar | VertexKind::FormulaArray
                ) {
                    continue;
                }
                let col0 = self.graph.vertex_coord(vid).col();
                min_c0 = Some(min_c0.map(|m| m.min(col0)).unwrap_or(col0));
                max_c0 = Some(max_c0.map(|m| m.max(col0)).unwrap_or(col0));
            }
        } else {
            for vid in self.graph.vertices_in_sheet(sheet_id) {
                if !matches!(
                    self.graph.get_vertex_kind(vid),
                    VertexKind::FormulaScalar | VertexKind::FormulaArray
                ) {
                    continue;
                }
                let coord = self.graph.vertex_coord(vid);
                let row0 = coord.row();
                if row0 < sr0 || row0 > er0 {
                    continue;
                }
                let col0 = coord.col();
                min_c0 = Some(min_c0.map(|m| m.min(col0)).unwrap_or(col0));
                max_c0 = Some(max_c0.map(|m| m.max(col0)).unwrap_or(col0));
            }
        }

        match (min_c0, max_c0) {
            (Some(a0), Some(b0)) => Some((a0 + 1, b0 + 1)),
            _ => None,
        }
    }

    fn union_used_bounds(
        first: Option<(u32, u32)>,
        second: Option<(u32, u32)>,
    ) -> Option<(u32, u32)> {
        match (first, second) {
            (Some((a0, b0)), Some((a1, b1))) => Some((a0.min(a1), b0.max(b1))),
            (Some(bounds), None) | (None, Some(bounds)) => Some(bounds),
            (None, None) => None,
        }
    }

    /// Mirror a single cell value into the Arrow overlay if enabled.
    /// Handles capacity growth, per-chunk overlay set, and heuristic compaction.
    fn mirror_value_to_overlay(&mut self, sheet: &str, row: u32, col: u32, value: &LiteralValue) {
        if !(self.config.arrow_storage_enabled && self.config.delta_overlay_enabled) {
            return;
        }
        if self.arrow_sheets.sheet(sheet).is_none() {
            self.arrow_sheets
                .sheets
                .push(crate::arrow_store::ArrowSheet {
                    name: std::sync::Arc::<str>::from(sheet),
                    columns: Vec::new(),
                    nrows: 0,
                    chunk_starts: Vec::new(),
                    chunk_rows: 32 * 1024,
                });
        }

        let row0 = row.saturating_sub(1) as usize;
        let col0 = col.saturating_sub(1) as usize;

        let asheet = self
            .arrow_sheets
            .sheet_mut(sheet)
            .expect("ArrowSheet must exist");

        let cur_cols = asheet.columns.len();
        if col0 >= cur_cols {
            asheet.insert_columns(cur_cols, (col0 + 1) - cur_cols);
        }

        if row0 >= asheet.nrows as usize {
            if asheet.columns.is_empty() {
                asheet.insert_columns(0, 1);
            }
            asheet.ensure_row_capacity(row0 + 1);
        }
        if let Some((ch_idx, in_off)) = asheet.chunk_of_row(row0) {
            use crate::arrow_store::OverlayValue;
            let ov = match value {
                LiteralValue::Empty => OverlayValue::Empty,
                LiteralValue::Int(i) => OverlayValue::Number(*i as f64),
                LiteralValue::Number(n) => OverlayValue::Number(*n),
                LiteralValue::Boolean(b) => OverlayValue::Boolean(*b),
                LiteralValue::Text(s) => OverlayValue::Text(std::sync::Arc::from(s.clone())),
                LiteralValue::Error(e) => {
                    OverlayValue::Error(crate::arrow_store::map_error_code(e.kind))
                }
                LiteralValue::Date(d) => {
                    let dt = d.and_hms_opt(0, 0, 0).unwrap();
                    let serial = crate::builtins::datetime::datetime_to_serial_for(
                        self.config.date_system,
                        &dt,
                    );
                    OverlayValue::DateTime(serial)
                }
                LiteralValue::DateTime(dt) => {
                    let serial = crate::builtins::datetime::datetime_to_serial_for(
                        self.config.date_system,
                        dt,
                    );
                    OverlayValue::DateTime(serial)
                }
                LiteralValue::Time(t) => {
                    let serial = t.num_seconds_from_midnight() as f64 / 86_400.0;
                    OverlayValue::DateTime(serial)
                }
                LiteralValue::Duration(d) => {
                    let serial = d.num_seconds() as f64 / 86_400.0;
                    OverlayValue::Duration(serial)
                }
                LiteralValue::Pending => OverlayValue::Pending,
                LiteralValue::Array(_) => OverlayValue::Error(crate::arrow_store::map_error_code(
                    formualizer_common::ExcelErrorKind::Value,
                )),
            };
            let computed_delta = if let Some(ch) = asheet.ensure_column_chunk_mut(col0, ch_idx) {
                let _ = ch.overlay.set(in_off, ov);
                // A user edit must invalidate any computed (formula/spill) overlay entry at
                // this cell. Otherwise, if the delta overlay later compacts into the base lanes
                // (clearing `overlay`), a stale `computed_overlay=Empty` could incorrectly mask
                // the edited base value under the read cascade.
                ch.computed_overlay.remove(in_off)
            } else {
                return;
            };
            // Heuristic compaction: > len/50 or > 1024
            let abs_threshold = 1024usize;
            let frac_den = 50usize;
            let freed = asheet.maybe_compact_chunk(col0, ch_idx, abs_threshold, frac_den);
            if freed > 0 {
                self.overlay_compactions = self.overlay_compactions.saturating_add(1);
            }
            self.adjust_computed_overlay_bytes(computed_delta);
        }
    }

    /// Remove a delta-overlay entry for a single cell (if present).
    ///
    /// This is used when transitioning a cell to a formula so that any previous user-edit overlay
    /// does not continue to mask computed overlay outputs.
    fn clear_delta_overlay_cell(&mut self, sheet: &str, row: u32, col: u32) {
        if !(self.config.arrow_storage_enabled && self.config.delta_overlay_enabled) {
            return;
        }
        let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) else {
            return;
        };
        let row0 = row.saturating_sub(1) as usize;
        let col0 = col.saturating_sub(1) as usize;
        if row0 >= asheet.nrows as usize {
            return;
        }
        if col0 >= asheet.columns.len() {
            return;
        }
        let Some((ch_idx, in_off)) = asheet.chunk_of_row(row0) else {
            return;
        };
        if let Some(ch) = asheet.columns[col0].chunk_mut(ch_idx) {
            let _ = ch.overlay.remove(in_off);
        }
    }

    fn clear_computed_overlay_col_row_range(
        &mut self,
        sheet: &str,
        col0: usize,
        start_row0: usize,
        end_row0_exclusive: usize,
    ) {
        if !(self.config.arrow_storage_enabled && self.config.write_formula_overlay_enabled) {
            return;
        }
        if start_row0 >= end_row0_exclusive {
            return;
        }

        let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) else {
            return;
        };
        if col0 >= asheet.columns.len() || start_row0 >= asheet.nrows as usize {
            return;
        }
        let end_row0_exclusive = end_row0_exclusive.min(asheet.nrows as usize);
        if start_row0 >= end_row0_exclusive {
            return;
        }

        let starts = asheet.chunk_starts.clone();
        let nrows = asheet.nrows as usize;
        let mut delta = 0isize;
        let Some(col) = asheet.columns.get_mut(col0) else {
            return;
        };
        for (chunk_idx, ch) in col.chunks.iter_mut().enumerate() {
            let Some(&chunk_start) = starts.get(chunk_idx) else {
                continue;
            };
            let chunk_end = starts
                .get(chunk_idx + 1)
                .copied()
                .unwrap_or(nrows)
                .min(chunk_start.saturating_add(ch.len()));
            let clear_start = start_row0.max(chunk_start);
            let clear_end = end_row0_exclusive.min(chunk_end);
            if clear_start >= clear_end {
                continue;
            }
            if clear_start == chunk_start && clear_end == chunk_end {
                delta = delta.saturating_sub(ch.computed_overlay.clear() as isize);
            } else {
                let start_in_chunk = clear_start.saturating_sub(chunk_start).min(ch.len());
                let end_in_chunk = clear_end.saturating_sub(chunk_start).min(ch.len());
                delta = delta.saturating_add(
                    ch.computed_overlay
                        .remove_range(start_in_chunk..end_in_chunk),
                );
            }
        }
        for (chunk_idx, ch) in &mut col.sparse_chunks {
            let Some(&chunk_start) = starts.get(*chunk_idx) else {
                continue;
            };
            let chunk_end = starts
                .get(*chunk_idx + 1)
                .copied()
                .unwrap_or(nrows)
                .min(chunk_start.saturating_add(ch.len()));
            let clear_start = start_row0.max(chunk_start);
            let clear_end = end_row0_exclusive.min(chunk_end);
            if clear_start >= clear_end {
                continue;
            }
            if clear_start == chunk_start && clear_end == chunk_end {
                delta = delta.saturating_sub(ch.computed_overlay.clear() as isize);
            } else {
                let start_in_chunk = clear_start.saturating_sub(chunk_start).min(ch.len());
                let end_in_chunk = clear_end.saturating_sub(chunk_start).min(ch.len());
                delta = delta.saturating_add(
                    ch.computed_overlay
                        .remove_range(start_in_chunk..end_in_chunk),
                );
            }
        }
        self.adjust_computed_overlay_bytes(delta);
    }

    fn clear_computed_overlay_cells_in_region(
        &mut self,
        cells: &[(SheetId, u32, u32)],
        affected_region: &Region,
    ) {
        let mut by_col: BTreeMap<(SheetId, u32), Vec<u32>> = BTreeMap::new();
        for (formula_sheet_id, row, col) in cells {
            let row0 = row.saturating_sub(1);
            let col0 = col.saturating_sub(1);
            let placement_region = Region::point(*formula_sheet_id, row0, col0);
            if placement_region.intersects(affected_region) {
                by_col
                    .entry((*formula_sheet_id, col0))
                    .or_default()
                    .push(row0);
            }
        }

        for ((formula_sheet_id, col0), mut rows) in by_col {
            rows.sort_unstable();
            rows.dedup();
            let sheet_name = self.graph.sheet_name(formula_sheet_id).to_string();
            let mut start = rows[0];
            let mut prev = rows[0];
            for row in rows.into_iter().skip(1) {
                if row == prev.saturating_add(1) {
                    prev = row;
                    continue;
                }
                self.clear_computed_overlay_col_row_range(
                    &sheet_name,
                    col0 as usize,
                    start as usize,
                    prev.saturating_add(1) as usize,
                );
                start = row;
                prev = row;
            }
            self.clear_computed_overlay_col_row_range(
                &sheet_name,
                col0 as usize,
                start as usize,
                prev.saturating_add(1) as usize,
            );
        }
    }

    fn clear_computed_overlay_after_row(&mut self, sheet: &str, start_row0: usize) {
        if !(self.config.arrow_storage_enabled && self.config.write_formula_overlay_enabled) {
            return;
        }

        let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) else {
            return;
        };
        if start_row0 >= asheet.nrows as usize {
            return;
        }

        let starts = asheet.chunk_starts.clone();
        let nrows = asheet.nrows as usize;
        let mut delta = 0isize;
        for col in &mut asheet.columns {
            for (chunk_idx, ch) in col.chunks.iter_mut().enumerate() {
                let Some(&chunk_start) = starts.get(chunk_idx) else {
                    continue;
                };
                let chunk_end = starts
                    .get(chunk_idx + 1)
                    .copied()
                    .unwrap_or(nrows)
                    .min(chunk_start.saturating_add(ch.len()));
                if chunk_end <= start_row0 {
                    continue;
                }
                if chunk_start >= start_row0 {
                    delta = delta.saturating_sub(ch.computed_overlay.clear() as isize);
                } else {
                    let start_in_chunk = start_row0.saturating_sub(chunk_start).min(ch.len());
                    delta = delta
                        .saturating_add(ch.computed_overlay.remove_range(start_in_chunk..ch.len()));
                }
            }

            for (chunk_idx, ch) in &mut col.sparse_chunks {
                let Some(&chunk_start) = starts.get(*chunk_idx) else {
                    continue;
                };
                let chunk_end = starts
                    .get(*chunk_idx + 1)
                    .copied()
                    .unwrap_or(nrows)
                    .min(chunk_start.saturating_add(ch.len()));
                if chunk_end <= start_row0 {
                    continue;
                }
                if chunk_start >= start_row0 {
                    delta = delta.saturating_sub(ch.computed_overlay.clear() as isize);
                } else {
                    let start_in_chunk = start_row0.saturating_sub(chunk_start).min(ch.len());
                    delta = delta
                        .saturating_add(ch.computed_overlay.remove_range(start_in_chunk..ch.len()));
                }
            }
        }
        self.adjust_computed_overlay_bytes(delta);
    }

    fn clear_computed_overlay_after_col(&mut self, sheet: &str, start_col0: usize) {
        if !(self.config.arrow_storage_enabled && self.config.write_formula_overlay_enabled) {
            return;
        }

        let Some(asheet) = self.arrow_sheets.sheet_mut(sheet) else {
            return;
        };
        if start_col0 >= asheet.columns.len() {
            return;
        }

        let mut delta = 0isize;
        for col in asheet.columns.iter_mut().skip(start_col0) {
            for ch in &mut col.chunks {
                delta = delta.saturating_sub(ch.computed_overlay.clear() as isize);
            }
            for ch in col.sparse_chunks.values_mut() {
                delta = delta.saturating_sub(ch.computed_overlay.clear() as isize);
            }
        }
        self.adjust_computed_overlay_bytes(delta);
    }

    #[inline]
    fn literal_to_overlay_value(&self, value: &LiteralValue) -> crate::arrow_store::OverlayValue {
        use crate::arrow_store::OverlayValue;
        match value {
            LiteralValue::Empty => OverlayValue::Empty,
            LiteralValue::Int(i) => OverlayValue::Number(*i as f64),
            LiteralValue::Number(n) => OverlayValue::Number(*n),
            LiteralValue::Boolean(b) => OverlayValue::Boolean(*b),
            LiteralValue::Text(s) => OverlayValue::Text(std::sync::Arc::from(s.clone())),
            LiteralValue::Error(e) => {
                OverlayValue::Error(crate::arrow_store::map_error_code(e.kind))
            }
            LiteralValue::Date(d) => {
                let dt = d.and_hms_opt(0, 0, 0).unwrap();
                let serial =
                    crate::builtins::datetime::datetime_to_serial_for(self.config.date_system, &dt);
                OverlayValue::DateTime(serial)
            }
            LiteralValue::DateTime(dt) => {
                let serial =
                    crate::builtins::datetime::datetime_to_serial_for(self.config.date_system, dt);
                OverlayValue::DateTime(serial)
            }
            LiteralValue::Time(t) => {
                let serial = t.num_seconds_from_midnight() as f64 / 86_400.0;
                OverlayValue::DateTime(serial)
            }
            LiteralValue::Duration(d) => {
                let serial = d.num_seconds() as f64 / 86_400.0;
                OverlayValue::Duration(serial)
            }
            LiteralValue::Pending => OverlayValue::Pending,
            LiteralValue::Array(_) => OverlayValue::Error(crate::arrow_store::map_error_code(
                formualizer_common::ExcelErrorKind::Value,
            )),
        }
    }

    /// Read a single cell's delta overlay entry (if present), preserving the distinction between
    /// absent and explicit `Empty`.
    fn read_delta_overlay_cell(&self, sheet: &str, row: u32, col: u32) -> Option<LiteralValue> {
        if !(self.config.arrow_storage_enabled && self.config.delta_overlay_enabled) {
            return None;
        }
        let asheet = self.arrow_sheets.sheet(sheet)?;
        let row0 = row.saturating_sub(1) as usize;
        let col0 = col.saturating_sub(1) as usize;
        if row0 >= asheet.nrows as usize || col0 >= asheet.columns.len() {
            return None;
        }
        let (ch_idx, in_off) = asheet.chunk_of_row(row0)?;
        let ch = asheet.columns[col0].chunk(ch_idx)?;
        ch.overlay.get_scalar(in_off).map(|ov| ov.to_literal())
    }

    /// Read a single cell's computed overlay entry (if present), preserving the distinction
    /// between absent and explicit `Empty`.
    fn read_computed_overlay_cell(&self, sheet: &str, row: u32, col: u32) -> Option<LiteralValue> {
        if !(self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled)
        {
            return None;
        }
        let asheet = self.arrow_sheets.sheet(sheet)?;
        let row0 = row.saturating_sub(1) as usize;
        let col0 = col.saturating_sub(1) as usize;
        if row0 >= asheet.nrows as usize || col0 >= asheet.columns.len() {
            return None;
        }
        let (ch_idx, in_off) = asheet.chunk_of_row(row0)?;
        let ch = asheet.columns[col0].chunk(ch_idx)?;
        ch.computed_overlay
            .get_scalar(in_off)
            .map(|ov| ov.to_literal())
    }

    fn set_delta_overlay_cell_raw(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        value: Option<LiteralValue>,
    ) {
        if !(self.config.arrow_storage_enabled && self.config.delta_overlay_enabled) {
            return;
        }

        self.ensure_arrow_sheet(sheet);
        let ov_opt = value.as_ref().map(|v| self.literal_to_overlay_value(v));
        let row0 = row.saturating_sub(1) as usize;
        let col0 = col.saturating_sub(1) as usize;
        let asheet = self
            .arrow_sheets
            .sheet_mut(sheet)
            .expect("ArrowSheet must exist");

        let cur_cols = asheet.columns.len();
        if col0 >= cur_cols {
            asheet.insert_columns(cur_cols, (col0 + 1) - cur_cols);
        }
        if row0 >= asheet.nrows as usize {
            if asheet.columns.is_empty() {
                asheet.insert_columns(0, 1);
            }
            asheet.ensure_row_capacity(row0 + 1);
        }

        let Some((ch_idx, in_off)) = asheet.chunk_of_row(row0) else {
            return;
        };
        let Some(ch) = asheet.ensure_column_chunk_mut(col0, ch_idx) else {
            return;
        };

        if let Some(ov) = ov_opt {
            let _ = ch.overlay.set(in_off, ov);
        } else {
            let _ = ch.overlay.remove(in_off);
        }
    }

    fn set_computed_overlay_cell_raw(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        value: Option<LiteralValue>,
    ) {
        if !(self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled)
        {
            return;
        }

        self.ensure_arrow_sheet(sheet);
        let ov_opt = value.as_ref().map(|v| self.literal_to_overlay_value(v));
        let row0 = row.saturating_sub(1) as usize;
        let col0 = col.saturating_sub(1) as usize;
        let asheet = self
            .arrow_sheets
            .sheet_mut(sheet)
            .expect("ArrowSheet must exist");

        let cur_cols = asheet.columns.len();
        if col0 >= cur_cols {
            asheet.insert_columns(cur_cols, (col0 + 1) - cur_cols);
        }
        if row0 >= asheet.nrows as usize {
            if asheet.columns.is_empty() {
                asheet.insert_columns(0, 1);
            }
            asheet.ensure_row_capacity(row0 + 1);
        }

        let Some((ch_idx, in_off)) = asheet.chunk_of_row(row0) else {
            return;
        };
        let Some(ch) = asheet.ensure_column_chunk_mut(col0, ch_idx) else {
            return;
        };

        let delta = if let Some(ov) = ov_opt {
            ch.computed_overlay.set(in_off, ov)
        } else {
            ch.computed_overlay.remove(in_off)
        };
        self.adjust_computed_overlay_bytes(delta);
    }

    fn apply_arrow_undo_batch(&mut self, batch: &crate::engine::ArrowUndoBatch, undo: bool) {
        use crate::engine::ArrowOp;

        let iter: Box<dyn Iterator<Item = &ArrowOp>> = if undo {
            Box::new(batch.ops.iter().rev())
        } else {
            Box::new(batch.ops.iter())
        };

        for op in iter {
            match op {
                ArrowOp::SetDeltaCell {
                    sheet_id,
                    row0,
                    col0,
                    old,
                    new,
                } => {
                    let sheet = self.graph.sheet_name(*sheet_id).to_string();
                    let v = if undo { old.clone() } else { new.clone() };
                    self.set_delta_overlay_cell_raw(&sheet, row0 + 1, col0 + 1, v);
                }
                ArrowOp::SetComputedCell {
                    sheet_id,
                    row0,
                    col0,
                    old,
                    new,
                } => {
                    let sheet = self.graph.sheet_name(*sheet_id).to_string();
                    let v = if undo { old.clone() } else { new.clone() };
                    self.set_computed_overlay_cell_raw(&sheet, row0 + 1, col0 + 1, v);
                }
                ArrowOp::RestoreComputedRect {
                    sheet_id,
                    sr0,
                    sc0,
                    er0,
                    ec0,
                    old,
                    new,
                } => {
                    let sheet = self.graph.sheet_name(*sheet_id).to_string();
                    let vals = if undo { old } else { new };
                    let height = (*er0).saturating_sub(*sr0) as usize + 1;
                    let width = (*ec0).saturating_sub(*sc0) as usize + 1;
                    for r in 0..height {
                        for c in 0..width {
                            let v = vals
                                .get(r)
                                .and_then(|row| row.get(c))
                                .cloned()
                                .unwrap_or(LiteralValue::Empty);
                            self.set_computed_overlay_cell_raw(
                                &sheet,
                                *sr0 + 1 + r as u32,
                                *sc0 + 1 + c as u32,
                                Some(v),
                            );
                        }
                    }
                }
                ArrowOp::InsertRows {
                    sheet_id,
                    before0,
                    count,
                } => {
                    let sheet = self.graph.sheet_name(*sheet_id).to_string();
                    self.ensure_arrow_sheet(&sheet);
                    if let Some(asheet) = self.arrow_sheets.sheet_mut(&sheet) {
                        if undo {
                            asheet.delete_rows(*before0 as usize, *count as usize);
                        } else {
                            asheet.insert_rows(*before0 as usize, *count as usize);
                        }
                    }
                }
                ArrowOp::InsertCols {
                    sheet_id,
                    before0,
                    count,
                } => {
                    let sheet = self.graph.sheet_name(*sheet_id).to_string();
                    self.ensure_arrow_sheet(&sheet);
                    if let Some(asheet) = self.arrow_sheets.sheet_mut(&sheet) {
                        if undo {
                            asheet.delete_columns(*before0 as usize, *count as usize);
                        } else {
                            asheet.insert_columns(*before0 as usize, *count as usize);
                        }
                    }
                }
            }
        }
    }

    fn record_spill_ops_into_arrow_undo(
        &mut self,
        undo: &mut crate::engine::ArrowUndoBatch,
        events: &[crate::engine::ChangeEvent],
    ) {
        use crate::engine::ChangeEvent;
        use formualizer_common::LiteralValue;

        #[allow(clippy::type_complexity)]
        let rect_from_snapshot =
            |snap: &crate::engine::graph::editor::change_log::SpillSnapshot|
             -> Option<(SheetId, u32, u32, u32, u32, Vec<Vec<LiteralValue>>)> {
                if snap.target_cells.is_empty() {
                    return None;
                }
                let sheet_id = snap.target_cells[0].sheet_id;
                let sr0 = snap.target_cells[0].coord.row();
                let sc0 = snap.target_cells[0].coord.col();
                if snap.values.is_empty() || snap.values[0].is_empty() {
                    return None;
                }
                let h = snap.values.len() as u32;
                let w = snap.values[0].len() as u32;
                let er0 = sr0.saturating_add(h.saturating_sub(1));
                let ec0 = sc0.saturating_add(w.saturating_sub(1));
                Some((sheet_id, sr0, sc0, er0, ec0, snap.values.clone()))
            };

        for ev in events {
            match ev {
                ChangeEvent::SpillCommitted { old, new, .. } => {
                    if let Some((sid, sr0, sc0, er0, ec0, new_vals)) = rect_from_snapshot(new) {
                        let old_vals = if let Some(old_snap) = old {
                            rect_from_snapshot(old_snap)
                                .map(|(_, _, _, _, _, v)| v)
                                .unwrap_or_else(|| {
                                    vec![
                                        vec![LiteralValue::Empty; new_vals[0].len()];
                                        new_vals.len()
                                    ]
                                })
                        } else {
                            vec![vec![LiteralValue::Empty; new_vals[0].len()]; new_vals.len()]
                        };
                        undo.record_restore_computed_rect(
                            sid, sr0, sc0, er0, ec0, old_vals, new_vals,
                        );
                    }
                }
                ChangeEvent::SpillCleared { old, .. } => {
                    if let Some((sid, sr0, sc0, er0, ec0, old_vals)) = rect_from_snapshot(old) {
                        let new_vals =
                            vec![vec![LiteralValue::Empty; old_vals[0].len()]; old_vals.len()];
                        undo.record_restore_computed_rect(
                            sid, sr0, sc0, er0, ec0, old_vals, new_vals,
                        );
                    }
                }
                _ => {}
            }
        }
    }

    /// Mirror a value into the computed overlay (formula/spill outputs).
    ///
    /// This path is subject to `EvalConfig.max_overlay_memory_bytes`.
    /// If the cap is exceeded, computed overlays are compacted into base lanes.
    fn mirror_value_to_computed_overlay(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        value: &LiteralValue,
    ) {
        if !(self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled)
        {
            return;
        }
        if self.computed_overlay_mirroring_disabled {
            return;
        }

        let ov = self.literal_to_overlay_value(value);
        self.write_computed_overlay_value_0based(
            sheet,
            row.saturating_sub(1),
            col.saturating_sub(1),
            ov,
        );
    }

    fn write_computed_overlay_value_0based(
        &mut self,
        sheet: &str,
        row0: u32,
        col0: u32,
        value: OverlayValue,
    ) {
        if !(self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled)
        {
            return;
        }
        if self.computed_overlay_mirroring_disabled {
            return;
        }

        self.ensure_arrow_sheet(sheet);

        let row0 = row0 as usize;
        let col0 = col0 as usize;
        let asheet = self
            .arrow_sheets
            .sheet_mut(sheet)
            .expect("ArrowSheet must exist");

        let cur_cols = asheet.columns.len();
        if col0 >= cur_cols {
            asheet.insert_columns(cur_cols, (col0 + 1) - cur_cols);
        }

        if row0 >= asheet.nrows as usize {
            if asheet.columns.is_empty() {
                asheet.insert_columns(0, 1);
            }
            asheet.ensure_row_capacity(row0 + 1);
        }

        let Some((ch_idx, in_off)) = asheet.chunk_of_row(row0) else {
            return;
        };
        let Some(ch) = asheet.ensure_column_chunk_mut(col0, ch_idx) else {
            return;
        };

        let delta = ch.computed_overlay.set_scalar(in_off, value);
        self.adjust_computed_overlay_bytes(delta);

        if let Some(cap) = self.config.max_overlay_memory_bytes
            && self.computed_overlay_bytes_estimate > cap
        {
            self.disable_computed_overlay_mirroring_due_to_budget(cap);
        }
    }

    pub(crate) fn plan_computed_write_coalescing(
        &self,
        buffer: &ComputedWriteBuffer,
    ) -> ComputedWriteCoalescingPlan {
        self.plan_computed_write_coalescing_from_writes(buffer.writes().iter().cloned())
    }

    fn plan_owned_computed_write_coalescing(
        &self,
        writes: Vec<ComputedWrite>,
    ) -> ComputedWriteCoalescingPlan {
        self.plan_computed_write_coalescing_from_writes(writes)
    }

    fn plan_computed_write_coalescing_from_writes(
        &self,
        writes: impl IntoIterator<Item = ComputedWrite>,
    ) -> ComputedWriteCoalescingPlan {
        let mut groups: BTreeMap<ComputedWriteChunkKey, Vec<ComputedWriteChunkEntryPlan>> =
            BTreeMap::new();
        let mut input_cells = 0usize;

        for write in writes {
            match write {
                ComputedWrite::Cell {
                    seq,
                    sheet_id,
                    row0,
                    col0,
                    value,
                } => {
                    input_cells = input_cells.saturating_add(1);
                    self.push_computed_write_plan_entry(
                        &mut groups,
                        seq,
                        sheet_id,
                        row0,
                        col0,
                        value,
                    );
                }
                ComputedWrite::Rect {
                    seq,
                    sheet_id,
                    sr0,
                    sc0,
                    values,
                } => {
                    for (r_off, row) in values.into_iter().enumerate() {
                        for (c_off, value) in row.into_iter().enumerate() {
                            input_cells = input_cells.saturating_add(1);
                            self.push_computed_write_plan_entry(
                                &mut groups,
                                seq,
                                sheet_id,
                                sr0.saturating_add(r_off as u32),
                                sc0.saturating_add(c_off as u32),
                                value,
                            );
                        }
                    }
                }
            }
        }

        let mut plan = ComputedWriteCoalescingPlan {
            chunks: Vec::with_capacity(groups.len()),
            input_cells,
            coalesced_cells: 0,
            overwritten_cells: 0,
        };
        for (key, entries) in groups {
            let (chunk_plan, overwritten) = ComputedWriteChunkPlan::from_group(key, entries);
            plan.coalesced_cells = plan
                .coalesced_cells
                .saturating_add(chunk_plan.entries.len());
            plan.overwritten_cells = plan.overwritten_cells.saturating_add(overwritten);
            plan.chunks.push(chunk_plan);
        }
        debug_assert_eq!(
            plan.input_cells,
            plan.coalesced_cells.saturating_add(plan.overwritten_cells)
        );
        plan
    }

    fn push_computed_write_plan_entry(
        &self,
        groups: &mut BTreeMap<ComputedWriteChunkKey, Vec<ComputedWriteChunkEntryPlan>>,
        seq: u64,
        sheet_id: SheetId,
        row0: u32,
        col0: u32,
        value: OverlayValue,
    ) {
        let (chunk_idx, chunk_start_row0, row_in_chunk) =
            self.locate_computed_write_chunk(sheet_id, row0);
        let key = ComputedWriteChunkKey {
            sheet_id,
            col0,
            chunk_idx,
            chunk_start_row0,
        };
        groups
            .entry(key)
            .or_default()
            .push(ComputedWriteChunkEntryPlan {
                row_in_chunk,
                seq,
                value,
            });
    }

    fn locate_computed_write_chunk(&self, sheet_id: SheetId, row0: u32) -> (usize, u32, usize) {
        let sheet_name = self.graph.sheet_name(sheet_id);
        if let Some(sheet) = self.arrow_sheets.sheet(sheet_name) {
            return Self::locate_row_in_sheet_for_computed_write_plan(sheet, row0 as usize);
        }
        Self::locate_row_in_empty_sheet_for_computed_write_plan(row0 as usize, 32 * 1024)
    }

    fn locate_row_in_sheet_for_computed_write_plan(
        sheet: &crate::arrow_store::ArrowSheet,
        row0: usize,
    ) -> (usize, u32, usize) {
        if row0 < sheet.nrows as usize
            && let Some((chunk_idx, row_in_chunk)) = sheet.chunk_of_row(row0)
        {
            let chunk_start = sheet.chunk_starts.get(chunk_idx).copied().unwrap_or(0);
            return (chunk_idx, chunk_start as u32, row_in_chunk);
        }

        let chunk_rows = sheet.chunk_rows.max(1);
        if sheet.chunk_starts.is_empty() {
            return Self::locate_row_in_empty_sheet_for_computed_write_plan(row0, chunk_rows);
        }

        let mut chunk_idx = sheet.chunk_starts.len().saturating_sub(1);
        let mut chunk_start = sheet.chunk_starts[chunk_idx];
        while chunk_start.saturating_add(chunk_rows) <= row0 {
            chunk_idx = chunk_idx.saturating_add(1);
            chunk_start = chunk_start.saturating_add(chunk_rows);
        }
        (
            chunk_idx,
            chunk_start as u32,
            row0.saturating_sub(chunk_start),
        )
    }

    fn locate_row_in_empty_sheet_for_computed_write_plan(
        row0: usize,
        chunk_rows: usize,
    ) -> (usize, u32, usize) {
        let chunk_rows = chunk_rows.max(1);
        let chunk_idx = row0 / chunk_rows;
        let chunk_start = chunk_idx.saturating_mul(chunk_rows);
        (
            chunk_idx,
            chunk_start as u32,
            row0.saturating_sub(chunk_start),
        )
    }

    #[cfg(test)]
    pub(crate) fn debug_plan_computed_write_coalescing(
        &self,
        buffer: &ComputedWriteBuffer,
    ) -> ComputedWriteCoalescingPlan {
        self.plan_computed_write_coalescing(buffer)
    }

    pub(crate) fn flush_computed_write_buffer(
        &mut self,
        buffer: &mut ComputedWriteBuffer,
    ) -> Result<(), ExcelError> {
        if buffer.is_empty() {
            return Ok(());
        }

        let plan = self.plan_owned_computed_write_coalescing(buffer.take_writes());
        self.flush_computed_write_plan(plan);

        Ok(())
    }

    fn flush_computed_write_plan(&mut self, plan: ComputedWriteCoalescingPlan) {
        for chunk in plan.chunks {
            self.flush_computed_write_chunk_plan(chunk);
        }
    }

    fn flush_computed_write_chunk_plan(&mut self, chunk: ComputedWriteChunkPlan) {
        match &chunk.shape {
            ComputedWriteChunkPlanShape::Point => {
                self.flush_computed_write_chunk_plan_as_points(chunk);
            }
            ComputedWriteChunkPlanShape::SparseOffsets { .. } => {
                self.flush_computed_write_chunk_plan_as_sparse_fragment_or_points(chunk);
            }
            ComputedWriteChunkPlanShape::DenseRange { .. } => {
                self.flush_computed_write_chunk_plan_as_dense_fragment(chunk);
            }
            ComputedWriteChunkPlanShape::RunRange { len, runs, .. } => {
                if Self::should_emit_computed_run_fragment(*len, *runs) {
                    self.flush_computed_write_chunk_plan_as_run_fragment(chunk);
                } else {
                    self.flush_computed_write_chunk_plan_as_dense_fragment(chunk);
                }
            }
        }
    }

    #[inline]
    fn should_emit_computed_run_fragment(len: usize, runs: usize) -> bool {
        runs <= len / 2
    }

    fn flush_computed_write_chunk_plan_as_points(&mut self, chunk: ComputedWriteChunkPlan) {
        let sheet_name = self.graph.sheet_name(chunk.sheet_id).to_string();
        for entry in chunk.entries {
            let row0 = chunk
                .chunk_start_row0
                .saturating_add(entry.row_in_chunk as u32);
            self.write_computed_overlay_value_0based(&sheet_name, row0, chunk.col0, entry.value);
        }
    }

    fn flush_computed_write_chunk_plan_as_sparse_fragment_or_points(
        &mut self,
        chunk: ComputedWriteChunkPlan,
    ) {
        let point_estimate = Self::computed_write_chunk_plan_point_estimate(&chunk);
        let sheet_id = chunk.sheet_id;
        let col0 = chunk.col0;
        let chunk_idx = chunk.chunk_idx;
        let chunk_start_row0 = chunk.chunk_start_row0;
        let items: Vec<(usize, OverlayValue)> = chunk
            .entries
            .into_iter()
            .map(|entry| (entry.row_in_chunk, entry.value))
            .collect();
        match OverlayFragment::sparse_offsets_if_estimated_smaller_than_points(
            items,
            point_estimate,
        ) {
            Some(Ok(fragment)) => {
                self.apply_computed_overlay_fragment(sheet_id, col0, chunk_idx, fragment);
            }
            Some(Err(cells)) => {
                self.flush_computed_overlay_cells_as_points(
                    sheet_id,
                    col0,
                    chunk_start_row0,
                    cells,
                );
            }
            None => {}
        }
    }

    #[inline]
    fn computed_write_chunk_plan_point_estimate(chunk: &ComputedWriteChunkPlan) -> usize {
        chunk
            .entries
            .iter()
            .map(|entry| ComputedWriteBuffer::estimate_value_bytes(&entry.value))
            .fold(0usize, usize::saturating_add)
    }

    fn flush_computed_overlay_cells_as_points(
        &mut self,
        sheet_id: SheetId,
        col0: u32,
        chunk_start_row0: u32,
        cells: Vec<(usize, OverlayValue)>,
    ) {
        let sheet_name = self.graph.sheet_name(sheet_id).to_string();
        for (row_in_chunk, value) in cells {
            let row0 = chunk_start_row0.saturating_add(row_in_chunk as u32);
            self.write_computed_overlay_value_0based(&sheet_name, row0, col0, value);
        }
    }

    fn flush_computed_write_chunk_plan_as_dense_fragment(&mut self, chunk: ComputedWriteChunkPlan) {
        if chunk.entries.is_empty() {
            return;
        }
        let start = chunk.entries[0].row_in_chunk;
        let values: Vec<OverlayValue> =
            chunk.entries.into_iter().map(|entry| entry.value).collect();
        if let Some(fragment) = OverlayFragment::dense_range(start, values) {
            self.apply_computed_overlay_fragment(
                chunk.sheet_id,
                chunk.col0,
                chunk.chunk_idx,
                fragment,
            );
        }
    }

    fn flush_computed_write_chunk_plan_as_run_fragment(&mut self, chunk: ComputedWriteChunkPlan) {
        if chunk.entries.is_empty() {
            return;
        }
        let start = chunk.entries[0].row_in_chunk;
        let values: Vec<OverlayValue> =
            chunk.entries.into_iter().map(|entry| entry.value).collect();
        if let Some(fragment) = OverlayFragment::run_range(start, values) {
            self.apply_computed_overlay_fragment(
                chunk.sheet_id,
                chunk.col0,
                chunk.chunk_idx,
                fragment,
            );
        }
    }

    fn apply_computed_overlay_fragment(
        &mut self,
        sheet_id: SheetId,
        col0: u32,
        chunk_idx: usize,
        fragment: OverlayFragment,
    ) {
        if !(self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled)
        {
            return;
        }
        if self.computed_overlay_mirroring_disabled {
            return;
        }

        let sheet_name = self.graph.sheet_name(sheet_id).to_string();
        self.ensure_arrow_sheet(&sheet_name);

        let col0 = col0 as usize;
        let asheet = self
            .arrow_sheets
            .sheet_mut(&sheet_name)
            .expect("ArrowSheet must exist");

        let cur_cols = asheet.columns.len();
        if col0 >= cur_cols {
            asheet.insert_columns(cur_cols, (col0 + 1) - cur_cols);
        }

        let start_row0 = asheet
            .chunk_starts
            .get(chunk_idx)
            .copied()
            .unwrap_or_else(|| chunk_idx.saturating_mul(asheet.chunk_rows.max(1)));
        let required_rows =
            start_row0.saturating_add(fragment.max_covered_offset().saturating_add(1));
        if required_rows > asheet.nrows as usize {
            if asheet.columns.is_empty() {
                asheet.insert_columns(0, 1);
            }
            asheet.ensure_row_capacity(required_rows);
        }

        let Some(ch) = asheet.ensure_column_chunk_mut(col0, chunk_idx) else {
            return;
        };
        let delta = ch.computed_overlay.apply_fragment(fragment);
        self.adjust_computed_overlay_bytes(delta);

        if let Some(cap) = self.config.max_overlay_memory_bytes
            && self.computed_overlay_bytes_estimate > cap
        {
            self.disable_computed_overlay_mirroring_due_to_budget(cap);
        }
    }

    #[inline]
    fn adjust_computed_overlay_bytes(&mut self, delta: isize) {
        if delta >= 0 {
            self.computed_overlay_bytes_estimate = self
                .computed_overlay_bytes_estimate
                .saturating_add(delta as usize);
        } else {
            self.computed_overlay_bytes_estimate = self
                .computed_overlay_bytes_estimate
                .saturating_sub((-delta) as usize);
        }
    }

    fn clear_all_computed_overlays(&mut self) {
        let mut freed_total = 0usize;
        for sh in self.arrow_sheets.sheets.iter_mut() {
            for col in sh.columns.iter_mut() {
                for ch in col.chunks.iter_mut() {
                    freed_total = freed_total.saturating_add(ch.computed_overlay.clear());
                }
                for ch in col.sparse_chunks.values_mut() {
                    freed_total = freed_total.saturating_add(ch.computed_overlay.clear());
                }
            }
        }
        self.computed_overlay_bytes_estimate = self
            .computed_overlay_bytes_estimate
            .saturating_sub(freed_total);
    }

    fn disable_computed_overlay_mirroring_due_to_budget(&mut self, _cap: usize) {
        // Phase 1 (ticket 610): Arrow-truth is the only supported mode.
        // Handle budget pressure by compacting computed overlays into base lanes.
        self.compact_all_computed_overlays();
    }

    /// Fold all computed overlay entries across all sheets into their base arrays.
    /// This preserves data while freeing overlay memory, allowing mirroring to continue.
    fn compact_all_computed_overlays(&mut self) {
        let mut freed_total = 0usize;
        for sheet in self.arrow_sheets.sheets.iter_mut() {
            for col_idx in 0..sheet.columns.len() {
                // Dense chunks
                let num_dense = sheet.columns[col_idx].chunks.len();
                for ch_idx in 0..num_dense {
                    freed_total += sheet.compact_computed_overlay_chunk(col_idx, ch_idx);
                }
                // Sparse chunks
                let sparse_keys: Vec<usize> = sheet.columns[col_idx]
                    .sparse_chunks
                    .keys()
                    .copied()
                    .collect();
                for ch_idx in sparse_keys {
                    freed_total += sheet.compact_computed_overlay_sparse_chunk(col_idx, ch_idx);
                }
            }
        }
        self.computed_overlay_bytes_estimate = self
            .computed_overlay_bytes_estimate
            .saturating_sub(freed_total);
        self.overlay_compactions = self.overlay_compactions.saturating_add(1);
    }

    fn mirror_vertex_value_to_overlay(&mut self, vertex_id: VertexId, value: &LiteralValue) {
        let _ = self.record_vertex_value_to_overlay(vertex_id, value, None);
    }

    fn record_vertex_value_to_overlay(
        &mut self,
        vertex_id: VertexId,
        value: &LiteralValue,
        computed_writes: Option<&mut ComputedWriteBuffer>,
    ) -> Result<(), ExcelError> {
        if !(self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled)
        {
            return Ok(());
        }
        if self.computed_overlay_mirroring_disabled {
            return Ok(());
        }
        if !matches!(
            self.graph.get_vertex_kind(vertex_id),
            VertexKind::FormulaScalar | VertexKind::FormulaArray
        ) {
            return Ok(());
        }
        let Some(cell) = self.graph.get_cell_ref(vertex_id) else {
            return Ok(());
        };
        let ov = self.literal_to_overlay_value(value);
        if let Some(buffer) = computed_writes {
            buffer.push_cell(cell.sheet_id, cell.coord.row(), cell.coord.col(), ov);
            if self.should_flush_computed_write_buffer(buffer) {
                self.flush_computed_write_buffer(buffer)?;
            }
        } else {
            let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
            self.write_computed_overlay_value_0based(
                &sheet_name,
                cell.coord.row(),
                cell.coord.col(),
                ov,
            );
        }
        Ok(())
    }

    #[inline]
    fn should_flush_computed_write_buffer(&self, buffer: &ComputedWriteBuffer) -> bool {
        self.config.max_overlay_memory_bytes.is_some_and(|cap| {
            if cap == 0 {
                return false;
            }
            self.computed_overlay_bytes_estimate
                .saturating_add(buffer.estimated_bytes())
                > cap
        })
    }

    /// Estimated memory usage for computed overlays (formula/spill mirroring).
    pub fn overlay_memory_usage(&self) -> usize {
        self.computed_overlay_bytes_estimate
    }

    #[cfg(test)]
    pub(crate) fn debug_overlay_compactions(&self) -> u64 {
        self.overlay_compactions
    }

    #[cfg(test)]
    pub(crate) fn debug_recompute_computed_overlay_bytes(&mut self) -> usize {
        let mut total = 0usize;
        for sheet in &self.arrow_sheets.sheets {
            for column in &sheet.columns {
                for chunk in &column.chunks {
                    total = total.saturating_add(chunk.computed_overlay.estimated_bytes());
                }
                for chunk in column.sparse_chunks.values() {
                    total = total.saturating_add(chunk.computed_overlay.estimated_bytes());
                }
            }
        }
        self.computed_overlay_bytes_estimate = total;
        total
    }

    fn resolve_sheet_locator_for_write(
        &mut self,
        loc: formualizer_common::SheetLocator<'_>,
        current_sheet: &str,
    ) -> Result<SheetId, ExcelError> {
        Ok(match loc {
            formualizer_common::SheetLocator::Id(id) => id,
            formualizer_common::SheetLocator::Name(name) => self.graph.sheet_id_mut(name.as_ref()),
            formualizer_common::SheetLocator::Current => self.graph.sheet_id_mut(current_sheet),
        })
    }

    fn resolve_sheet_locator_for_read(
        &self,
        loc: formualizer_common::SheetLocator<'_>,
        current_sheet: &str,
    ) -> Result<SheetId, ExcelError> {
        match loc {
            formualizer_common::SheetLocator::Id(id) => Ok(id),
            formualizer_common::SheetLocator::Name(name) => self
                .graph
                .sheet_id(name.as_ref())
                .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref)),
            formualizer_common::SheetLocator::Current => self
                .graph
                .sheet_id(current_sheet)
                .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref)),
        }
    }

    /// Set a cell value
    pub fn set_cell_value(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        value: LiteralValue,
    ) -> Result<(), ExcelError> {
        let sheet_id = self.graph.sheet_id_mut(sheet);
        self.demote_span_containing_cell_for_write(
            sheet_id,
            row.saturating_sub(1),
            col.saturating_sub(1),
        )
        .map_err(Self::editor_error_to_excel)?;
        self.graph.set_cell_value(sheet, row, col, value.clone())?;
        self.record_formula_plane_changed_cell(sheet, row, col);
        // Mirror into Arrow overlay when enabled
        self.mirror_value_to_overlay(sheet, row, col, &value);
        // Advance snapshot to reflect external mutation
        self.snapshot_id
            .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
        self.has_edited = true;
        Ok(())
    }

    /// Record a single-cell change in FormulaPlane authority so the next
    /// `evaluate_all` under `AuthoritativeExperimental` can derive bounded
    /// span work from `FormulaConsumerReadIndex` instead of recomputing every
    /// active span.
    fn record_formula_plane_changed_cell(&mut self, sheet: &str, row: u32, col: u32) {
        if self.config.formula_plane_mode == FormulaPlaneMode::Off {
            return;
        }
        let sheet_id = self.graph.sheet_id_mut(sheet);
        self.record_formula_plane_structural_change(StructuralScope::Cell {
            sheet: sheet_id,
            row: row.saturating_sub(1),
            col: col.saturating_sub(1),
        });
    }

    fn record_formula_plane_change_for_event(&mut self, event: &ChangeEvent) {
        if self.config.formula_plane_mode == FormulaPlaneMode::Off {
            return;
        }

        match event {
            ChangeEvent::SetValue { addr, .. } | ChangeEvent::SetFormula { addr, .. } => {
                self.record_formula_plane_structural_change(StructuralScope::Cell {
                    sheet: addr.sheet_id,
                    row: addr.coord.row(),
                    col: addr.coord.col(),
                });
            }
            ChangeEvent::SpillCommitted { new, .. } => {
                if let Some(scope) = Self::formula_plane_region_from_cells(&new.target_cells) {
                    self.record_formula_plane_structural_change(scope);
                }
            }
            ChangeEvent::SpillCleared { old, .. } => {
                if let Some(scope) = Self::formula_plane_region_from_cells(&old.target_cells) {
                    self.record_formula_plane_structural_change(scope);
                }
            }
            ChangeEvent::DefineName { .. }
            | ChangeEvent::UpdateName { .. }
            | ChangeEvent::DeleteName { .. }
            | ChangeEvent::VertexMoved { .. }
            | ChangeEvent::FormulaAdjusted { .. }
            | ChangeEvent::NamedRangeAdjusted { .. } => {
                self.record_formula_plane_structural_change(StructuralScope::AllSheets);
            }
            ChangeEvent::SetRowVisibility { sheet_id, row0, .. } => {
                self.record_formula_plane_structural_change(StructuralScope::Region(
                    Region::whole_row(*sheet_id, *row0),
                ));
            }
            ChangeEvent::AddVertex { .. }
            | ChangeEvent::RemoveVertex { .. }
            | ChangeEvent::EdgeAdded { .. }
            | ChangeEvent::EdgeRemoved { .. }
            | ChangeEvent::CompoundStart { .. }
            | ChangeEvent::CompoundEnd { .. }
            | ChangeEvent::StagedFormulaCellChanged { .. } => {}
        }
    }

    fn record_formula_plane_structural_change(&mut self, scope: StructuralScope) {
        if self.config.formula_plane_mode == FormulaPlaneMode::Off {
            return;
        }

        match scope {
            StructuralScope::Cell { sheet, row, col } => {
                self.graph
                    .formula_authority_mut()
                    .record_changed_region(Region::point(sheet, row, col));
            }
            StructuralScope::Region(region) => {
                self.graph
                    .formula_authority_mut()
                    .record_changed_region(region);
            }
            StructuralScope::Sheet(sheet_id) => {
                self.graph
                    .formula_authority_mut()
                    .record_changed_region(Region::whole_sheet(sheet_id));
            }
            StructuralScope::RemovedSheet(sheet_id) => {
                let removed_refs = {
                    let authority = self.graph.formula_authority();
                    authority
                        .active_span_refs()
                        .into_iter()
                        .filter(|span_ref| {
                            authority
                                .plane
                                .spans
                                .get(*span_ref)
                                .map(|span| span.sheet_id == sheet_id)
                                .unwrap_or(false)
                        })
                        .collect::<Vec<_>>()
                };

                let authority = self.graph.formula_authority_mut();
                for span_ref in removed_refs {
                    authority.plane.remove_span(span_ref);
                }
                authority.mark_all_active_spans_dirty();
                let _ = authority.rebuild_indexes();
            }
            StructuralScope::AllSheets => {
                let authority = self.graph.formula_authority_mut();
                authority.mark_all_active_spans_dirty();
                let _ = authority.rebuild_indexes();
            }
        }
    }

    fn formula_plane_region_from_cells(cells: &[CellRef]) -> Option<StructuralScope> {
        let first = cells.first()?;
        let sheet_id = first.sheet_id;
        if cells.iter().any(|cell| cell.sheet_id != sheet_id) {
            return Some(StructuralScope::AllSheets);
        }
        let mut row_start = first.coord.row();
        let mut row_end = row_start;
        let mut col_start = first.coord.col();
        let mut col_end = col_start;
        for cell in cells.iter().skip(1) {
            row_start = row_start.min(cell.coord.row());
            row_end = row_end.max(cell.coord.row());
            col_start = col_start.min(cell.coord.col());
            col_end = col_end.max(cell.coord.col());
        }
        Some(StructuralScope::Region(Region::rect(
            sheet_id, row_start, row_end, col_start, col_end,
        )))
    }

    pub fn set_cell_value_ref(
        &mut self,
        cell: formualizer_common::SheetCellRef<'_>,
        current_sheet: &str,
        value: LiteralValue,
    ) -> Result<(), ExcelError> {
        let owned = cell.into_owned();
        let sheet_id = self.resolve_sheet_locator_for_write(owned.sheet, current_sheet)?;
        let sheet_name = self.graph.sheet_name(sheet_id).to_string();
        self.set_cell_value(
            &sheet_name,
            owned.coord.row() + 1,
            owned.coord.col() + 1,
            value,
        )
    }

    pub fn set_cell_formula_ref(
        &mut self,
        cell: formualizer_common::SheetCellRef<'_>,
        current_sheet: &str,
        ast: ASTNode,
    ) -> Result<(), ExcelError> {
        let owned = cell.into_owned();
        let sheet_id = self.resolve_sheet_locator_for_write(owned.sheet, current_sheet)?;
        let sheet_name = self.graph.sheet_name(sheet_id).to_string();
        self.set_cell_formula(
            &sheet_name,
            owned.coord.row() + 1,
            owned.coord.col() + 1,
            ast,
        )
    }

    pub fn get_cell_value_ref(
        &self,
        cell: formualizer_common::SheetCellRef<'_>,
        current_sheet: &str,
    ) -> Result<Option<LiteralValue>, ExcelError> {
        let owned = cell.into_owned();
        let sheet_id = self.resolve_sheet_locator_for_read(owned.sheet, current_sheet)?;
        let sheet_name = self.graph.sheet_name(sheet_id);
        Ok(self.get_cell_value(sheet_name, owned.coord.row() + 1, owned.coord.col() + 1))
    }

    pub fn resolve_range_view_sheet_ref<'c>(
        &'c self,
        r: &formualizer_common::SheetRef<'_>,
        current_sheet: &str,
    ) -> Result<RangeView<'c>, ExcelError> {
        use formualizer_common::SheetLocator;

        let sheet_to_opt_name = |loc: SheetLocator<'_>| -> Result<Option<String>, ExcelError> {
            match loc {
                SheetLocator::Current => Ok(None),
                SheetLocator::Name(name) => Ok(Some(name.as_ref().to_string())),
                SheetLocator::Id(id) => Ok(Some(self.graph.sheet_name(id).to_string())),
            }
        };

        let rt = match r {
            formualizer_common::SheetRef::Cell(cell) => ReferenceType::Cell {
                sheet: sheet_to_opt_name(cell.sheet.clone())?,
                row: cell.coord.row() + 1,
                col: cell.coord.col() + 1,
                row_abs: cell.coord.row_abs(),
                col_abs: cell.coord.col_abs(),
            },
            formualizer_common::SheetRef::Range(range) => ReferenceType::Range {
                sheet: sheet_to_opt_name(range.sheet.clone())?,
                start_row: range.start_row.map(|b| b.index + 1),
                start_col: range.start_col.map(|b| b.index + 1),
                end_row: range.end_row.map(|b| b.index + 1),
                end_col: range.end_col.map(|b| b.index + 1),
                start_row_abs: range.start_row.map(|b| b.abs).unwrap_or(false),
                start_col_abs: range.start_col.map(|b| b.abs).unwrap_or(false),
                end_row_abs: range.end_row.map(|b| b.abs).unwrap_or(false),
                end_col_abs: range.end_col.map(|b| b.abs).unwrap_or(false),
            },
        };

        crate::traits::EvaluationContext::resolve_range_view(self, &rt, current_sheet)
    }

    /// Set a cell formula
    pub fn set_cell_formula(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
        ast: ASTNode,
    ) -> Result<(), ExcelError> {
        let sheet_id = self.graph.sheet_id_mut(sheet);
        self.demote_span_containing_cell_for_write(
            sheet_id,
            row.saturating_sub(1),
            col.saturating_sub(1),
        )
        .map_err(Self::editor_error_to_excel)?;
        let placement = CellRef::new(sheet_id, Coord::from_excel(row, col, true, true));
        let ingested = {
            let mut pipeline = self.ingest_pipeline();
            pipeline.ingest_formula(FormulaAstInput::Tree(ast), placement, None)?
        };
        self.graph.set_cell_formula_with_plan(
            sheet,
            row,
            col,
            ingested.ast_id,
            &ingested.dep_plan,
            ingested.dep_plan.volatile,
            ingested.dep_plan.dynamic,
        )?;
        self.record_formula_plane_changed_cell(sheet, row, col);

        // If the cell previously held a user value in the delta overlay, it must not continue
        // to mask the formula result under Arrow-canonical reads (overlay precedence is
        // delta -> computed -> base). Remove the overlay entry instead of writing `Empty`,
        // because an explicit `Empty` overlay would still take precedence over computed values.
        self.clear_delta_overlay_cell(sheet, row, col);

        // Advance snapshot to reflect external mutation
        self.mark_topology_edited();
        Ok(())
    }

    /// Bulk set many formulas on a sheet. Skips per-cell snapshot bumping and minimizes edge rebuilds.
    pub fn bulk_set_formulas<I>(&mut self, sheet: &str, items: I) -> Result<usize, ExcelError>
    where
        I: IntoIterator<Item = (u32, u32, ASTNode)>,
    {
        let collected: Vec<(u32, u32, ASTNode)> = items.into_iter().collect();
        let edited_cells: Vec<(u32, u32)> = collected.iter().map(|(r, c, _)| (*r, *c)).collect();
        let sheet_id = self.graph.sheet_id_mut(sheet);
        let writes_inside_active_span = edited_cells.iter().any(|(row, col)| {
            let placement =
                PlacementCoord::new(sheet_id, row.saturating_sub(1), col.saturating_sub(1));
            self.graph
                .formula_authority()
                .plane
                .spans
                .find_at(placement)
                .is_some()
        });
        if writes_inside_active_span {
            self.demote_spans_preserving_computed_overlays(sheet_id, Region::whole_sheet(sheet_id))
                .map_err(Self::editor_error_to_excel)?;
        }
        let ingested = {
            let mut pipeline = self.ingest_pipeline();
            let inputs = collected.into_iter().map(|(row, col, ast)| {
                let placement = CellRef::new(sheet_id, Coord::from_excel(row, col, true, true));
                (FormulaAstInput::Tree(ast), placement, None)
            });
            pipeline.ingest_batch(inputs)?
        };
        let planned = ingested
            .into_iter()
            .map(|formula| {
                (
                    formula.placement.coord.row() + 1,
                    formula.placement.coord.col() + 1,
                    formula.ast_id,
                    formula.dep_plan,
                )
            })
            .collect();
        let n = self.graph.bulk_set_formulas_with_plans(sheet, planned)?;
        for (row, col) in edited_cells {
            self.record_formula_plane_changed_cell(sheet, row, col);
        }
        // Single topology bump after batch
        if n > 0 {
            self.mark_topology_edited();
        }
        Ok(n)
    }

    #[inline]
    fn normalize_public_cell_read(v: LiteralValue) -> Option<LiteralValue> {
        match v {
            LiteralValue::Empty => None,
            LiteralValue::Int(i) => Some(LiteralValue::Number(i as f64)),
            other => Some(other),
        }
    }

    /// Get a cell value
    pub fn get_cell_value(&self, sheet: &str, row: u32, col: u32) -> Option<LiteralValue> {
        self.read_cell_value(sheet, row, col)
            .and_then(Self::normalize_public_cell_read)
    }

    /// Unified internal read API for a single cell value (Arrow-truth).
    pub(crate) fn read_cell_value(&self, sheet: &str, row: u32, col: u32) -> Option<LiteralValue> {
        let asheet = self.sheet_store().sheet(sheet)?;
        let r0 = row.saturating_sub(1) as usize;
        let c0 = col.saturating_sub(1) as usize;
        let v = asheet.get_cell_value(r0, c0);
        if matches!(v, LiteralValue::Empty) {
            None
        } else {
            Some(v)
        }
    }

    /// Unified internal read API for a range of cell values (Arrow-truth).
    pub(crate) fn read_range_values(
        &self,
        sheet: &str,
        sr: u32,
        sc: u32,
        er: u32,
        ec: u32,
    ) -> RangeView<'_> {
        let Some(asheet) = self.sheet_store().sheet(sheet) else {
            return RangeView::from_owned_rows(Vec::new(), self.config.date_system);
        };
        if er < sr || ec < sc {
            return asheet.range_view(1, 1, 0, 0);
        }
        let sr0 = sr.saturating_sub(1) as usize;
        let sc0 = sc.saturating_sub(1) as usize;
        let er0 = er.saturating_sub(1) as usize;
        let ec0 = ec.saturating_sub(1) as usize;
        asheet.range_view(sr0, sc0, er0, ec0)
    }

    /// Get formula AST (if any) and current stored value for a cell
    pub fn get_cell(
        &self,
        sheet: &str,
        row: u32,
        col: u32,
    ) -> Option<(Option<formualizer_parse::ASTNode>, Option<LiteralValue>)> {
        let v = self.get_cell_value(sheet, row, col);
        let sheet_id = self.graph.sheet_id(sheet)?;
        let coord = Coord::from_excel(row, col, true, true);
        let cell = CellRef::new(sheet_id, coord);
        if let Some(vid) = self.graph.get_vertex_for_cell(&cell) {
            let ast = self.graph.get_formula_id(vid).and_then(|ast_id| {
                self.graph
                    .data_store()
                    .retrieve_ast(ast_id, self.graph.sheet_reg())
            });
            return Some((ast, v));
        }

        let placement =
            crate::formula_plane::runtime::PlacementCoord::new(sheet_id, coord.row(), coord.col());
        let handle = self
            .graph
            .formula_authority()
            .plane
            .resolve_formula_at(placement, None);
        let template_id = match handle.resolution {
            crate::formula_plane::runtime::FormulaResolution::SpanPlacement {
                template_id, ..
            } => Some(template_id),
            crate::formula_plane::runtime::FormulaResolution::Overlay(overlay_ref) => self
                .graph
                .formula_authority()
                .plane
                .formula_overlay
                .get(overlay_ref)
                .and_then(|overlay| match overlay.kind {
                    crate::formula_plane::runtime::FormulaOverlayEntryKind::FormulaOverride(
                        template_id,
                    ) => Some(template_id),
                    _ => None,
                }),
            _ => None,
        };
        let ast = template_id.and_then(|template_id| {
            let ast_id = self
                .graph
                .formula_authority()
                .plane
                .templates
                .get(template_id)?
                .ast_id;
            self.graph
                .data_store()
                .retrieve_ast(ast_id, self.graph.sheet_reg())
        });
        if let Some(ast) = ast {
            Some((Some(ast), v))
        } else if v.is_some() {
            Some((None, v))
        } else {
            None
        }
    }

    /// Begin batch operations - defer CSR rebuilds for better performance
    pub fn begin_batch(&mut self) {
        self.graph.begin_batch();
    }

    /// End batch operations and trigger CSR rebuild
    pub fn end_batch(&mut self) {
        self.graph.end_batch();
    }

    /// Begin a deferred-dirty scope for a multi-edit batch: while active,
    /// every edit's dirty propagation queues its sources instead of running
    /// a full BFS per edit, and the outermost `end_deferred_dirty` flushes
    /// the union with ONE multi-source propagation (O(component) instead of
    /// O(edits × component)). See `DependencyGraph::begin_deferred_dirty`.
    ///
    /// Callers MUST run `end_deferred_dirty` on every exit path, including
    /// error returns; evaluation entry points `debug_assert` no scope leaked.
    pub fn begin_deferred_dirty(&mut self) {
        self.graph.begin_deferred_dirty();
    }

    /// End a deferred-dirty scope, flushing the queued propagation when the
    /// outermost scope closes. See `Engine::begin_deferred_dirty`.
    pub fn end_deferred_dirty(&mut self) {
        let _ = self.graph.end_deferred_dirty();
    }

    /// Total vertices processed by dirty-propagation BFS loops since graph
    /// creation. Perf-shape observability only (cross-crate tests assert
    /// batched edits propagate O(component), not O(edits × component)).
    pub fn dirty_propagation_visits(&self) -> u64 {
        self.graph.dirty_propagation_visits()
    }

    /// Evaluate a single vertex.
    /// This is the core of the sequential evaluation logic for Milestone 3.1.
    #[inline]
    fn record_cell_if_changed(
        delta: &mut DeltaCollector,
        cell: &CellRef,
        old: &LiteralValue,
        new: &LiteralValue,
    ) {
        if old != new {
            delta.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
        }
    }

    pub fn evaluate_vertex(&mut self, vertex_id: VertexId) -> Result<LiteralValue, ExcelError> {
        if self.graph.formula_authority().active_span_count() > 0 {
            let _ = self.evaluate_authoritative_formula_plane_all()?;
        }
        self.evaluate_vertex_impl(vertex_id, None)
    }

    fn evaluate_vertex_impl(
        &mut self,
        vertex_id: VertexId,
        delta: Option<&mut DeltaCollector>,
    ) -> Result<LiteralValue, ExcelError> {
        let mut delta = delta;
        // Check if vertex exists
        if !self.graph.vertex_exists(vertex_id) {
            return Err(ExcelError::new(formualizer_common::ExcelErrorKind::Ref)
                .with_message(format!("Vertex not found: {vertex_id:?}")));
        }

        // Get vertex kind and check if it needs evaluation
        let kind = self.graph.get_vertex_kind(vertex_id);
        let sheet_id = self.graph.get_vertex_sheet_id(vertex_id);

        let ast_id = match kind {
            VertexKind::FormulaScalar | VertexKind::FormulaArray => {
                if let Some(ast_id) = self.graph.get_formula_id(vertex_id) {
                    ast_id
                } else {
                    return Ok(LiteralValue::Number(0.0));
                }
            }
            VertexKind::Empty | VertexKind::Cell => {
                if let Some(cell_ref) = self.graph.get_cell_ref(vertex_id) {
                    let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                    let row = cell_ref.coord.row() + 1;
                    let col = cell_ref.coord.col() + 1;
                    if let Some(v) = self.read_cell_value(sheet_name, row, col) {
                        return Ok(v);
                    }
                }
                return Ok(LiteralValue::Number(0.0));
            }
            VertexKind::NamedScalar => {
                let value = self.evaluate_named_scalar(vertex_id, sheet_id)?;
                return Ok(value);
            }
            VertexKind::NamedArray => {
                let value = self.evaluate_named_array(vertex_id, sheet_id)?;
                return Ok(value);
            }
            VertexKind::InfiniteRange
            | VertexKind::Range
            | VertexKind::External
            | VertexKind::Table => {
                // Not directly evaluatable here.
                return Ok(LiteralValue::Number(0.0));
            }
        };

        // The interpreter uses a reference to the engine as the context.
        let sheet_name = self.graph.sheet_name(sheet_id);
        let cell_ref = self
            .graph
            .get_cell_ref(vertex_id)
            .expect("cell ref for vertex");
        let interpreter = Interpreter::new_with_cell(self, sheet_name, cell_ref);

        let result =
            interpreter.evaluate_arena_ast(ast_id, self.graph.data_store(), self.graph.sheet_reg());

        // If array result, perform spill from the anchor cell
        match result {
            Ok(cv) => {
                let result_literal = cv.into_literal();
                match result_literal {
                    LiteralValue::Array(rows) => {
                        // Update kind to FormulaArray for tracking
                        self.graph
                            .set_kind(vertex_id, crate::engine::vertex::VertexKind::FormulaArray);
                        // Build target cells rectangle starting from anchor
                        let anchor = self
                            .graph
                            .get_cell_ref(vertex_id)
                            .expect("cell ref for vertex");
                        let sheet_id = anchor.sheet_id;
                        let h = rows.len() as u32;
                        let w = rows.first().map(|r| r.len()).unwrap_or(0) as u32;

                        // Hard cap to avoid vertex explosion from huge dynamic arrays.
                        let spill_cells = (h as u64).saturating_mul(w as u64);
                        if spill_cells > self.config.spill.max_spill_cells as u64 {
                            self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
                            let spill_err = ExcelError::new(ExcelErrorKind::Spill)
                                .with_message("SpillTooLarge")
                                .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                                    expected_rows: h,
                                    expected_cols: w,
                                });
                            let spill_val = LiteralValue::Error(spill_err.clone());
                            if let Some(d) = delta.as_deref_mut() {
                                let old = self
                                    .read_cell_value(
                                        self.graph.sheet_name(anchor.sheet_id),
                                        anchor.coord.row() + 1,
                                        anchor.coord.col() + 1,
                                    )
                                    .unwrap_or(LiteralValue::Empty);
                                if old != spill_val {
                                    d.record_cell(
                                        anchor.sheet_id,
                                        anchor.coord.row(),
                                        anchor.coord.col(),
                                    );
                                }
                            }
                            self.graph.update_vertex_value(vertex_id, spill_val.clone());
                            if self.config.arrow_storage_enabled
                                && self.config.delta_overlay_enabled
                                && self.config.write_formula_overlay_enabled
                            {
                                let sheet_name = self.graph.sheet_name(anchor.sheet_id).to_string();
                                self.mirror_value_to_computed_overlay(
                                    &sheet_name,
                                    anchor.coord.row() + 1,
                                    anchor.coord.col() + 1,
                                    &spill_val,
                                );
                            }
                            return Ok(spill_val);
                        }
                        // Bounds check to avoid out-of-range writes (align to AbsCoord capacity)
                        const PACKED_MAX_ROW: u32 = 1_048_575; // 20-bit max
                        const PACKED_MAX_COL: u32 = 16_383; // 14-bit max
                        let end_row = anchor.coord.row().saturating_add(h).saturating_sub(1);
                        let end_col = anchor.coord.col().saturating_add(w).saturating_sub(1);
                        if end_row > PACKED_MAX_ROW || end_col > PACKED_MAX_COL {
                            self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
                            let spill_err = ExcelError::new(ExcelErrorKind::Spill)
                                .with_message("Spill exceeds sheet bounds")
                                .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                                    expected_rows: h,
                                    expected_cols: w,
                                });
                            let spill_val = LiteralValue::Error(spill_err.clone());
                            if let Some(d) = delta.as_deref_mut() {
                                let old = self
                                    .read_cell_value(
                                        self.graph.sheet_name(anchor.sheet_id),
                                        anchor.coord.row() + 1,
                                        anchor.coord.col() + 1,
                                    )
                                    .unwrap_or(LiteralValue::Empty);
                                if old != spill_val {
                                    d.record_cell(
                                        anchor.sheet_id,
                                        anchor.coord.row(),
                                        anchor.coord.col(),
                                    );
                                }
                            }
                            self.graph.update_vertex_value(vertex_id, spill_val.clone());
                            if self.config.arrow_storage_enabled
                                && self.config.delta_overlay_enabled
                                && self.config.write_formula_overlay_enabled
                            {
                                let sheet_name = self.graph.sheet_name(anchor.sheet_id).to_string();
                                self.mirror_value_to_computed_overlay(
                                    &sheet_name,
                                    anchor.coord.row() + 1,
                                    anchor.coord.col() + 1,
                                    &spill_val,
                                );
                            }
                            return Ok(spill_val);
                        }
                        let mut targets = Vec::new();
                        for r in 0..h {
                            for c in 0..w {
                                targets.push(self.graph.make_cell_ref_internal(
                                    sheet_id,
                                    anchor.coord.row() + r,
                                    anchor.coord.col() + c,
                                ));
                            }
                        }

                        // Plan spill via spill manager shim
                        match self.spill_mgr.reserve(
                            vertex_id,
                            anchor,
                            SpillShape { rows: h, cols: w },
                            SpillMeta {
                                epoch: self.recalc_epoch,
                                config: self.config.spill,
                            },
                        ) {
                            Ok(()) => {
                                // Commit: write values to grid
                                // Default conflict policy is Error + FirstWins; reserve() enforces in-flight locks
                                // and plan_spill_region enforces overlap with committed formulas/spills/values.
                                if let Err(e) = self.commit_spill_and_mirror(
                                    vertex_id,
                                    &targets,
                                    rows.clone(),
                                    delta.as_deref_mut(),
                                    None,
                                ) {
                                    // If commit fails, mark as error
                                    self.clear_spill_projection_and_mirror(
                                        vertex_id,
                                        delta.as_deref_mut(),
                                    );
                                    if let Some(d) = delta.as_deref_mut() {
                                        let old = self
                                            .read_cell_value(
                                                self.graph.sheet_name(anchor.sheet_id),
                                                anchor.coord.row() + 1,
                                                anchor.coord.col() + 1,
                                            )
                                            .unwrap_or(LiteralValue::Empty);
                                        let new = LiteralValue::Error(e.clone());
                                        if old != new {
                                            d.record_cell(
                                                anchor.sheet_id,
                                                anchor.coord.row(),
                                                anchor.coord.col(),
                                            );
                                        }
                                    }
                                    let err_val = LiteralValue::Error(e.clone());
                                    self.graph.update_vertex_value(vertex_id, err_val.clone());
                                    if self.config.arrow_storage_enabled
                                        && self.config.delta_overlay_enabled
                                        && self.config.write_formula_overlay_enabled
                                    {
                                        let sheet_name =
                                            self.graph.sheet_name(anchor.sheet_id).to_string();
                                        self.mirror_value_to_computed_overlay(
                                            &sheet_name,
                                            anchor.coord.row() + 1,
                                            anchor.coord.col() + 1,
                                            &err_val,
                                        );
                                    }
                                    return Ok(err_val);
                                }
                                // Anchor shows the top-left value, like Excel
                                let top_left = rows
                                    .first()
                                    .and_then(|r| r.first())
                                    .cloned()
                                    .unwrap_or(LiteralValue::Empty);
                                self.graph.update_vertex_value(vertex_id, top_left.clone());
                                Ok(top_left)
                            }
                            Err(e) => {
                                self.clear_spill_projection_and_mirror(
                                    vertex_id,
                                    delta.as_deref_mut(),
                                );
                                let spill_err = ExcelError::new(ExcelErrorKind::Spill)
                                    .with_message(
                                        e.message.unwrap_or_else(|| "Spill blocked".to_string()),
                                    )
                                    .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                                        expected_rows: h,
                                        expected_cols: w,
                                    });
                                let spill_val = LiteralValue::Error(spill_err.clone());
                                if let Some(d) = delta.as_deref_mut() {
                                    let old = self
                                        .read_cell_value(
                                            self.graph.sheet_name(anchor.sheet_id),
                                            anchor.coord.row() + 1,
                                            anchor.coord.col() + 1,
                                        )
                                        .unwrap_or(LiteralValue::Empty);
                                    if old != spill_val {
                                        d.record_cell(
                                            anchor.sheet_id,
                                            anchor.coord.row(),
                                            anchor.coord.col(),
                                        );
                                    }
                                }
                                self.graph.update_vertex_value(vertex_id, spill_val.clone());
                                if self.config.arrow_storage_enabled
                                    && self.config.delta_overlay_enabled
                                    && self.config.write_formula_overlay_enabled
                                {
                                    let sheet_name =
                                        self.graph.sheet_name(anchor.sheet_id).to_string();
                                    self.mirror_value_to_computed_overlay(
                                        &sheet_name,
                                        anchor.coord.row() + 1,
                                        anchor.coord.col() + 1,
                                        &spill_val,
                                    );
                                }
                                Ok(spill_val)
                            }
                        }
                    }
                    other => {
                        // Scalar result: store value and ensure any previous spill is cleared
                        let spill_cells = self
                            .graph
                            .spill_cells_for_anchor(vertex_id)
                            .map(|cells| cells.to_vec())
                            .unwrap_or_default();
                        if let Some(d) = delta.as_deref_mut()
                            && let Some(anchor) = self.graph.get_cell_ref_for_vertex(vertex_id)
                        {
                            if spill_cells.is_empty() {
                                let old = self
                                    .read_cell_value(
                                        self.graph.sheet_name(anchor.sheet_id),
                                        anchor.coord.row() + 1,
                                        anchor.coord.col() + 1,
                                    )
                                    .unwrap_or(LiteralValue::Empty);
                                if old != other {
                                    d.record_cell(
                                        anchor.sheet_id,
                                        anchor.coord.row(),
                                        anchor.coord.col(),
                                    );
                                }
                            } else {
                                for cell in spill_cells.iter() {
                                    let sheet_name = self.graph.sheet_name(cell.sheet_id);
                                    let old = self
                                        .get_cell_value(
                                            sheet_name,
                                            cell.coord.row() + 1,
                                            cell.coord.col() + 1,
                                        )
                                        .unwrap_or(LiteralValue::Empty);
                                    let new = if cell.sheet_id == anchor.sheet_id
                                        && cell.coord.row() == anchor.coord.row()
                                        && cell.coord.col() == anchor.coord.col()
                                    {
                                        other.clone()
                                    } else {
                                        LiteralValue::Empty
                                    };
                                    Self::record_cell_if_changed(d, cell, &old, &new);
                                }
                            }
                        }
                        self.graph.clear_spill_region(vertex_id);
                        if let Some(scope) = Self::formula_plane_region_from_cells(&spill_cells) {
                            self.record_formula_plane_structural_change(scope);
                        }
                        if self.config.arrow_storage_enabled
                            && self.config.delta_overlay_enabled
                            && self.config.write_formula_overlay_enabled
                        {
                            let empty = LiteralValue::Empty;
                            for cell in spill_cells.iter() {
                                let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                                self.mirror_value_to_computed_overlay(
                                    &sheet_name,
                                    cell.coord.row() + 1,
                                    cell.coord.col() + 1,
                                    &empty,
                                );
                            }
                        }
                        self.graph.update_vertex_value(vertex_id, other.clone());
                        // Optionally mirror into Arrow overlay for Arrow-backed reads
                        if self.config.arrow_storage_enabled
                            && self.config.delta_overlay_enabled
                            && self.config.write_formula_overlay_enabled
                        {
                            let anchor = self
                                .graph
                                .get_cell_ref(vertex_id)
                                .expect("cell ref for vertex");
                            let sheet_name = self.graph.sheet_name(anchor.sheet_id).to_string();
                            self.mirror_value_to_computed_overlay(
                                &sheet_name,
                                anchor.coord.row() + 1,
                                anchor.coord.col() + 1,
                                &other,
                            );
                        }
                        Ok(other)
                    }
                }
            }
            Err(e) => {
                // Runtime Excel error: store as a cell value instead of propagating
                // as an exception so bulk eval paths don't fail the whole pass.
                let spill_cells = self
                    .graph
                    .spill_cells_for_anchor(vertex_id)
                    .map(|cells| cells.to_vec())
                    .unwrap_or_default();
                let err_val = LiteralValue::Error(e.clone());
                if let Some(d) = delta
                    && let Some(anchor) = self.graph.get_cell_ref_for_vertex(vertex_id)
                {
                    if spill_cells.is_empty() {
                        let old = self
                            .read_cell_value(
                                self.graph.sheet_name(anchor.sheet_id),
                                anchor.coord.row() + 1,
                                anchor.coord.col() + 1,
                            )
                            .unwrap_or(LiteralValue::Empty);
                        if old != err_val {
                            d.record_cell(anchor.sheet_id, anchor.coord.row(), anchor.coord.col());
                        }
                    } else {
                        for cell in spill_cells.iter() {
                            let sheet_name = self.graph.sheet_name(cell.sheet_id);
                            let old = self
                                .get_cell_value(
                                    sheet_name,
                                    cell.coord.row() + 1,
                                    cell.coord.col() + 1,
                                )
                                .unwrap_or(LiteralValue::Empty);
                            let new = if cell.sheet_id == anchor.sheet_id
                                && cell.coord.row() == anchor.coord.row()
                                && cell.coord.col() == anchor.coord.col()
                            {
                                err_val.clone()
                            } else {
                                LiteralValue::Empty
                            };
                            Self::record_cell_if_changed(d, cell, &old, &new);
                        }
                    }
                }
                self.graph.clear_spill_region(vertex_id);
                if let Some(scope) = Self::formula_plane_region_from_cells(&spill_cells) {
                    self.record_formula_plane_structural_change(scope);
                }
                if self.config.arrow_storage_enabled
                    && self.config.delta_overlay_enabled
                    && self.config.write_formula_overlay_enabled
                {
                    let empty = LiteralValue::Empty;
                    for cell in spill_cells.iter() {
                        let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                        self.mirror_value_to_computed_overlay(
                            &sheet_name,
                            cell.coord.row() + 1,
                            cell.coord.col() + 1,
                            &empty,
                        );
                    }
                }
                self.graph.update_vertex_value(vertex_id, err_val.clone());
                if self.config.arrow_storage_enabled
                    && self.config.delta_overlay_enabled
                    && self.config.write_formula_overlay_enabled
                {
                    let anchor = self
                        .graph
                        .get_cell_ref(vertex_id)
                        .expect("cell ref for vertex");
                    let sheet_name = self.graph.sheet_name(anchor.sheet_id).to_string();
                    self.mirror_value_to_computed_overlay(
                        &sheet_name,
                        anchor.coord.row() + 1,
                        anchor.coord.col() + 1,
                        &err_val,
                    );
                }
                Ok(err_val)
            }
        }
    }

    fn evaluate_named_scalar(
        &mut self,
        vertex_id: VertexId,
        sheet_id: SheetId,
    ) -> Result<LiteralValue, ExcelError> {
        let named_range = self.graph.named_range_by_vertex(vertex_id).ok_or_else(|| {
            ExcelError::new(ExcelErrorKind::Name)
                .with_message("Named range metadata missing".to_string())
        })?;

        match &named_range.definition {
            NamedDefinition::Cell(cell_ref) => {
                let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                let row = cell_ref.coord.row() + 1;
                let col = cell_ref.coord.col() + 1;

                if let Some(dep_vertex) = self.graph.get_vertex_for_cell(cell_ref)
                    && matches!(
                        self.graph.get_vertex_kind(dep_vertex),
                        VertexKind::FormulaScalar | VertexKind::FormulaArray
                    )
                {
                    // Graph does not cache cell/formula values; ensure the precedent is evaluated.
                    let value = self.evaluate_vertex(dep_vertex)?;
                    self.graph.update_vertex_value(vertex_id, value.clone());
                    Ok(value)
                } else {
                    let value = self
                        .get_cell_value(sheet_name, row, col)
                        .unwrap_or(LiteralValue::Empty);
                    self.graph.update_vertex_value(vertex_id, value.clone());
                    Ok(value)
                }
            }
            NamedDefinition::Literal(v) => {
                let out = v.clone();
                self.graph.update_vertex_value(vertex_id, out.clone());
                Ok(out)
            }
            NamedDefinition::Formula { ast, .. } => {
                let context_sheet = match named_range.scope {
                    NameScope::Sheet(id) => id,
                    NameScope::Workbook => sheet_id,
                };
                let sheet_name = self.graph.sheet_name(context_sheet);
                let cell_ref = self
                    .graph
                    .get_cell_ref(vertex_id)
                    .unwrap_or_else(|| self.graph.make_cell_ref(sheet_name, 0, 0));
                let interpreter = Interpreter::new_with_cell(self, sheet_name, cell_ref);
                match interpreter.evaluate_ast(ast) {
                    Ok(cv) => {
                        let value = cv.into_literal();
                        match value {
                            LiteralValue::Array(_) => {
                                let err = ExcelError::new(ExcelErrorKind::NImpl)
                                    .with_message("Array result in scalar named range".to_string());
                                let err_val = LiteralValue::Error(err.clone());
                                self.graph.update_vertex_value(vertex_id, err_val.clone());
                                Ok(err_val)
                            }
                            other => {
                                self.graph.update_vertex_value(vertex_id, other.clone());
                                Ok(other)
                            }
                        }
                    }
                    Err(err) => {
                        let err_val = LiteralValue::Error(err.clone());
                        self.graph.update_vertex_value(vertex_id, err_val.clone());
                        Ok(err_val)
                    }
                }
            }
            NamedDefinition::Range(_) => Err(ExcelError::new(ExcelErrorKind::Value)
                .with_message("Range-valued name evaluated as scalar".to_string())),
        }
    }

    fn evaluate_named_array(
        &mut self,
        vertex_id: VertexId,
        sheet_id: SheetId,
    ) -> Result<LiteralValue, ExcelError> {
        let named_range = self.graph.named_range_by_vertex(vertex_id).ok_or_else(|| {
            ExcelError::new(ExcelErrorKind::Name)
                .with_message("Named range metadata missing".to_string())
        })?;

        let out = match &named_range.definition {
            NamedDefinition::Range(range_ref) => {
                if range_ref.start.sheet_id != range_ref.end.sheet_id {
                    return Err(ExcelError::new(ExcelErrorKind::Ref)
                        .with_message("Named range cannot span sheets".to_string()));
                }

                let sheet_name = self.graph.sheet_name(range_ref.start.sheet_id);
                let sr0 = range_ref.start.coord.row();
                let sc0 = range_ref.start.coord.col();
                let er0 = range_ref.end.coord.row();
                let ec0 = range_ref.end.coord.col();
                if sr0 > er0 || sc0 > ec0 {
                    return Err(ExcelError::new(ExcelErrorKind::Ref)
                        .with_message("Invalid named range bounds".to_string()));
                }

                let h = (er0 - sr0 + 1) as usize;
                let w = (ec0 - sc0 + 1) as usize;
                let cell_count = (h as u64).saturating_mul(w as u64);
                if cell_count > self.config.spill.max_spill_cells as u64 {
                    return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                        "Named range too large to materialize as an array".to_string(),
                    ));
                }

                let mut rows = Vec::with_capacity(h);
                for r0 in sr0..=er0 {
                    let mut row = Vec::with_capacity(w);
                    for c0 in sc0..=ec0 {
                        let v = self
                            .get_cell_value(sheet_name, r0 + 1, c0 + 1)
                            .unwrap_or(LiteralValue::Empty);
                        row.push(v);
                    }
                    rows.push(row);
                }
                LiteralValue::Array(rows)
            }
            NamedDefinition::Cell(cell_ref) => {
                let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                let row = cell_ref.coord.row() + 1;
                let col = cell_ref.coord.col() + 1;
                let v = self
                    .get_cell_value(sheet_name, row, col)
                    .unwrap_or(LiteralValue::Empty);
                LiteralValue::Array(vec![vec![v]])
            }
            NamedDefinition::Literal(v) => LiteralValue::Array(vec![vec![v.clone()]]),
            NamedDefinition::Formula { ast, .. } => {
                let context_sheet = match named_range.scope {
                    NameScope::Sheet(id) => id,
                    NameScope::Workbook => sheet_id,
                };
                let sheet_name = self.graph.sheet_name(context_sheet);
                let cell_ref = self
                    .graph
                    .get_cell_ref(vertex_id)
                    .unwrap_or_else(|| self.graph.make_cell_ref(sheet_name, 0, 0));
                let interpreter = Interpreter::new_with_cell(self, sheet_name, cell_ref);
                match interpreter.evaluate_ast(ast) {
                    Ok(cv) => {
                        let v = cv.into_literal();
                        match v {
                            LiteralValue::Array(_) => v,
                            other => LiteralValue::Array(vec![vec![other]]),
                        }
                    }
                    Err(err) => LiteralValue::Error(err),
                }
            }
        };

        self.graph.update_vertex_value(vertex_id, out.clone());
        Ok(out)
    }

    /// Evaluate only the necessary precedents for specific target cells (demand-driven)
    pub fn evaluate_until(
        &mut self,
        targets: &[(&str, u32, u32)],
    ) -> Result<EvalResult, ExcelError> {
        #[cfg(feature = "tracing")]
        let _span_eval = tracing::info_span!("evaluate_until", targets = targets.len()).entered();
        let start = crate::instant::FzInstant::now();
        self.begin_evaluation_request();
        // Fold any pending edge deltas once so scheduling/eval reads use the
        // zero-allocation CSR slices (#125 write-cheap / read-flush split).
        self.graph.flush_pending_edge_deltas();
        let _source_cache = self.source_cache_session();
        if self.graph.formula_authority().active_span_count() > 0 {
            return self.evaluate_authoritative_formula_plane_all();
        }

        // Parse target cell addresses
        let mut target_addrs = Vec::new();
        for (sheet, row, col) in targets {
            // For now, assume simple A1-style references on default sheet
            // TODO: Parse complex references with sheets
            let sheet_id = self.graph.sheet_id_mut(sheet);
            let coord = Coord::from_excel(*row, *col, true, true);
            target_addrs.push(CellRef::new(sheet_id, coord));
        }

        // Find vertex IDs for targets
        let mut target_vertex_ids = Vec::new();
        for addr in &target_addrs {
            if let Some(vertex_id) = self.graph.get_vertex_id_for_address(addr) {
                target_vertex_ids.push(*vertex_id);
            }
        }

        if target_vertex_ids.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        // Build demand subgraph with virtual edges for compressed ranges
        #[cfg(feature = "tracing")]
        let _span_sub = tracing::info_span!("demand_subgraph_build").entered();
        let (precedents_to_eval, vdeps) = self.build_demand_subgraph(&target_vertex_ids);
        #[cfg(feature = "tracing")]
        drop(_span_sub);

        if precedents_to_eval.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        // Create schedule for the minimal subgraph, honoring virtual edges
        let scheduler = Scheduler::new(&self.graph);
        #[cfg(feature = "tracing")]
        let _span_sched =
            tracing::info_span!("schedule_build", vertices = precedents_to_eval.len()).entered();
        let schedule = scheduler.create_schedule_with_virtual(&precedents_to_eval, &vdeps)?;
        #[cfg(feature = "tracing")]
        drop(_span_sched);

        // Walk schedule units in condensation order: stamp each cyclic SCC at
        // its position, evaluate layers (parallel when enabled, mirroring
        // evaluate_all).
        let mut cycle_errors = 0;
        let mut computed_vertices = 0;
        for &unit in &schedule.units {
            match unit {
                ScheduleUnit::Cycle(i) => {
                    if self.handle_cycle_unit(schedule.unit_cycle(i), None, None, None)? > 0 {
                        cycle_errors += 1;
                    }
                }
                ScheduleUnit::Layer(i) => {
                    let layer = schedule.unit_layer(i);
                    if self.thread_pool.is_some() && layer.vertices.len() > 1 {
                        computed_vertices += self.evaluate_layer_parallel(layer)?;
                    } else {
                        computed_vertices += self.evaluate_layer_sequential(layer)?;
                    }
                }
            }
        }

        // Clear warmup context at end of evaluation

        // Clear dirty flags for evaluated vertices
        self.graph.clear_dirty_flags(&precedents_to_eval);

        // Re-dirty volatile vertices
        self.redirty_for_next_recalc();

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    fn evaluate_until_with_delta_collector(
        &mut self,
        targets: &[(&str, u32, u32)],
        delta: &mut DeltaCollector,
    ) -> Result<EvalResult, ExcelError> {
        #[cfg(feature = "tracing")]
        let _span_eval =
            tracing::info_span!("evaluate_until_with_delta", targets = targets.len()).entered();
        let start = crate::instant::FzInstant::now();
        self.begin_evaluation_request();
        self.graph.flush_pending_edge_deltas();
        let _source_cache = self.source_cache_session();

        let mut target_addrs = Vec::new();
        for (sheet, row, col) in targets {
            let sheet_id = self.graph.sheet_id_mut(sheet);
            let coord = Coord::from_excel(*row, *col, true, true);
            target_addrs.push(CellRef::new(sheet_id, coord));
        }

        let mut target_vertex_ids = Vec::new();
        for addr in &target_addrs {
            if let Some(vertex_id) = self.graph.get_vertex_id_for_address(addr) {
                target_vertex_ids.push(*vertex_id);
            }
        }

        if target_vertex_ids.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        let (precedents_to_eval, vdeps) = self.build_demand_subgraph(&target_vertex_ids);

        if precedents_to_eval.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        let scheduler = Scheduler::new(&self.graph);
        let schedule = scheduler.create_schedule_with_virtual(&precedents_to_eval, &vdeps)?;

        let mut cycle_errors = 0;
        let mut computed_vertices = 0;
        for &unit in &schedule.units {
            match unit {
                ScheduleUnit::Cycle(i) => {
                    if self.handle_cycle_unit(schedule.unit_cycle(i), Some(delta), None, None)? > 0
                    {
                        cycle_errors += 1;
                    }
                }
                ScheduleUnit::Layer(i) => {
                    let layer = schedule.unit_layer(i);
                    if self.thread_pool.is_some() && layer.vertices.len() > 1 {
                        computed_vertices +=
                            self.evaluate_layer_parallel_with_delta(layer, delta)?;
                    } else {
                        computed_vertices +=
                            self.evaluate_layer_sequential_with_delta(layer, delta)?;
                    }
                }
            }
        }

        self.graph.clear_dirty_flags(&precedents_to_eval);
        self.redirty_for_next_recalc();

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    /// Build a reusable evaluation plan that covers every formula vertex in the workbook.
    pub fn build_recalc_plan(&self) -> Result<RecalcPlan, ExcelError> {
        let mut vertices: Vec<VertexId> = self.graph.vertices_with_formulas().collect();
        vertices.sort_unstable();
        if vertices.is_empty() {
            return Ok(RecalcPlan {
                schedule: crate::engine::Schedule {
                    units: Vec::new(),
                    layers: Vec::new(),
                    cycles: Vec::new(),
                },
                has_dynamic_refs: false,
            });
        }

        let has_dynamic_refs = vertices.iter().copied().any(|v| self.graph.is_dynamic(v));
        let (schedule, _, _) = self.create_evaluation_schedule_uncached(&vertices)?;
        Ok(RecalcPlan {
            schedule,
            has_dynamic_refs,
        })
    }

    /// Evaluate using a previously constructed plan. This avoids rebuilding layer schedules for each run.
    pub fn evaluate_recalc_plan(&mut self, plan: &RecalcPlan) -> Result<EvalResult, ExcelError> {
        self.begin_evaluation_request();
        let _source_cache = self.source_cache_session();
        self.validate_deterministic_mode()?;
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            return self.evaluate_authoritative_formula_plane_all();
        }

        let start = crate::instant::FzInstant::now();
        let dirty_vertices = self.graph.get_evaluation_vertices();
        if dirty_vertices.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        // Dynamic-reference formulas (INDIRECT/OFFSET-class) require per-pass virtual-dep
        // augmentation. Reuse the direct recalc flow to preserve semantic parity.
        if plan.has_dynamic_refs {
            self.virtual_dep_fallback_activations =
                self.virtual_dep_fallback_activations.saturating_add(1);
            return self.evaluate_all();
        }

        let dirty_set: FxHashSet<VertexId> = dirty_vertices.iter().copied().collect();
        let mut computed_vertices = 0;
        let mut cycle_errors = 0;

        for &unit in &plan.schedule.units {
            match unit {
                ScheduleUnit::Cycle(i) => {
                    // Recalc-plan quirk (Static): stamp only the DIRTY members
                    // of the cycle, and count the cycle only when it had any.
                    // Under Runtime the filter means: skip when no member is
                    // dirty, evaluate the whole SCC when any is.
                    let stamped = self.handle_cycle_unit(
                        plan.schedule.unit_cycle(i),
                        None,
                        Some(&dirty_set),
                        None,
                    )?;
                    if stamped > 0 {
                        cycle_errors += 1;
                    }
                }
                ScheduleUnit::Layer(i) => {
                    let work: Vec<VertexId> = plan
                        .schedule
                        .unit_layer(i)
                        .vertices
                        .iter()
                        .copied()
                        .filter(|v| dirty_set.contains(v))
                        .collect();
                    if work.is_empty() {
                        continue;
                    }
                    let temp_layer = crate::engine::scheduler::Layer { vertices: work };
                    if self.thread_pool.is_some() && temp_layer.vertices.len() > 1 {
                        computed_vertices += self.evaluate_layer_parallel(&temp_layer)?;
                    } else {
                        computed_vertices += self.evaluate_layer_sequential(&temp_layer)?;
                    }
                }
            }
        }

        self.graph.clear_dirty_flags(&dirty_vertices);
        self.redirty_for_next_recalc();

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }
    fn evaluate_authoritative_formula_plane_all(&mut self) -> Result<EvalResult, ExcelError> {
        // Fresh per-request cycle counters. Some callers (`evaluate_vertex`,
        // `evaluate_cells*`) reach this coordinator without an entry-point
        // reset; callers that did reset have accumulated nothing in between,
        // so the duplicate reset is harmless. The composed legacy primitive
        // below intentionally does not reset, so `evaluate_legacy_cycle_prepass`
        // counts survive into the final telemetry.
        self.begin_evaluation_request();
        // The FormulaPlane coordinator is now selected by mode for evaluate_all.
        // SingletonUnique formulas intentionally remain legacy graph vertices;
        // when no spans are active, execute through the private legacy primitive
        // rather than the public legacy entry path.
        if self.graph.formula_authority().active_span_count() == 0 {
            #[cfg(test)]
            {
                self.last_formula_plane_span_eval_report = None;
            }
            return self.evaluate_all_legacy_impl();
        }

        // Decide span work seeding strategy: any active span we have not yet
        // evaluated under the current authority indexes generation must run
        // whole; subsequent passes use bounded dirty closures derived from
        // captured changed regions.
        let current_indexes_epoch = self.graph.formula_authority().indexes_epoch();
        let span_seed_mode = if self.formula_plane_indexes_epoch_seen != current_indexes_epoch {
            SpanSeedMode::WholeAll
        } else {
            SpanSeedMode::DirtyClosure
        };
        // Take pending regions out of the authority so subsequent reschedules
        // start from a clean slate after a successful eval pass.
        let pending_changed_regions = self
            .graph
            .formula_authority_mut()
            .take_pending_changed_regions();

        // Steady-state shortcut: in `DirtyClosure` mode span work is derived
        // exclusively from pending changed regions, so with none pending the
        // mixed schedule could only ever contain dirty legacy vertices (e.g.
        // re-dirtied volatiles). Skip the O(all formula vertices)
        // producer/consumer index rebuild and run them through the legacy
        // primitive directly — identical evaluation set, with the legacy
        // path's native cycle/virtual-dep handling.
        if matches!(span_seed_mode, SpanSeedMode::DirtyClosure)
            && pending_changed_regions.is_empty()
        {
            #[cfg(test)]
            {
                self.last_formula_plane_span_eval_report = None;
            }
            return self.evaluate_all_legacy_impl();
        }

        let start = crate::instant::FzInstant::now();
        let mut span_seed_mode = span_seed_mode;
        let mut pending_changed_regions = pending_changed_regions;
        // #CIRC stamps produced by demoting cyclic spans and resolving the
        // residual legacy-only cycle ahead of the mixed schedule (gotcha G8).
        let mut prepass_cycle_errors = 0usize;
        const MAX_CYCLE_DEMOTE_ITERS: usize = 64;
        let mut cycle_demote_iters = 0usize;
        let (schedule, span_refs_by_id, plane_epoch, legacy_vertices) = loop {
            let (schedule, span_refs_by_id, plane_epoch, legacy_vertices) =
                self.build_formula_plane_mixed_schedule(span_seed_mode, &pending_changed_regions)?;

            if schedule.is_authoritative_safe() {
                break (schedule, span_refs_by_id, plane_epoch, legacy_vertices);
            }

            // The demote loop below can only make progress on cycles: it
            // demotes cyclic spans and stamps residual legacy-only cycles.
            // Every other fallback reason (capacity caps, unsupported
            // projections, missing result regions) is a property of the
            // inputs — rebuilding the schedule from identical state
            // reproduces the identical fallback, so iterating would spin
            // `MAX_CYCLE_DEMOTE_ITERS` times doing O(graph) schedule builds
            // per iteration before giving up anyway. Fail over to the legacy
            // primitive immediately instead.
            let has_cycle_fallback = schedule.stats.cycle_count > 0
                || schedule
                    .fallbacks
                    .iter()
                    .any(|fb| fb.reason == MixedScheduleFallbackReason::CycleDetected);
            if !has_cycle_fallback {
                self.formula_plane_capacity_bailouts =
                    self.formula_plane_capacity_bailouts.saturating_add(1);
                #[cfg(test)]
                {
                    self.last_formula_plane_span_eval_report = None;
                }
                return self.evaluate_all_legacy_impl();
            }

            // Gotcha G8 (refs #112): a span whose member cell participates in a
            // statically-cyclic SCC must never be span-evaluated. Cross-cell
            // cycles that route through a span producer are invisible to the
            // legacy Tarjan pass (the span member has no graph vertex) and only
            // surface here, as `CycleDetected` fallbacks in the producer-bounded
            // mixed schedule. Demote the cyclic spans to legacy graph vertices
            // so the cycle members move onto the legacy SCC path, then resolve
            // the now legacy-only cycle ahead of the schedule and rebuild.
            // Spans that do not touch the cycle are left untouched.
            let cyclic_spans = self.collect_cyclic_span_refs(&schedule, &span_refs_by_id);
            if !cyclic_spans.is_empty() {
                self.demote_cyclic_spans(&cyclic_spans)?;
            }

            if self.graph.formula_authority().active_span_count() == 0 {
                // All spans demoted; nothing left for the FP coordinator. The
                // legacy evaluator resolves the (now fully legacy) cycle.
                return self.evaluate_all_legacy_impl();
            }

            // Resolve the residual legacy-only cycle (`handle_cycle_unit`
            // honors Static vs Runtime) before rebuilding so the mixed schedule
            // is cycle-free and the surviving spans still get evaluated.
            prepass_cycle_errors =
                prepass_cycle_errors.saturating_add(self.evaluate_legacy_cycle_prepass()?);

            // Re-seed every surviving span whole after the geometry/dirty
            // changes; the demotion already reset
            // `formula_plane_indexes_epoch_seen` to 0.
            span_seed_mode = SpanSeedMode::WholeAll;
            pending_changed_regions = self
                .graph
                .formula_authority_mut()
                .take_pending_changed_regions();

            cycle_demote_iters += 1;
            if cycle_demote_iters >= MAX_CYCLE_DEMOTE_ITERS {
                // Defensive bound: every iteration either demotes ≥1 span or
                // stamps the legacy cycle, both strictly reducing residual work.
                // If we somehow fail to converge, fall back to pure legacy to
                // stay correct rather than spin.
                return self.evaluate_all_legacy_impl();
            }
        };

        let mut computed_vertices = 0usize;
        #[cfg(test)]
        {
            self.last_formula_plane_span_eval_report = None;
        }
        for layer in schedule.layers {
            let mut buffer = ComputedWriteBuffer::default();
            let mut sink = SpanComputedWriteSink::new(&mut buffer);
            let work_items = layer.work;
            let mut work_index = 0usize;
            while work_index < work_items.len() {
                match work_items[work_index].producer {
                    FormulaProducerId::Span(span_id) => {
                        let span_ref = *span_refs_by_id.get(&span_id).ok_or_else(|| {
                            ExcelError::new(ExcelErrorKind::NImpl)
                                .with_message("FormulaPlane schedule referenced a stale span")
                        })?;
                        let sheet_id = {
                            let authority = self.graph.formula_authority();
                            let span = authority.plane.spans.get(span_ref).ok_or_else(|| {
                                ExcelError::new(ExcelErrorKind::NImpl)
                                    .with_message("FormulaPlane schedule referenced a stale span")
                            })?;
                            span.sheet_id
                        };
                        let current_sheet = self.graph.sheet_name(sheet_id);
                        let authority = self.graph.formula_authority();
                        let evaluator = SpanEvaluator::new(
                            &authority.plane,
                            self,
                            current_sheet,
                            self.graph.data_store(),
                            self.graph.sheet_reg(),
                        );
                        #[cfg(test)]
                        let mut last_group_report = None;
                        while work_index < work_items.len() {
                            let FormulaProducerId::Span(group_span_id) =
                                work_items[work_index].producer
                            else {
                                break;
                            };
                            let group_span_ref =
                                *span_refs_by_id.get(&group_span_id).ok_or_else(|| {
                                    ExcelError::new(ExcelErrorKind::NImpl).with_message(
                                        "FormulaPlane schedule referenced a stale span",
                                    )
                                })?;
                            let group_sheet_id = {
                                let authority = self.graph.formula_authority();
                                let span =
                                    authority.plane.spans.get(group_span_ref).ok_or_else(|| {
                                        ExcelError::new(ExcelErrorKind::NImpl).with_message(
                                            "FormulaPlane schedule referenced a stale span",
                                        )
                                    })?;
                                span.sheet_id
                            };
                            if group_sheet_id != sheet_id {
                                break;
                            }

                            let dirty = producer_dirty_to_span_dirty(
                                work_items[work_index].dirty.clone(),
                                group_span_ref,
                            );
                            let task = SpanEvalTask {
                                span: group_span_ref,
                                dirty,
                                plane_epoch,
                            };
                            let report =
                                evaluator.evaluate_task(&task, &mut sink).map_err(|err| {
                                    ExcelError::new(ExcelErrorKind::NImpl).with_message(format!(
                                        "FormulaPlane span evaluation failed: {err:?}"
                                    ))
                                })?;
                            #[cfg(test)]
                            {
                                last_group_report = Some(report.clone());
                            }
                            computed_vertices = computed_vertices
                                .saturating_add(report.span_eval_placement_count as usize);
                            work_index = work_index.saturating_add(1);
                        }
                        #[cfg(test)]
                        {
                            if let Some(report) = last_group_report {
                                self.last_formula_plane_span_eval_report = Some(report);
                            }
                        }
                    }
                    FormulaProducerId::Legacy(_) => {
                        // Batch the contiguous run of legacy work items into a
                        // synthetic layer and evaluate it through the same
                        // coalesced effects pipeline as the legacy scheduler.
                        // Items in one mixed layer have no edges between them
                        // (same invariant the legacy Kahn layers rely on), so
                        // batching preserves ordering semantics while
                        // amortizing per-write overlay mirroring that makes
                        // one-vertex-at-a-time evaluation ~30x slower.
                        let mut vertices = Vec::new();
                        while work_index < work_items.len() {
                            let FormulaProducerId::Legacy(vertex_id) =
                                work_items[work_index].producer
                            else {
                                break;
                            };
                            vertices.push(vertex_id);
                            work_index = work_index.saturating_add(1);
                        }
                        let legacy_layer = crate::engine::scheduler::Layer { vertices };
                        let evaluated =
                            if self.thread_pool.is_some() && legacy_layer.vertices.len() > 1 {
                                self.evaluate_layer_parallel(&legacy_layer)?
                            } else {
                                self.evaluate_layer_sequential(&legacy_layer)?
                            };
                        computed_vertices = computed_vertices.saturating_add(evaluated);
                    }
                }
            }
            self.flush_computed_write_buffer(&mut buffer)?;
        }

        self.graph.clear_dirty_flags(&legacy_vertices);
        // Drop dirty flags on any newly-scheduled FP runtime cells whose graph
        // vertices weren't in the dirty subset (e.g. recently-introduced span
        // result cells); legacy clear_dirty_flags is safe over the full set.
        self.redirty_for_next_recalc();
        // Mark this indexes-epoch as fully evaluated so subsequent passes can
        // use bounded span dirty closures rather than whole-span work.
        self.formula_plane_indexes_epoch_seen = self.graph.formula_authority().indexes_epoch();
        self.recalc_epoch = self.recalc_epoch.wrapping_add(1);
        Ok(EvalResult {
            computed_vertices,
            cycle_errors: prepass_cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    fn build_formula_plane_mixed_schedule(
        &self,
        span_seed_mode: SpanSeedMode,
        pending_changed_regions: &[Region],
    ) -> Result<FormulaPlaneMixedScheduleBuild, ExcelError> {
        let authority = self.graph.formula_authority();
        let mut producer_results = FormulaProducerResultIndex::default();
        let mut consumer_reads = FormulaConsumerReadIndex::default();
        let mut work = Vec::new();

        // Legacy formula producers participate in the mixed runtime only when
        // they are dirty under graph semantics. Result/read indexes still cover
        // every legacy formula so that span->legacy and legacy->span ordering is
        // visible to the scheduler regardless of dirty status, but only dirty
        // vertices receive scheduled work.
        let dirty_legacy: rustc_hash::FxHashSet<VertexId> =
            self.graph.get_evaluation_vertices().into_iter().collect();

        let span_refs = authority.active_span_refs();
        let span_refs_by_id = span_refs
            .iter()
            .copied()
            .map(|span_ref| (span_ref.id, span_ref))
            .collect::<BTreeMap<_, _>>();
        for span_ref in &span_refs {
            let span = authority.plane.spans.get(*span_ref).ok_or_else(|| {
                ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("FormulaPlane active span ref is stale")
            })?;
            let result_region = Region::from_domain(span.result_region.domain());
            producer_results.insert_producer(FormulaProducerId::Span(span.id), result_region);
            let Some(read_summary_id) = span.read_summary_id else {
                return Err(ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("FormulaPlane active span is missing read summary"));
            };
            let Some(read_summary) = authority.plane.span_read_summaries.get(read_summary_id)
            else {
                return Err(ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("FormulaPlane active span has stale read summary"));
            };
            if read_summary.result_region != result_region {
                return Err(ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("FormulaPlane active span read summary is stale"));
            }
            for dependency in &read_summary.dependencies {
                consumer_reads.insert_read(
                    FormulaProducerId::Span(span.id),
                    dependency.read_region,
                    read_summary.result_region,
                    dependency.projection,
                );
            }
            if matches!(span_seed_mode, SpanSeedMode::WholeAll) {
                work.push(FormulaProducerWork {
                    producer: FormulaProducerId::Span(span.id),
                    dirty: ProducerDirtyDomain::Whole,
                });
            }
        }

        let legacy_vertices = self.graph.formula_vertices();
        let mut scheduled_legacy_vertices = Vec::new();
        for vertex in &legacy_vertices {
            let Some(cell) = self.graph.get_cell_ref_for_vertex(*vertex) else {
                continue;
            };
            let result_region = Region::point(cell.sheet_id, cell.coord.row(), cell.coord.col());
            producer_results.insert_producer(FormulaProducerId::Legacy(*vertex), result_region);
            if dirty_legacy.contains(vertex) {
                scheduled_legacy_vertices.push(*vertex);
                work.push(FormulaProducerWork {
                    producer: FormulaProducerId::Legacy(*vertex),
                    dirty: ProducerDirtyDomain::Whole,
                });
            }
        }

        for vertex in &legacy_vertices {
            let Some(cell) = self.graph.get_cell_ref_for_vertex(*vertex) else {
                continue;
            };
            let result_region = Region::point(cell.sheet_id, cell.coord.row(), cell.coord.col());
            let mut seen = rustc_hash::FxHashSet::default();
            for dep in self.graph.get_dependencies(*vertex) {
                let Some(dep_cell) = self.graph.get_cell_ref_for_vertex(dep) else {
                    continue;
                };
                let read_region = Region::point(
                    dep_cell.sheet_id,
                    dep_cell.coord.row(),
                    dep_cell.coord.col(),
                );
                if seen.insert(read_region) {
                    consumer_reads.insert_read(
                        FormulaProducerId::Legacy(*vertex),
                        read_region,
                        result_region,
                        DirtyProjectionRule::WholeResult,
                    );
                }
            }
            if let Some(ranges) = self.graph.get_range_dependencies(*vertex) {
                for range in ranges {
                    let Some(read_region) = self.shared_range_to_region_pattern(range)? else {
                        continue;
                    };
                    if seen.insert(read_region) {
                        consumer_reads.insert_read(
                            FormulaProducerId::Legacy(*vertex),
                            read_region,
                            result_region,
                            DirtyProjectionRule::WholeResult,
                        );
                    }
                }
            }
        }

        // When span seed mode is DirtyClosure, derive bounded span work from
        // captured changed regions via the consumer-read index. This avoids
        // recomputing every active span on edits that only touch a small
        // number of cells.
        if matches!(span_seed_mode, SpanSeedMode::DirtyClosure)
            && !pending_changed_regions.is_empty()
        {
            use crate::formula_plane::producer::compute_dirty_closure;
            let producer_results_ref = &producer_results;
            let closure = compute_dirty_closure(
                &consumer_reads,
                pending_changed_regions.iter().copied(),
                |producer| producer_results_ref.producer_result_region(producer),
            );
            for fallback_work in closure.work {
                work.push(fallback_work);
            }
            // Any unsupported/conservative fallbacks for spans imply we may have
            // missed work; in that case demote to whole-span for affected spans.
            if !closure.fallbacks.is_empty() {
                let mut already_whole: rustc_hash::FxHashSet<_> = work
                    .iter()
                    .filter_map(|w| match (w.producer, &w.dirty) {
                        (FormulaProducerId::Span(id), ProducerDirtyDomain::Whole) => Some(id),
                        _ => None,
                    })
                    .collect();
                for fb in &closure.fallbacks {
                    if let FormulaProducerId::Span(id) = fb.consumer
                        && already_whole.insert(id)
                    {
                        work.push(FormulaProducerWork {
                            producer: FormulaProducerId::Span(id),
                            dirty: ProducerDirtyDomain::Whole,
                        });
                    }
                }
            }
        }

        let schedule = build_mixed_schedule(work, &producer_results, &consumer_reads);
        Ok((
            schedule,
            span_refs_by_id,
            authority.plane.epoch().0,
            scheduled_legacy_vertices,
        ))
    }
}

/// Strategy for seeding span producer work in the FP mixed runtime.
/// `WholeAll` schedules every active span as `Whole`; `DirtyClosure`
/// computes bounded work from captured changed regions only.
#[derive(Clone, Copy, Debug)]
enum SpanSeedMode {
    WholeAll,
    DirtyClosure,
}

impl<R> Engine<R>
where
    R: EvaluationContext,
{
    fn shared_range_to_region_pattern(
        &self,
        range: &crate::reference::SharedRangeRef<'static>,
    ) -> Result<Option<Region>, ExcelError> {
        use crate::reference::SharedSheetLocator;
        let sheet_id = match range.sheet {
            SharedSheetLocator::Id(id) => id,
            SharedSheetLocator::Current => self.graph.default_sheet_id(),
            SharedSheetLocator::Name(_) => return Ok(None),
        };
        match (
            range.start_row,
            range.end_row,
            range.start_col,
            range.end_col,
        ) {
            (Some(sr), Some(er), Some(sc), Some(ec)) => Ok(Some(Region::rect(
                sheet_id, sr.index, er.index, sc.index, ec.index,
            ))),
            (None, None, Some(sc), Some(ec)) if sc.index == ec.index => {
                Ok(Some(Region::whole_col(sheet_id, sc.index)))
            }
            (Some(sr), Some(er), None, None) if sr.index == er.index => {
                Ok(Some(Region::whole_row(sheet_id, sr.index)))
            }
            _ => Ok(None),
        }
    }

    /// Evaluate all dirty/volatile vertices
    pub fn evaluate_all(&mut self) -> Result<EvalResult, ExcelError> {
        debug_assert!(
            !self.graph.deferred_dirty_active(),
            "deferred-dirty scope leaked into evaluate_all: a begin_deferred_dirty \
             was not balanced by end_deferred_dirty"
        );
        self.lookup_index_cache.reset_counters();
        let _source_cache = self.source_cache_session();
        self.validate_deterministic_mode()?;
        if self.config.defer_graph_building {
            // Build graph for all staged formulas before evaluating
            self.build_graph_all()?;
        }
        self.evaluate_all_coordinator()
    }

    /// Central FormulaPlane-aware coordinator for `evaluate_all`. In
    /// `AuthoritativeExperimental` mode every call enters the FormulaPlane
    /// coordinator; the coordinator itself composes with private legacy
    /// primitives for legacy-only work.
    fn evaluate_all_coordinator(&mut self) -> Result<EvalResult, ExcelError> {
        self.begin_evaluation_request();
        if self.config.formula_plane_mode == FormulaPlaneMode::AuthoritativeExperimental {
            return self.evaluate_authoritative_formula_plane_all();
        }
        self.evaluate_all_legacy_impl()
    }

    /// Walk a schedule's units in condensation order: stamp each cyclic SCC
    /// at its position and evaluate each layer (parallel when enabled).
    ///
    /// Returns `(computed_vertices, cycle_count)` where `cycle_count` is the
    /// number of Cycle units walked (the former `schedule.cycles.len()`).
    fn legacy_pass_run_units(
        &mut self,
        schedule: &crate::engine::scheduler::Schedule,
    ) -> Result<(usize, usize), ExcelError> {
        let mut computed_vertices = 0;
        let mut cycle_count = 0;
        for &unit in &schedule.units {
            match unit {
                ScheduleUnit::Cycle(i) => {
                    if self.handle_cycle_unit(schedule.unit_cycle(i), None, None, None)? > 0 {
                        cycle_count += 1;
                    }
                }
                ScheduleUnit::Layer(i) => {
                    let layer = schedule.unit_layer(i);
                    if self.thread_pool.is_some() && layer.vertices.len() > 1 {
                        computed_vertices += self.evaluate_layer_parallel(layer)?;
                    } else {
                        computed_vertices += self.evaluate_layer_sequential(layer)?;
                    }
                }
            }
        }
        Ok((computed_vertices, cycle_count))
    }

    /// Legacy `evaluate_all` body, reachable from the FormulaPlane coordinator
    /// when no active spans exist or FormulaPlane authority is not in
    /// `AuthoritativeExperimental` mode. This is now an internal primitive; it
    /// must not be invoked directly from public APIs.
    ///
    /// Does NOT call `begin_evaluation_request` (cycle-telemetry reset +
    /// per-recalc clock sample): the FormulaPlane coordinator composes this
    /// primitive *after* `evaluate_legacy_cycle_prepass` may have accumulated
    /// counts (G8 demotion path), and both sub-passes belong to ONE request /
    /// one clock sample; request begin happens at the public entry points /
    /// coordinators instead.
    fn evaluate_all_legacy_impl(&mut self) -> Result<EvalResult, ExcelError> {
        self.reset_virtual_dep_telemetry_if_disabled();
        #[cfg(feature = "tracing")]
        let _span_eval = tracing::info_span!("evaluate_all").entered();
        let start = crate::instant::FzInstant::now();
        let mut computed_vertices = 0;
        let mut cycle_errors = 0;
        let mut replan_iterations = 0;
        const MAX_REPLAN: usize = 5;
        let mut telemetry = self
            .config
            .enable_virtual_dep_telemetry
            .then(|| self.start_virtual_dep_telemetry());

        loop {
            let to_evaluate = self.graph.get_evaluation_vertices();
            if to_evaluate.is_empty() {
                if let Some(t) = telemetry.as_mut()
                    && t.bailout_reason.is_none()
                {
                    t.bailout_reason = Some("no_work");
                }
                break;
            }

            let (schedule, old_vdeps, meta) = self.create_evaluation_schedule(&to_evaluate)?;
            if let Some(t) = telemetry.as_mut() {
                Self::accumulate_schedule_meta(t, &meta);
            }

            let (pass_computed, pass_cycles) = self.legacy_pass_run_units(&schedule)?;
            computed_vertices += pass_computed;
            cycle_errors += pass_cycles;

            // Check if dynamic dependencies changed
            let changed_vertices = self.changed_virtual_dep_vertices(&to_evaluate, &old_vdeps);
            if let Some(t) = telemetry.as_mut() {
                t.changed_vdeps_total += changed_vertices.len();
            }

            self.graph.clear_dirty_flags(&to_evaluate);
            for v in &changed_vertices {
                self.graph.set_dirty(*v, true);
            }

            if changed_vertices.is_empty() {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("converged");
                }
                break;
            }
            if replan_iterations >= MAX_REPLAN {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("max_replan");
                }
                break;
            }

            replan_iterations += 1;
        }

        if let Some(mut t) = telemetry {
            t.replan_iterations = replan_iterations;
            self.last_virtual_dep_telemetry = t;
        }

        // Re-dirty volatile vertices for the next evaluation cycle
        self.redirty_for_next_recalc();

        // Advance recalc epoch after a full evaluation pass finishes
        self.recalc_epoch = self.recalc_epoch.wrapping_add(1);

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    pub fn evaluate_all_with_delta(&mut self) -> Result<(EvalResult, EvalDelta), ExcelError> {
        let mut collector = DeltaCollector::new(DeltaMode::Cells);
        let result = self.evaluate_all_with_delta_collector(&mut collector)?;
        Ok((result, collector.finish()))
    }

    fn evaluate_all_with_delta_collector(
        &mut self,
        delta: &mut DeltaCollector,
    ) -> Result<EvalResult, ExcelError> {
        self.begin_evaluation_request();
        let _source_cache = self.source_cache_session();
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            let _ = delta;
            return self.evaluate_authoritative_formula_plane_all();
        }
        self.reset_virtual_dep_telemetry_if_disabled();
        #[cfg(feature = "tracing")]
        let _span_eval = tracing::info_span!("evaluate_all_with_delta").entered();
        let start = crate::instant::FzInstant::now();
        let mut computed_vertices = 0;
        let mut cycle_errors = 0;

        let mut replan_iterations = 0;
        const MAX_REPLAN: usize = 5;
        let mut telemetry = self
            .config
            .enable_virtual_dep_telemetry
            .then(|| self.start_virtual_dep_telemetry());

        loop {
            let to_evaluate = self.graph.get_evaluation_vertices();
            if to_evaluate.is_empty() {
                if let Some(t) = telemetry.as_mut()
                    && t.bailout_reason.is_none()
                {
                    t.bailout_reason = Some("no_work");
                }
                break;
            }

            let (schedule, old_vdeps, meta) = self.create_evaluation_schedule(&to_evaluate)?;
            if let Some(t) = telemetry.as_mut() {
                Self::accumulate_schedule_meta(t, &meta);
            }

            for &unit in &schedule.units {
                match unit {
                    ScheduleUnit::Cycle(i) => {
                        if self.handle_cycle_unit(
                            schedule.unit_cycle(i),
                            Some(delta),
                            None,
                            None,
                        )? > 0
                        {
                            cycle_errors += 1;
                        }
                    }
                    ScheduleUnit::Layer(i) => {
                        let layer = schedule.unit_layer(i);
                        if self.thread_pool.is_some() && layer.vertices.len() > 1 {
                            computed_vertices +=
                                self.evaluate_layer_parallel_with_delta(layer, delta)?;
                        } else {
                            computed_vertices +=
                                self.evaluate_layer_sequential_with_delta(layer, delta)?;
                        }
                    }
                }
            }

            let changed_vertices = self.changed_virtual_dep_vertices(&to_evaluate, &old_vdeps);
            if let Some(t) = telemetry.as_mut() {
                t.changed_vdeps_total += changed_vertices.len();
            }
            self.graph.clear_dirty_flags(&to_evaluate);
            for v in &changed_vertices {
                self.graph.set_dirty(*v, true);
            }

            if changed_vertices.is_empty() {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("converged");
                }
                break;
            }
            if replan_iterations >= MAX_REPLAN {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("max_replan");
                }
                break;
            }
            replan_iterations += 1;
        }

        if let Some(mut t) = telemetry {
            t.replan_iterations = replan_iterations;
            self.last_virtual_dep_telemetry = t;
        }

        self.redirty_for_next_recalc();
        self.recalc_epoch = self.recalc_epoch.wrapping_add(1);

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    /// Convenience: demand-driven evaluation of a single cell by sheet name and row/col.
    ///
    /// This will evaluate only the minimal set of dirty / volatile precedents required
    /// to bring the target cell up-to-date (as if a user asked for that single value),
    /// rather than scheduling a full workbook recalc. If the cell is already clean and
    /// non-volatile, no vertices will be recomputed.
    ///
    /// Returns the (possibly newly computed) value stored for the cell afterwards.
    /// Empty cells return None. Errors are surfaced via the Result type.
    pub fn evaluate_cell(
        &mut self,
        sheet: &str,
        row: u32,
        col: u32,
    ) -> Result<Option<LiteralValue>, ExcelError> {
        if row == 0 || col == 0 {
            return Err(ExcelError::new(ExcelErrorKind::Ref)
                .with_message("Row and column must be >= 1".to_string()));
        }

        // ``defer_graph_building`` mode stages formulas during bulk load
        // and lazily promotes them into the dependency graph at evaluate
        // time. Per-cell evaluation must drain *all* staged sheets, not
        // just the requested target — a cell's formula can reference
        // any sheet in the workbook, and a cross-sheet ref to a still-
        // staged source would silently evaluate to ``None`` if that
        // source sheet hadn't been promoted yet.
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }

        let result = self.evaluate_cells(&[(sheet, row, col)])?;

        match result.len() {
            0 => Ok(None),
            1 => {
                let v = result.into_iter().next().unwrap();
                Ok(v)
            }
            _ => unreachable!("evaluate_cells returned unexpected length"),
        }
    }

    /// Convenience: demand-driven evaluation of multiple cells; accepts a slice of
    /// (sheet, row, col) triples. The union of required dirty / volatile precedents
    /// is computed once and evaluated, which is typically faster than calling
    /// `evaluate_cell` repeatedly for a related set of targets.
    ///
    /// Returns the resulting values for each requested target in the same order.
    pub fn evaluate_cells(
        &mut self,
        targets: &[(&str, u32, u32)],
    ) -> Result<Vec<Option<LiteralValue>>, ExcelError> {
        debug_assert!(
            !self.graph.deferred_dirty_active(),
            "deferred-dirty scope leaked into evaluate_cells: a begin_deferred_dirty \
             was not balanced by end_deferred_dirty"
        );
        self.validate_deterministic_mode()?;
        if targets.is_empty() {
            return Ok(Vec::new());
        }
        // See ``evaluate_cell`` for why we drain *all* staged sheets in
        // ``defer_graph_building`` mode: cross-sheet refs to still-staged
        // sources would otherwise evaluate to ``None``.
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            let _ = self.evaluate_authoritative_formula_plane_all()?;
        } else {
            self.evaluate_until(targets)?;
        }
        Ok(targets
            .iter()
            .map(|(s, r, c)| self.get_cell_value(s, *r, *c))
            .collect())
    }

    pub fn evaluate_cells_cancellable(
        &mut self,
        targets: &[(&str, u32, u32)],
        cancel_flag: Arc<AtomicBool>,
    ) -> Result<Vec<Option<LiteralValue>>, ExcelError> {
        self.active_cancel_flag = Some(cancel_flag.clone());
        let res = self.evaluate_cells_cancellable_impl(targets, &cancel_flag);
        self.active_cancel_flag = None;
        res
    }

    fn evaluate_cells_cancellable_impl(
        &mut self,
        targets: &[(&str, u32, u32)],
        cancel_flag: &AtomicBool,
    ) -> Result<Vec<Option<LiteralValue>>, ExcelError> {
        self.validate_deterministic_mode()?;
        if targets.is_empty() {
            return Ok(Vec::new());
        }
        // See ``evaluate_cell`` for why we drain *all* staged sheets in
        // ``defer_graph_building`` mode: cross-sheet refs to still-staged
        // sources would otherwise evaluate to ``None``.
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            if cancel_flag.load(Ordering::Relaxed) {
                return Err(ExcelError::new(ExcelErrorKind::Cancelled).with_message(
                    "Evaluation cancelled before FormulaPlane scheduling".to_string(),
                ));
            }
            let _ = self.evaluate_authoritative_formula_plane_all()?;
            return Ok(targets
                .iter()
                .map(|(s, r, c)| self.get_cell_value(s, *r, *c))
                .collect());
        }

        // evaluate_until_cancellable takes &[&str] in A1 notation, but we have (&str, u32, u32)
        // Let's implement evaluate_until_coords_cancellable or similar, or just convert
        let a1_targets: Vec<String> = targets
            .iter()
            .map(|(s, r, c)| {
                format!("{}!{}", s, col_letters_from_1based(*c).unwrap()) + &r.to_string()
            })
            .collect();
        let a1_refs: Vec<&str> = a1_targets.iter().map(|s| s.as_str()).collect();

        self.evaluate_until_cancellable_impl(&a1_refs, cancel_flag)?;

        Ok(targets
            .iter()
            .map(|(s, r, c)| self.get_cell_value(s, *r, *c))
            .collect())
    }

    pub fn evaluate_cells_with_delta(
        &mut self,
        targets: &[(&str, u32, u32)],
    ) -> Result<(Vec<Option<LiteralValue>>, EvalDelta), ExcelError> {
        self.validate_deterministic_mode()?;
        if targets.is_empty() {
            return Ok((Vec::new(), EvalDelta::default()));
        }
        if self.config.defer_graph_building {
            let mut sheets: rustc_hash::FxHashSet<&str> = rustc_hash::FxHashSet::default();
            for (s, _, _) in targets.iter() {
                sheets.insert(*s);
            }
            self.build_graph_for_sheets(sheets.iter().cloned())?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            let _ = self.evaluate_authoritative_formula_plane_all()?;
            let values = targets
                .iter()
                .map(|(s, r, c)| self.get_cell_value(s, *r, *c))
                .collect();
            return Ok((values, EvalDelta::default()));
        }
        let mut collector = DeltaCollector::new(DeltaMode::Cells);
        self.evaluate_until_with_delta_collector(targets, &mut collector)?;
        let values = targets
            .iter()
            .map(|(s, r, c)| self.get_cell_value(s, *r, *c))
            .collect();
        Ok((values, collector.finish()))
    }

    /// Get the evaluation plan for target cells without actually evaluating them
    pub fn get_eval_plan(&self, targets: &[(&str, u32, u32)]) -> Result<EvalPlan, ExcelError> {
        if targets.is_empty() {
            return Ok(EvalPlan {
                total_vertices_to_evaluate: 0,
                layers: Vec::new(),
                cycles_detected: 0,
                dirty_count: 0,
                volatile_count: 0,
                parallel_enabled: self.config.enable_parallel && self.thread_pool.is_some(),
                estimated_parallel_layers: 0,
                target_cells: Vec::new(),
            });
        }
        if self.config.defer_graph_building && self.has_staged_formulas() {
            return Err(ExcelError::new(ExcelErrorKind::Value).with_message(
                "Evaluation plan requested with deferred graph; build first or call evaluate_*",
            ));
        }

        // Convert targets to A1 notation for consistency
        let addresses: Vec<String> = targets
            .iter()
            .map(|(s, r, c)| format!("{}!{}{}", s, Self::col_to_letters(*c), r))
            .collect();

        // Parse target cell addresses
        let mut target_addrs = Vec::new();
        for (sheet, row, col) in targets {
            if let Some(sheet_id) = self.graph.sheet_id(sheet) {
                let coord = Coord::from_excel(*row, *col, true, true);
                target_addrs.push(CellRef::new(sheet_id, coord));
            }
        }

        // Find vertex IDs for targets
        let mut target_vertex_ids = Vec::new();
        for addr in &target_addrs {
            if let Some(vertex_id) = self.graph.get_vertex_id_for_address(addr) {
                target_vertex_ids.push(*vertex_id);
            }
        }

        if target_vertex_ids.is_empty() {
            return Ok(EvalPlan {
                total_vertices_to_evaluate: 0,
                layers: Vec::new(),
                cycles_detected: 0,
                dirty_count: 0,
                volatile_count: 0,
                parallel_enabled: self.config.enable_parallel && self.thread_pool.is_some(),
                estimated_parallel_layers: 0,
                target_cells: addresses,
            });
        }

        // Build demand subgraph with virtual edges (same as evaluate_until)
        let (precedents_to_eval, vdeps) = self.build_demand_subgraph(&target_vertex_ids);

        if precedents_to_eval.is_empty() {
            return Ok(EvalPlan {
                total_vertices_to_evaluate: 0,
                layers: Vec::new(),
                cycles_detected: 0,
                dirty_count: 0,
                volatile_count: 0,
                parallel_enabled: self.config.enable_parallel && self.thread_pool.is_some(),
                estimated_parallel_layers: 0,
                target_cells: addresses,
            });
        }

        // Count dirty and volatile vertices
        let mut dirty_count = 0;
        let mut volatile_count = 0;
        for &vertex_id in &precedents_to_eval {
            if self.graph.is_dirty(vertex_id) {
                dirty_count += 1;
            }
            if self.graph.is_volatile(vertex_id) {
                volatile_count += 1;
            }
        }

        // Create schedule for the minimal subgraph honoring virtual edges
        let scheduler = Scheduler::new(&self.graph);
        let schedule = scheduler.create_schedule_with_virtual(&precedents_to_eval, &vdeps)?;

        // Build layer information
        let mut layers = Vec::new();
        let mut estimated_parallel_layers = 0;
        let parallel_enabled = self.config.enable_parallel && self.thread_pool.is_some();

        for layer in &schedule.layers {
            let parallel_eligible = parallel_enabled && layer.vertices.len() > 1;
            if parallel_eligible {
                estimated_parallel_layers += 1;
            }

            // Get sample cell addresses (up to 5)
            let sample_cells: Vec<String> = layer
                .vertices
                .iter()
                .take(5)
                .filter_map(|&vertex_id| {
                    self.graph
                        .get_cell_ref_for_vertex(vertex_id)
                        .map(|cell_ref| {
                            let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                            format!(
                                "{}!{}{}",
                                sheet_name,
                                Self::col_to_letters(cell_ref.coord.col()),
                                cell_ref.coord.row() + 1
                            )
                        })
                })
                .collect();

            layers.push(LayerInfo {
                vertex_count: layer.vertices.len(),
                parallel_eligible,
                sample_cells,
            });
        }

        Ok(EvalPlan {
            total_vertices_to_evaluate: precedents_to_eval.len(),
            layers,
            cycles_detected: schedule.cycles.len(),
            dirty_count,
            volatile_count,
            parallel_enabled,
            estimated_parallel_layers,
            target_cells: addresses,
        })
    }
    /// Helper to create a schedule, integrating virtual dependencies automatically.
    fn create_evaluation_schedule(
        &mut self,
        to_evaluate: &[VertexId],
    ) -> Result<ScheduleBuildOutput, ExcelError> {
        // Fold pending edge deltas once per schedule build so traversal uses
        // the zero-allocation CSR slices (#125).
        self.graph.flush_pending_edge_deltas();
        if self.can_use_static_schedule_cache(to_evaluate) {
            if let Some(cached) = self.cached_static_schedule.as_ref()
                && cached.topology_epoch == self.topology_epoch
                && cached.candidate_vertices.as_slice() == to_evaluate
            {
                let meta = ScheduleBuildMeta {
                    candidate_vertices: to_evaluate.len(),
                    vdeps_vertices: 0,
                    vdeps_edges: 0,
                    builder_elapsed_ms: 0,
                    used_virtual_schedule: false,
                    schedule_cache_hit: true,
                    schedule_cache_eligible: true,
                };
                return Ok((cached.schedule.clone(), FxHashMap::default(), meta));
            }

            let (schedule, vdeps, mut meta) =
                self.create_evaluation_schedule_uncached(to_evaluate)?;
            meta.schedule_cache_hit = false;
            meta.schedule_cache_eligible = true;
            if vdeps.is_empty() {
                self.cached_static_schedule = Some(CachedScheduleEntry {
                    topology_epoch: self.topology_epoch,
                    candidate_vertices: to_evaluate.to_vec(),
                    schedule: schedule.clone(),
                });
            }
            return Ok((schedule, vdeps, meta));
        }

        let (schedule, vdeps, mut meta) = self.create_evaluation_schedule_uncached(to_evaluate)?;
        meta.schedule_cache_hit = false;
        meta.schedule_cache_eligible = false;
        Ok((schedule, vdeps, meta))
    }

    fn create_evaluation_schedule_uncached(
        &self,
        to_evaluate: &[VertexId],
    ) -> Result<ScheduleBuildOutput, ExcelError> {
        let builder = VirtualDepBuilder::new(self);
        let (vdeps, augmented, builder_elapsed_ms, vdeps_edges) =
            if self.config.enable_virtual_dep_telemetry {
                let build_started = crate::instant::FzInstant::now();
                let (vdeps, augmented) = builder.build(to_evaluate);
                let builder_elapsed_ms = build_started.elapsed().as_millis();
                let vdeps_edges = vdeps.values().map(|deps| deps.len()).sum::<usize>();
                (vdeps, augmented, builder_elapsed_ms, vdeps_edges)
            } else {
                let (vdeps, augmented) = builder.build(to_evaluate);
                (vdeps, augmented, 0, 0)
            };

        let mut final_evaluate = to_evaluate.to_vec();
        if !augmented.is_empty() {
            final_evaluate.extend(augmented);
            final_evaluate.sort_unstable();
            final_evaluate.dedup();
        }

        let use_virtual = !vdeps.is_empty();

        let scheduler = Scheduler::new(&self.graph);
        let schedule = if use_virtual {
            scheduler.create_schedule_with_virtual(&final_evaluate, &vdeps)?
        } else {
            scheduler.create_schedule(&final_evaluate)?
        };

        let meta = ScheduleBuildMeta {
            candidate_vertices: to_evaluate.len(),
            vdeps_vertices: vdeps.len(),
            vdeps_edges,
            builder_elapsed_ms,
            used_virtual_schedule: use_virtual,
            schedule_cache_hit: false,
            schedule_cache_eligible: false,
        };

        Ok((schedule, vdeps, meta))
    }

    fn can_use_static_schedule_cache(&self, to_evaluate: &[VertexId]) -> bool {
        !to_evaluate.is_empty()
            && to_evaluate.iter().copied().all(|v| {
                !self.graph.is_dynamic(v) && self.graph.get_range_dependencies(v).is_none()
            })
    }

    fn start_virtual_dep_telemetry(&self) -> VirtualDepTelemetry {
        VirtualDepTelemetry {
            fallback_mode_activations: self.virtual_dep_fallback_activations,
            ..VirtualDepTelemetry::default()
        }
    }

    fn accumulate_schedule_meta(telemetry: &mut VirtualDepTelemetry, meta: &ScheduleBuildMeta) {
        telemetry.candidate_vertices_total += meta.candidate_vertices;
        telemetry.vdeps_vertices_total += meta.vdeps_vertices;
        telemetry.vdeps_edges_total += meta.vdeps_edges;
        telemetry.builder_elapsed_ms_total += meta.builder_elapsed_ms;
        if meta.schedule_cache_eligible {
            if meta.schedule_cache_hit {
                telemetry.schedule_cache_hits += 1;
                telemetry.reused_schedule_vertices_total += meta.candidate_vertices;
            } else {
                telemetry.schedule_cache_misses += 1;
            }
        }
        if meta.used_virtual_schedule {
            telemetry.schedule_virtual_passes += 1;
        } else {
            telemetry.schedule_static_passes += 1;
        }
    }

    fn changed_virtual_dep_vertices(
        &self,
        to_evaluate: &[VertexId],
        old_vdeps: &FxHashMap<VertexId, Vec<VertexId>>,
    ) -> Vec<VertexId> {
        if !to_evaluate
            .iter()
            .copied()
            .any(|v| self.graph.is_dynamic(v))
        {
            return Vec::new();
        }

        let builder = VirtualDepBuilder::new(self);
        let (new_vdeps, _) = builder.build(to_evaluate);

        let mut candidates = FxHashSet::default();
        candidates.extend(old_vdeps.keys().copied());
        candidates.extend(new_vdeps.keys().copied());

        let mut changed = Vec::new();
        for v in candidates {
            if old_vdeps.get(&v) != new_vdeps.get(&v) {
                changed.push(v);
            }
        }
        changed
    }

    /// Build a demand-driven subgraph for the given targets, including ephemeral edges for
    /// compressed ranges, and returning the set of dirty/volatile precedents and virtual deps.
    fn build_demand_subgraph(
        &self,
        target_vertices: &[VertexId],
    ) -> (
        Vec<VertexId>,
        rustc_hash::FxHashMap<VertexId, Vec<VertexId>>,
    ) {
        #[cfg(feature = "tracing")]
        let _span =
            tracing::info_span!("demand_subgraph", targets = target_vertices.len()).entered();
        use rustc_hash::{FxHashMap, FxHashSet};

        let mut to_evaluate: FxHashSet<VertexId> = FxHashSet::default();
        let mut visited: FxHashSet<VertexId> = FxHashSet::default();
        let mut stack: Vec<VertexId> = Vec::new();
        let mut vdeps: FxHashMap<VertexId, Vec<VertexId>> = FxHashMap::default(); // incoming deps per vertex

        for &t in target_vertices {
            stack.push(t);
        }

        while let Some(v) = stack.pop() {
            if !visited.insert(v) {
                continue;
            }
            if !self.graph.vertex_exists(v) {
                continue;
            }
            // Schedule dirty/volatile formulas. Also schedule pass-through
            // Named*/Range vertices so the scheduler honours the
            // topological position of any formula cells that sit underneath
            // them — without these in `vertex_set` the scheduler skips the
            // edges that route a target through a named-range vertex into
            // its underlying cells, and the underlying cells then end up
            // in the same (or an earlier) layer as the target.
            match self.graph.get_vertex_kind(v) {
                VertexKind::FormulaScalar | VertexKind::FormulaArray => {
                    if self.graph.is_dirty(v) || self.graph.is_volatile(v) {
                        to_evaluate.insert(v);
                    }
                }
                VertexKind::NamedScalar
                | VertexKind::NamedArray
                | VertexKind::Range
                | VertexKind::InfiniteRange => {
                    to_evaluate.insert(v);
                }
                _ => {}
            }

            // Explicit dependencies (graph edges). We push *every* dep onto
            // the stack — not just formulas — because intermediate vertices
            // (NamedScalar, NamedArray, Range) are pass-through nodes whose
            // own dependencies point at the actual formula cells. Filtering
            // by kind here previously caused DN-range refs to be dropped
            // from the demand subgraph, so a target like
            // ``=SUM(named_range_pointing_at_dirty_cells)`` would evaluate
            // using stale values for those cells. The kind check at the top
            // of the loop still gates which vertices end up in
            // ``to_evaluate``; only Formula vertices are scheduled.
            if let Some(dependencies) = self.graph.dependencies_slice(v) {
                for &dep in dependencies {
                    if self.graph.vertex_exists(dep) && !visited.contains(&dep) {
                        stack.push(dep);
                    }
                }
            } else {
                for dep in self.graph.get_dependencies(v) {
                    if self.graph.vertex_exists(dep) && !visited.contains(&dep) {
                        stack.push(dep);
                    }
                }
            } // Virtual dependencies (compressed ranges + dynamic like INDIRECT)
            let builder = VirtualDepBuilder::new(self);
            let (vdeps_map, _) = builder.build(&[v]);
            if let Some(deps) = vdeps_map.get(&v) {
                for &u in deps {
                    vdeps.entry(v).or_default().push(u);
                    if !visited.contains(&u) {
                        stack.push(u);
                    }
                }
            }
        }

        let mut result: Vec<VertexId> = to_evaluate.into_iter().collect();
        result.sort_unstable();
        // Dedup virtual deps
        for deps in vdeps.values_mut() {
            deps.sort_unstable();
            deps.dedup();
        }
        (result, vdeps)
    }

    /// Helper: convert 1-based column index to Excel-style letters (1 -> A, 27 -> AA)
    fn col_to_letters(col: u32) -> String {
        col_letters_from_1based(col).expect("column index must be >= 1")
    }

    /// Evaluate all dirty/volatile vertices with cancellation support
    pub fn evaluate_all_cancellable(
        &mut self,
        cancel_flag: Arc<AtomicBool>,
    ) -> Result<EvalResult, ExcelError> {
        self.active_cancel_flag = Some(cancel_flag.clone());
        let res = self.evaluate_all_cancellable_impl(&cancel_flag);
        self.active_cancel_flag = None;
        res
    }

    fn evaluate_all_cancellable_impl(
        &mut self,
        cancel_flag: &AtomicBool,
    ) -> Result<EvalResult, ExcelError> {
        self.begin_evaluation_request();
        let _source_cache = self.source_cache_session();
        self.validate_deterministic_mode()?;
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            if cancel_flag.load(Ordering::Relaxed) {
                return Err(ExcelError::new(ExcelErrorKind::Cancelled).with_message(
                    "Evaluation cancelled before FormulaPlane scheduling".to_string(),
                ));
            }
            return self.evaluate_authoritative_formula_plane_all();
        }
        self.reset_virtual_dep_telemetry_if_disabled();
        let start = crate::instant::FzInstant::now();
        let mut computed_vertices = 0;
        let mut cycle_errors = 0;

        let mut replan_iterations = 0;
        const MAX_REPLAN: usize = 5;
        let mut telemetry = self
            .config
            .enable_virtual_dep_telemetry
            .then(|| self.start_virtual_dep_telemetry());

        loop {
            if cancel_flag.load(Ordering::Relaxed) {
                if let Some(mut t) = telemetry {
                    t.bailout_reason = Some("cancelled");
                    t.replan_iterations = replan_iterations;
                    self.last_virtual_dep_telemetry = t;
                }
                return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                    .with_message("Evaluation cancelled before scheduling".to_string()));
            }

            let to_evaluate = self.graph.get_evaluation_vertices();
            if to_evaluate.is_empty() {
                if let Some(t) = telemetry.as_mut()
                    && t.bailout_reason.is_none()
                {
                    t.bailout_reason = Some("no_work");
                }
                break;
            }

            let (schedule, old_vdeps, meta) = self.create_evaluation_schedule(&to_evaluate)?;
            if let Some(t) = telemetry.as_mut() {
                Self::accumulate_schedule_meta(t, &meta);
            }

            // Walk units in condensation order, checking cancellation between
            // units (formerly between cycles and between layers).
            for &unit in &schedule.units {
                match unit {
                    ScheduleUnit::Cycle(i) => {
                        // Check cancellation between cycles
                        if cancel_flag.load(Ordering::Relaxed) {
                            if let Some(mut t) = telemetry {
                                t.bailout_reason = Some("cancelled");
                                t.replan_iterations = replan_iterations;
                                self.last_virtual_dep_telemetry = t;
                            }
                            return Err(ExcelError::new(ExcelErrorKind::Cancelled).with_message(
                                "Evaluation cancelled during cycle handling".to_string(),
                            ));
                        }

                        if self.handle_cycle_unit(
                            schedule.unit_cycle(i),
                            None,
                            None,
                            Some(cancel_flag),
                        )? > 0
                        {
                            cycle_errors += 1;
                        }
                    }
                    ScheduleUnit::Layer(i) => {
                        let layer = schedule.unit_layer(i);
                        // Check cancellation between layers
                        if cancel_flag.load(Ordering::Relaxed) {
                            if let Some(mut t) = telemetry {
                                t.bailout_reason = Some("cancelled");
                                t.replan_iterations = replan_iterations;
                                self.last_virtual_dep_telemetry = t;
                            }
                            return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                                .with_message("Evaluation cancelled between layers".to_string()));
                        }

                        // Evaluate vertices in this layer (parallel or sequential)
                        if self.thread_pool.is_some() && layer.vertices.len() > 1 {
                            computed_vertices +=
                                self.evaluate_layer_parallel_cancellable(layer, cancel_flag)?;
                        } else {
                            computed_vertices +=
                                self.evaluate_layer_sequential_cancellable(layer, cancel_flag)?;
                        }
                    }
                }
            }

            let changed_vertices = self.changed_virtual_dep_vertices(&to_evaluate, &old_vdeps);
            if let Some(t) = telemetry.as_mut() {
                t.changed_vdeps_total += changed_vertices.len();
            }
            self.graph.clear_dirty_flags(&to_evaluate);
            for v in &changed_vertices {
                self.graph.set_dirty(*v, true);
            }

            if changed_vertices.is_empty() {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("converged");
                }
                break;
            }
            if replan_iterations >= MAX_REPLAN {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("max_replan");
                }
                break;
            }
            replan_iterations += 1;
        }

        if let Some(mut t) = telemetry {
            t.replan_iterations = replan_iterations;
            self.last_virtual_dep_telemetry = t;
        }

        // Re-dirty volatile vertices for the next evaluation cycle
        self.redirty_for_next_recalc();
        self.recalc_epoch = self.recalc_epoch.wrapping_add(1);

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    /// Evaluate only the necessary precedents for specific target cells with cancellation support
    pub fn evaluate_until_cancellable(
        &mut self,
        targets: &[&str],
        cancel_flag: Arc<AtomicBool>,
    ) -> Result<EvalResult, ExcelError> {
        self.active_cancel_flag = Some(cancel_flag.clone());
        let res = self.evaluate_until_cancellable_impl(targets, &cancel_flag);
        self.active_cancel_flag = None;
        res
    }

    fn evaluate_until_cancellable_impl(
        &mut self,
        targets: &[&str],
        cancel_flag: &AtomicBool,
    ) -> Result<EvalResult, ExcelError> {
        let start = crate::instant::FzInstant::now();
        self.begin_evaluation_request();
        self.graph.flush_pending_edge_deltas();
        if self.graph.formula_authority().active_span_count() > 0 {
            if cancel_flag.load(Ordering::Relaxed) {
                return Err(ExcelError::new(ExcelErrorKind::Cancelled).with_message(
                    "Evaluation cancelled before FormulaPlane scheduling".to_string(),
                ));
            }
            return self.evaluate_authoritative_formula_plane_all();
        }

        // Parse target cell addresses
        let mut target_addrs = Vec::new();
        for target in targets {
            let (sheet, row, col) = self.parse_a1_notation(target)?;
            let sheet_id = self.graph.sheet_id_mut(&sheet);
            let coord = Coord::from_excel(row, col, true, true);
            target_addrs.push(CellRef::new(sheet_id, coord));
        }

        // Find vertex IDs for targets
        let mut target_vertex_ids = Vec::new();
        for addr in &target_addrs {
            if let Some(vertex_id) = self.graph.get_vertex_id_for_address(addr) {
                target_vertex_ids.push(*vertex_id);
            }
        }

        if target_vertex_ids.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        // Build demand subgraph with virtual edges
        let (precedents_to_eval, vdeps) = self.build_demand_subgraph(&target_vertex_ids);

        if precedents_to_eval.is_empty() {
            return Ok(EvalResult {
                computed_vertices: 0,
                cycle_errors: 0,
                elapsed: start.elapsed(),
            });
        }

        // Create schedule honoring virtual edges
        let scheduler = Scheduler::new(&self.graph);
        let schedule = scheduler.create_schedule_with_virtual(&precedents_to_eval, &vdeps)?;

        // Walk units in condensation order with cancellation checks between
        // units (formerly between cycles and between layers).
        let mut cycle_errors = 0;
        let mut computed_vertices = 0;
        for &unit in &schedule.units {
            match unit {
                ScheduleUnit::Cycle(i) => {
                    // Check cancellation between cycles
                    if cancel_flag.load(Ordering::Relaxed) {
                        return Err(ExcelError::new(ExcelErrorKind::Cancelled).with_message(
                            "Demand-driven evaluation cancelled during cycle handling".to_string(),
                        ));
                    }

                    if self.handle_cycle_unit(
                        schedule.unit_cycle(i),
                        None,
                        None,
                        Some(cancel_flag),
                    )? > 0
                    {
                        cycle_errors += 1;
                    }
                }
                ScheduleUnit::Layer(i) => {
                    let layer = schedule.unit_layer(i);
                    // Check cancellation between layers
                    if cancel_flag.load(Ordering::Relaxed) {
                        return Err(ExcelError::new(ExcelErrorKind::Cancelled).with_message(
                            "Demand-driven evaluation cancelled between layers".to_string(),
                        ));
                    }

                    // Evaluate vertices in this layer (parallel or sequential)
                    if self.thread_pool.is_some() && layer.vertices.len() > 1 {
                        computed_vertices +=
                            self.evaluate_layer_parallel_cancellable(layer, cancel_flag)?;
                    } else {
                        computed_vertices += self
                            .evaluate_layer_sequential_cancellable_demand_driven(
                                layer,
                                cancel_flag,
                            )?;
                    }
                }
            }
        }

        // Clear dirty flags for evaluated vertices
        self.graph.clear_dirty_flags(&precedents_to_eval);

        // Re-dirty volatile vertices
        self.redirty_for_next_recalc();

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    fn parse_a1_notation(&self, address: &str) -> Result<(String, u32, u32), ExcelError> {
        let mut parts = address.splitn(2, '!');
        let first = parts.next().unwrap_or_default();
        let remainder = parts.next();

        let (sheet, cell_part) = match remainder {
            Some(cell) => (first.to_string(), cell),
            None => (self.default_sheet_name().to_string(), first),
        };

        let (row, col, _, _) = parse_a1_1based(cell_part).map_err(|err| {
            ExcelError::new(ExcelErrorKind::Ref)
                .with_message(format!("Invalid cell reference `{cell_part}`: {err}"))
        })?;

        Ok((sheet, row, col))
    }

    /// Determine volatility using this engine's FunctionProvider, falling back to global registry.
    fn is_ast_volatile_with_provider(&self, ast: &ASTNode) -> bool {
        use formualizer_parse::parser::ASTNodeType;
        match &ast.node_type {
            ASTNodeType::Function { name, args, .. } => {
                if let Some(func) = self
                    .get_function("", name)
                    .or_else(|| crate::function_registry::get("", name))
                    && func.caps().contains(crate::function::FnCaps::VOLATILE)
                {
                    return true;
                }
                args.iter()
                    .any(|arg| self.is_ast_volatile_with_provider(arg))
            }
            ASTNodeType::BinaryOp { left, right, .. } => {
                self.is_ast_volatile_with_provider(left)
                    || self.is_ast_volatile_with_provider(right)
            }
            ASTNodeType::UnaryOp { expr, .. } => self.is_ast_volatile_with_provider(expr),
            ASTNodeType::Array(rows) => rows.iter().any(|row| {
                row.iter()
                    .any(|cell| self.is_ast_volatile_with_provider(cell))
            }),
            _ => false,
        }
    }

    /// Find dirty precedents that need evaluation for the given target vertices
    fn find_dirty_precedents(&self, target_vertices: &[VertexId]) -> Vec<VertexId> {
        let mut to_evaluate = FxHashSet::default();
        let mut visited = FxHashSet::default();
        let mut stack = Vec::new();

        // Start reverse traversal from target vertices
        for &target in target_vertices {
            stack.push(target);
        }

        while let Some(vertex_id) = stack.pop() {
            if !visited.insert(vertex_id) {
                continue; // Already processed
            }

            if self.graph.vertex_exists(vertex_id) {
                // Check if this vertex needs evaluation
                let kind = self.graph.get_vertex_kind(vertex_id);
                let needs_eval = match kind {
                    super::vertex::VertexKind::FormulaScalar
                    | super::vertex::VertexKind::FormulaArray => {
                        self.graph.is_dirty(vertex_id) || self.graph.is_volatile(vertex_id)
                    }
                    _ => false, // Values and empty cells don't need evaluation
                };

                if needs_eval {
                    to_evaluate.insert(vertex_id);
                }

                // Continue traversal to dependencies (precedents)
                if let Some(dependencies) = self.graph.dependencies_slice(vertex_id) {
                    for &dep_id in dependencies {
                        if !visited.contains(&dep_id) {
                            stack.push(dep_id);
                        }
                    }
                } else {
                    let dependencies = self.graph.get_dependencies(vertex_id);
                    for dep_id in dependencies {
                        if !visited.contains(&dep_id) {
                            stack.push(dep_id);
                        }
                    }
                }
            }
        }

        let mut result: Vec<VertexId> = to_evaluate.into_iter().collect();
        result.sort_unstable();
        result
    }

    /// Evaluate a layer sequentially
    fn evaluate_layer_sequential(
        &mut self,
        layer: &super::scheduler::Layer,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_sequential_effects(layer)
    }

    fn update_vertex_value_with_delta(
        &mut self,
        vertex_id: VertexId,
        new_value: LiteralValue,
        delta: &mut DeltaCollector,
    ) {
        if delta.mode != DeltaMode::Off
            && let Some(cell) = self.graph.get_cell_ref_for_vertex(vertex_id)
        {
            let sheet_name = self.graph.sheet_name(cell.sheet_id);
            let old = self
                .read_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                .unwrap_or(LiteralValue::Empty);
            if old != new_value {
                delta.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
            }
        }
        self.graph.update_vertex_value(vertex_id, new_value.clone());
        self.mirror_vertex_value_to_overlay(vertex_id, &new_value);
    }

    fn evaluate_layer_sequential_with_delta(
        &mut self,
        layer: &super::scheduler::Layer,
        delta: &mut DeltaCollector,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_sequential_with_delta_effects(layer, delta)
    }

    /// Evaluate a layer sequentially with cancellation support
    fn evaluate_layer_sequential_cancellable(
        &mut self,
        layer: &super::scheduler::Layer,
        cancel_flag: &AtomicBool,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_sequential_cancellable_effects(layer, cancel_flag)
    }

    /// Evaluate a layer sequentially with more frequent cancellation checks for demand-driven evaluation
    fn evaluate_layer_sequential_cancellable_demand_driven(
        &mut self,
        layer: &super::scheduler::Layer,
        cancel_flag: &AtomicBool,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_sequential_cancellable_demand_driven_effects(layer, cancel_flag)
    }

    /// Evaluate a layer in parallel using the thread pool
    fn evaluate_layer_parallel(
        &mut self,
        layer: &super::scheduler::Layer,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_parallel_effects(layer)
    }

    fn evaluate_layer_parallel_with_delta(
        &mut self,
        layer: &super::scheduler::Layer,
        delta: &mut DeltaCollector,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_parallel_with_delta_effects(layer, delta)
    }

    /// Evaluate a layer in parallel with cancellation support
    fn evaluate_layer_parallel_cancellable(
        &mut self,
        layer: &super::scheduler::Layer,
        cancel_flag: &AtomicBool,
    ) -> Result<usize, ExcelError> {
        self.evaluate_layer_parallel_cancellable_effects(layer, cancel_flag)
    }

    /// Apply a computed result produced by `evaluate_vertex_immutable()`.
    ///
    /// This is the parallel equivalent of the "apply" portion of `evaluate_vertex_impl`.
    /// We keep apply sequential for correctness (spill commit is inherently stateful).
    fn apply_parallel_vertex_result(
        &mut self,
        vertex_id: VertexId,
        result: LiteralValue,
        mut delta: Option<&mut DeltaCollector>,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
    ) -> Result<(), ExcelError> {
        // If this vertex's cell is currently covered by a spill from a different anchor,
        // ignore the computed result. The spill's committed values own the grid.
        if let Some(cell) = self.graph.get_cell_ref(vertex_id)
            && let Some(owner) = self.graph.spill_registry_anchor_for_cell(cell)
            && owner != vertex_id
        {
            return Ok(());
        }

        let kind = self.graph.get_vertex_kind(vertex_id);

        // Only formula vertices spill dynamic arrays into the grid.
        let is_formula = matches!(kind, VertexKind::FormulaScalar | VertexKind::FormulaArray);
        if is_formula {
            match result {
                LiteralValue::Array(rows) => {
                    self.apply_array_result_from_parallel(
                        vertex_id,
                        rows,
                        delta.as_deref_mut(),
                        overwritable_formulas,
                    )?;
                }
                other => {
                    self.apply_non_array_result_from_parallel(
                        vertex_id,
                        other,
                        delta.as_deref_mut(),
                    );
                }
            }
            return Ok(());
        }

        // Non-formula vertices: store value as-is (arrays remain arrays; no spill).
        if let Some(d) = delta {
            self.update_vertex_value_with_delta(vertex_id, result, d);
        } else {
            self.graph.update_vertex_value(vertex_id, result.clone());
            self.mirror_vertex_value_to_overlay(vertex_id, &result);
        }
        Ok(())
    }

    fn apply_non_array_result_from_parallel(
        &mut self,
        vertex_id: VertexId,
        value: LiteralValue,
        delta: Option<&mut DeltaCollector>,
    ) {
        // Scalar/error result: store value and ensure any previous spill is cleared.
        // This mirrors the sequential behavior in `evaluate_vertex_impl`.
        let spill_cells = self
            .graph
            .spill_cells_for_anchor(vertex_id)
            .map(|cells| cells.to_vec())
            .unwrap_or_default();

        if let Some(d) = delta
            && d.mode != DeltaMode::Off
            && let Some(anchor) = self.graph.get_cell_ref_for_vertex(vertex_id)
        {
            if spill_cells.is_empty() {
                let old = self
                    .read_cell_value(
                        self.graph.sheet_name(anchor.sheet_id),
                        anchor.coord.row() + 1,
                        anchor.coord.col() + 1,
                    )
                    .unwrap_or(LiteralValue::Empty);
                if old != value {
                    d.record_cell(anchor.sheet_id, anchor.coord.row(), anchor.coord.col());
                }
            } else {
                for cell in spill_cells.iter() {
                    let sheet_name = self.graph.sheet_name(cell.sheet_id);
                    let old = self
                        .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                        .unwrap_or(LiteralValue::Empty);
                    let new = if cell.sheet_id == anchor.sheet_id
                        && cell.coord.row() == anchor.coord.row()
                        && cell.coord.col() == anchor.coord.col()
                    {
                        value.clone()
                    } else {
                        LiteralValue::Empty
                    };
                    Self::record_cell_if_changed(d, cell, &old, &new);
                }
            }
        }

        self.graph.clear_spill_region(vertex_id);
        if let Some(scope) = Self::formula_plane_region_from_cells(&spill_cells) {
            self.record_formula_plane_structural_change(scope);
        }

        if self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled
        {
            let empty = LiteralValue::Empty;
            for cell in spill_cells.iter() {
                let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                self.mirror_value_to_computed_overlay(
                    &sheet_name,
                    cell.coord.row() + 1,
                    cell.coord.col() + 1,
                    &empty,
                );
            }
        }

        self.graph.update_vertex_value(vertex_id, value.clone());
        self.mirror_vertex_value_to_overlay(vertex_id, &value);
    }

    fn apply_array_result_from_parallel(
        &mut self,
        vertex_id: VertexId,
        rows: Vec<Vec<LiteralValue>>,
        mut delta: Option<&mut DeltaCollector>,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
    ) -> Result<(), ExcelError> {
        // Keep behavior consistent with the sequential spill path in `evaluate_vertex_impl`.
        self.graph
            .set_kind(vertex_id, crate::engine::vertex::VertexKind::FormulaArray);

        let anchor = self
            .graph
            .get_cell_ref(vertex_id)
            .expect("cell ref for vertex");
        let sheet_id = anchor.sheet_id;
        let h = rows.len() as u32;
        let w = rows.first().map(|r| r.len()).unwrap_or(0) as u32;

        // Hard cap to avoid vertex explosion from huge dynamic arrays.
        let spill_cells = (h as u64).saturating_mul(w as u64);
        if spill_cells > self.config.spill.max_spill_cells as u64 {
            self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
            let spill_err = ExcelError::new(ExcelErrorKind::Spill)
                .with_message("SpillTooLarge")
                .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                    expected_rows: h,
                    expected_cols: w,
                });
            let spill_val = LiteralValue::Error(spill_err.clone());
            if let Some(d) = delta.as_deref_mut()
                && d.mode != DeltaMode::Off
            {
                let old = self
                    .read_cell_value(
                        self.graph.sheet_name(anchor.sheet_id),
                        anchor.coord.row() + 1,
                        anchor.coord.col() + 1,
                    )
                    .unwrap_or(LiteralValue::Empty);
                if old != spill_val {
                    d.record_cell(anchor.sheet_id, anchor.coord.row(), anchor.coord.col());
                }
            }
            self.graph.update_vertex_value(vertex_id, spill_val.clone());
            self.mirror_vertex_value_to_overlay(vertex_id, &spill_val);
            return Ok(());
        }

        // Bounds check to avoid out-of-range writes (align to AbsCoord capacity)
        const PACKED_MAX_ROW: u32 = 1_048_575; // 20-bit max
        const PACKED_MAX_COL: u32 = 16_383; // 14-bit max
        let end_row = anchor.coord.row().saturating_add(h).saturating_sub(1);
        let end_col = anchor.coord.col().saturating_add(w).saturating_sub(1);
        if end_row > PACKED_MAX_ROW || end_col > PACKED_MAX_COL {
            self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
            let spill_err = ExcelError::new(ExcelErrorKind::Spill)
                .with_message("Spill exceeds sheet bounds")
                .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                    expected_rows: h,
                    expected_cols: w,
                });
            let spill_val = LiteralValue::Error(spill_err.clone());
            if let Some(d) = delta.as_deref_mut()
                && d.mode != DeltaMode::Off
            {
                let old = self
                    .read_cell_value(
                        self.graph.sheet_name(anchor.sheet_id),
                        anchor.coord.row() + 1,
                        anchor.coord.col() + 1,
                    )
                    .unwrap_or(LiteralValue::Empty);
                if old != spill_val {
                    d.record_cell(anchor.sheet_id, anchor.coord.row(), anchor.coord.col());
                }
            }
            self.graph.update_vertex_value(vertex_id, spill_val.clone());
            self.mirror_vertex_value_to_overlay(vertex_id, &spill_val);
            return Ok(());
        }

        let mut targets = Vec::new();
        for r in 0..h {
            for c in 0..w {
                targets.push(self.graph.make_cell_ref_internal(
                    sheet_id,
                    anchor.coord.row() + r,
                    anchor.coord.col() + c,
                ));
            }
        }

        match self.spill_mgr.reserve(
            vertex_id,
            anchor,
            SpillShape { rows: h, cols: w },
            SpillMeta {
                epoch: self.recalc_epoch,
                config: self.config.spill,
            },
        ) {
            Ok(()) => {
                if let Err(e) = self.commit_spill_and_mirror(
                    vertex_id,
                    &targets,
                    rows.clone(),
                    delta.as_deref_mut(),
                    overwritable_formulas,
                ) {
                    self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
                    let err_val = LiteralValue::Error(e.clone());
                    if let Some(d) = delta.as_deref_mut()
                        && d.mode != DeltaMode::Off
                    {
                        let old = self
                            .read_cell_value(
                                self.graph.sheet_name(anchor.sheet_id),
                                anchor.coord.row() + 1,
                                anchor.coord.col() + 1,
                            )
                            .unwrap_or(LiteralValue::Empty);
                        if old != err_val {
                            d.record_cell(anchor.sheet_id, anchor.coord.row(), anchor.coord.col());
                        }
                    }
                    self.graph.update_vertex_value(vertex_id, err_val.clone());
                    self.mirror_vertex_value_to_overlay(vertex_id, &err_val);
                    return Ok(());
                }

                // Anchor shows the top-left value, like Excel
                let top_left = rows
                    .first()
                    .and_then(|r| r.first())
                    .cloned()
                    .unwrap_or(LiteralValue::Empty);
                self.graph.update_vertex_value(vertex_id, top_left.clone());
                self.mirror_vertex_value_to_overlay(vertex_id, &top_left);
                Ok(())
            }
            Err(e) => {
                self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
                let spill_err = ExcelError::new(ExcelErrorKind::Spill)
                    .with_message(e.message.unwrap_or_else(|| "Spill blocked".to_string()))
                    .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                        expected_rows: h,
                        expected_cols: w,
                    });
                let spill_val = LiteralValue::Error(spill_err.clone());
                if let Some(d) = delta
                    && d.mode != DeltaMode::Off
                {
                    let old = self
                        .read_cell_value(
                            self.graph.sheet_name(anchor.sheet_id),
                            anchor.coord.row() + 1,
                            anchor.coord.col() + 1,
                        )
                        .unwrap_or(LiteralValue::Empty);
                    if old != spill_val {
                        d.record_cell(anchor.sheet_id, anchor.coord.row(), anchor.coord.col());
                    }
                }
                self.graph.update_vertex_value(vertex_id, spill_val.clone());
                self.mirror_vertex_value_to_overlay(vertex_id, &spill_val);
                Ok(())
            }
        }
    }

    /// Evaluate a single vertex without mutating the graph (for parallel evaluation)
    fn evaluate_vertex_immutable(&self, vertex_id: VertexId) -> Result<LiteralValue, ExcelError> {
        // Check if vertex exists
        if !self.graph.vertex_exists(vertex_id) {
            return Err(ExcelError::new(formualizer_common::ExcelErrorKind::Ref)
                .with_message(format!("Vertex not found: {vertex_id:?}")));
        }

        // Get vertex kind and check if it needs evaluation
        let kind = self.graph.get_vertex_kind(vertex_id);
        let sheet_id = self.graph.get_vertex_sheet_id(vertex_id);

        let ast_id = match kind {
            VertexKind::FormulaScalar | VertexKind::FormulaArray => {
                if let Some(ast_id) = self.graph.get_formula_id(vertex_id) {
                    ast_id
                } else {
                    return Ok(LiteralValue::Number(0.0));
                }
            }
            VertexKind::Empty | VertexKind::Cell => {
                if let Some(cell_ref) = self.graph.get_cell_ref(vertex_id) {
                    let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                    let row = cell_ref.coord.row() + 1;
                    let col = cell_ref.coord.col() + 1;
                    if let Some(v) = self.read_cell_value(sheet_name, row, col) {
                        return Ok(v);
                    }
                }
                return Ok(LiteralValue::Number(0.0));
            }
            VertexKind::NamedScalar => {
                let named_range = self.graph.named_range_by_vertex(vertex_id).ok_or_else(|| {
                    ExcelError::new(ExcelErrorKind::Name)
                        .with_message("Named range metadata missing".to_string())
                })?;

                return match &named_range.definition {
                    NamedDefinition::Cell(cell_ref) => {
                        let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                        Ok(self
                            .get_cell_value(
                                sheet_name,
                                cell_ref.coord.row() + 1,
                                cell_ref.coord.col() + 1,
                            )
                            .unwrap_or(LiteralValue::Empty))
                    }
                    NamedDefinition::Literal(v) => Ok(v.clone()),
                    NamedDefinition::Formula { ast, .. } => {
                        let context_sheet = match named_range.scope {
                            NameScope::Sheet(id) => id,
                            NameScope::Workbook => sheet_id,
                        };
                        let sheet_name = self.graph.sheet_name(context_sheet);
                        let cell_ref = self
                            .graph
                            .get_cell_ref(vertex_id)
                            .unwrap_or_else(|| self.graph.make_cell_ref(sheet_name, 0, 0));
                        let interpreter = Interpreter::new_with_cell(self, sheet_name, cell_ref);
                        interpreter.evaluate_ast(ast).map(|cv| cv.into_literal())
                    }
                    NamedDefinition::Range(_) => Err(ExcelError::new(ExcelErrorKind::Value)
                        .with_message("Range-valued name evaluated as scalar".to_string())),
                };
            }
            VertexKind::NamedArray => {
                let named_range = self.graph.named_range_by_vertex(vertex_id).ok_or_else(|| {
                    ExcelError::new(ExcelErrorKind::Name)
                        .with_message("Named range metadata missing".to_string())
                })?;

                return match &named_range.definition {
                    NamedDefinition::Range(range_ref) => {
                        if range_ref.start.sheet_id != range_ref.end.sheet_id {
                            return Err(ExcelError::new(ExcelErrorKind::Ref)
                                .with_message("Named range cannot span sheets".to_string()));
                        }
                        let sheet_name = self.graph.sheet_name(range_ref.start.sheet_id);
                        let sr0 = range_ref.start.coord.row();
                        let sc0 = range_ref.start.coord.col();
                        let er0 = range_ref.end.coord.row();
                        let ec0 = range_ref.end.coord.col();
                        if sr0 > er0 || sc0 > ec0 {
                            return Err(ExcelError::new(ExcelErrorKind::Ref)
                                .with_message("Invalid named range bounds".to_string()));
                        }

                        let h = (er0 - sr0 + 1) as usize;
                        let w = (ec0 - sc0 + 1) as usize;
                        let cell_count = (h as u64).saturating_mul(w as u64);
                        if cell_count > self.config.spill.max_spill_cells as u64 {
                            return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                                "Named range too large to materialize as an array".to_string(),
                            ));
                        }

                        let mut rows = Vec::with_capacity(h);
                        for r0 in sr0..=er0 {
                            let mut row = Vec::with_capacity(w);
                            for c0 in sc0..=ec0 {
                                let v = self
                                    .get_cell_value(sheet_name, r0 + 1, c0 + 1)
                                    .unwrap_or(LiteralValue::Empty);
                                row.push(v);
                            }
                            rows.push(row);
                        }
                        Ok(LiteralValue::Array(rows))
                    }
                    NamedDefinition::Cell(cell_ref) => {
                        let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                        let row = cell_ref.coord.row() + 1;
                        let col = cell_ref.coord.col() + 1;
                        let v = self
                            .get_cell_value(sheet_name, row, col)
                            .unwrap_or(LiteralValue::Empty);
                        Ok(LiteralValue::Array(vec![vec![v]]))
                    }
                    NamedDefinition::Literal(v) => Ok(LiteralValue::Array(vec![vec![v.clone()]])),
                    NamedDefinition::Formula { ast, .. } => {
                        let context_sheet = match named_range.scope {
                            NameScope::Sheet(id) => id,
                            NameScope::Workbook => sheet_id,
                        };
                        let sheet_name = self.graph.sheet_name(context_sheet);
                        let cell_ref = self
                            .graph
                            .get_cell_ref(vertex_id)
                            .unwrap_or_else(|| self.graph.make_cell_ref(sheet_name, 0, 0));
                        let interpreter = Interpreter::new_with_cell(self, sheet_name, cell_ref);
                        match interpreter.evaluate_ast(ast) {
                            Ok(cv) => {
                                let v = cv.into_literal();
                                match v {
                                    LiteralValue::Array(_) => Ok(v),
                                    other => Ok(LiteralValue::Array(vec![vec![other]])),
                                }
                            }
                            Err(err) => Ok(LiteralValue::Error(err)),
                        }
                    }
                };
            }
            VertexKind::InfiniteRange
            | VertexKind::Range
            | VertexKind::External
            | VertexKind::Table => {
                // Not directly evaluatable here.
                return Ok(LiteralValue::Number(0.0));
            }
        };

        // The interpreter uses a reference to the engine as the context
        let sheet_name = self.graph.sheet_name(sheet_id);
        let cell_ref = self
            .graph
            .get_cell_ref(vertex_id)
            .expect("cell ref for vertex");
        let interpreter = Interpreter::new_with_cell(self, sheet_name, cell_ref);

        interpreter
            .evaluate_arena_ast(ast_id, self.graph.data_store(), self.graph.sheet_reg())
            .map(|cv| cv.into_literal())
    }

    /// Get access to the shared thread pool for parallel evaluation
    pub fn thread_pool(&self) -> Option<&Arc<rayon::ThreadPool>> {
        self.thread_pool.as_ref()
    }
}

#[derive(Default)]
struct RowBoundsCache {
    snapshot: u64,
    // key: (sheet_id, col_idx)
    map: rustc_hash::FxHashMap<(u32, usize), (Option<u32>, Option<u32>)>,
}

impl RowBoundsCache {
    fn new(snapshot: u64) -> Self {
        Self {
            snapshot,
            map: Default::default(),
        }
    }
    fn get_row_bounds(
        &self,
        sheet_id: SheetId,
        col_idx: usize,
        snapshot: u64,
    ) -> Option<(Option<u32>, Option<u32>)> {
        if self.snapshot != snapshot {
            return None;
        }
        self.map.get(&(sheet_id as u32, col_idx)).copied()
    }
    fn put_row_bounds(
        &mut self,
        sheet_id: SheetId,
        col_idx: usize,
        snapshot: u64,
        bounds: (Option<u32>, Option<u32>),
    ) {
        if self.snapshot != snapshot {
            self.snapshot = snapshot;
            self.map.clear();
        }
        self.map.insert((sheet_id as u32, col_idx), bounds);
    }
}

struct UsedAxisBoundsCache {
    snapshot: u64,
    row_bounds_by_col_span: rustc_hash::FxHashMap<(SheetId, u32, u32), Option<(u32, u32)>>,
    col_bounds_by_row_span: rustc_hash::FxHashMap<(SheetId, u32, u32), Option<(u32, u32)>>,
    #[cfg(test)]
    row_hits: std::sync::atomic::AtomicUsize,
    #[cfg(test)]
    row_misses: std::sync::atomic::AtomicUsize,
    #[cfg(test)]
    col_hits: std::sync::atomic::AtomicUsize,
    #[cfg(test)]
    col_misses: std::sync::atomic::AtomicUsize,
}

impl UsedAxisBoundsCache {
    fn new(snapshot: u64) -> Self {
        Self {
            snapshot,
            row_bounds_by_col_span: Default::default(),
            col_bounds_by_row_span: Default::default(),
            #[cfg(test)]
            row_hits: std::sync::atomic::AtomicUsize::new(0),
            #[cfg(test)]
            row_misses: std::sync::atomic::AtomicUsize::new(0),
            #[cfg(test)]
            col_hits: std::sync::atomic::AtomicUsize::new(0),
            #[cfg(test)]
            col_misses: std::sync::atomic::AtomicUsize::new(0),
        }
    }

    fn reset_for_snapshot(&mut self, snapshot: u64) {
        if self.snapshot != snapshot {
            self.snapshot = snapshot;
            self.row_bounds_by_col_span.clear();
            self.col_bounds_by_row_span.clear();
        }
    }

    fn get_row_bounds(
        &self,
        sheet_id: SheetId,
        start_col: u32,
        end_col: u32,
        snapshot: u64,
    ) -> Option<Option<(u32, u32)>> {
        if self.snapshot != snapshot {
            return None;
        }
        let cached = self
            .row_bounds_by_col_span
            .get(&(sheet_id, start_col, end_col))
            .copied();
        #[cfg(test)]
        if cached.is_some() {
            self.row_hits.fetch_add(1, Ordering::Relaxed);
        }
        cached
    }

    fn put_row_bounds(
        &mut self,
        sheet_id: SheetId,
        start_col: u32,
        end_col: u32,
        snapshot: u64,
        bounds: Option<(u32, u32)>,
    ) {
        self.reset_for_snapshot(snapshot);
        self.row_bounds_by_col_span
            .insert((sheet_id, start_col, end_col), bounds);
        #[cfg(test)]
        self.row_misses.fetch_add(1, Ordering::Relaxed);
    }

    fn get_col_bounds(
        &self,
        sheet_id: SheetId,
        start_row: u32,
        end_row: u32,
        snapshot: u64,
    ) -> Option<Option<(u32, u32)>> {
        if self.snapshot != snapshot {
            return None;
        }
        let cached = self
            .col_bounds_by_row_span
            .get(&(sheet_id, start_row, end_row))
            .copied();
        #[cfg(test)]
        if cached.is_some() {
            self.col_hits.fetch_add(1, Ordering::Relaxed);
        }
        cached
    }

    fn put_col_bounds(
        &mut self,
        sheet_id: SheetId,
        start_row: u32,
        end_row: u32,
        snapshot: u64,
        bounds: Option<(u32, u32)>,
    ) {
        self.reset_for_snapshot(snapshot);
        self.col_bounds_by_row_span
            .insert((sheet_id, start_row, end_row), bounds);
        #[cfg(test)]
        self.col_misses.fetch_add(1, Ordering::Relaxed);
    }
}

// Phase 2 shim: in-process spill manager delegating to current graph methods.
#[derive(Default)]
pub struct ShimSpillManager {
    region_locks: RegionLockManager,
    pub(crate) active_locks: rustc_hash::FxHashMap<VertexId, u64>,
}

impl ShimSpillManager {
    pub(crate) fn reserve(
        &mut self,
        owner: VertexId,
        anchor_cell: CellRef,
        shape: SpillShape,
        _meta: SpillMeta,
    ) -> Result<(), ExcelError> {
        // Derive region from anchor + shape; enforce in-flight exclusivity only.
        let region = crate::engine::spill::Region {
            sheet_id: anchor_cell.sheet_id as u32,
            row_start: anchor_cell.coord.row(),
            row_end: anchor_cell
                .coord
                .row()
                .saturating_add(shape.rows)
                .saturating_sub(1),
            col_start: anchor_cell.coord.col(),
            col_end: anchor_cell
                .coord
                .col()
                .saturating_add(shape.cols)
                .saturating_sub(1),
        };
        match self.region_locks.reserve(region, owner) {
            Ok(id) => {
                if id != 0 {
                    self.active_locks.insert(owner, id);
                }
                Ok(())
            }
            Err(e) => Err(e),
        }
    }

    /// Release any in-flight region reservation still held for `owner`.
    ///
    /// Reservations are normally released on commit/rollback, but if an anchor is
    /// abandoned without committing (e.g. cycle detection stamps it with #CIRC), a
    /// stale reservation could remain. This is a no-op when nothing is held.
    pub(crate) fn release_owner(&mut self, owner: VertexId) {
        if let Some(id) = self.active_locks.remove(&owner) {
            self.region_locks.release(id);
        }
    }

    pub(crate) fn commit_array_with_value_probe<F>(
        &mut self,
        graph: &mut DependencyGraph,
        anchor_vertex: VertexId,
        targets: &[CellRef],
        rows: Vec<Vec<LiteralValue>>,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
        mut value_probe: F,
    ) -> Result<(), ExcelError>
    where
        F: FnMut(&DependencyGraph, &CellRef) -> Option<LiteralValue>,
    {
        use formualizer_common::{ExcelErrorExtra, ExcelErrorKind};

        // Re-run plan on concrete targets before committing to respect blockers.
        // This plan checks formula/spill ownership in the graph, but when the graph value cache
        // is disabled (Arrow-canonical mode), it cannot see non-empty value blockers.
        let plan_res = graph.plan_spill_region_allowing_formula_overwrite(
            anchor_vertex,
            targets,
            overwritable_formulas,
        );
        if let Err(e) = plan_res {
            if let Some(id) = self.active_locks.remove(&anchor_vertex) {
                self.region_locks.release(id);
            }
            return Err(e);
        }

        if !graph.value_cache_enabled() {
            // Compute expected spill shape from the target rectangle for diagnostics.
            let (expected_rows, expected_cols) = if targets.is_empty() {
                (0u32, 0u32)
            } else {
                let mut min_r = u32::MAX;
                let mut max_r = 0u32;
                let mut min_c = u32::MAX;
                let mut max_c = 0u32;
                for cell in targets {
                    let r = cell.coord.row();
                    let c = cell.coord.col();
                    min_r = min_r.min(r);
                    max_r = max_r.max(r);
                    min_c = min_c.min(c);
                    max_c = max_c.max(c);
                }
                (
                    max_r.saturating_sub(min_r).saturating_add(1),
                    max_c.saturating_sub(min_c).saturating_add(1),
                )
            };

            let anchor_cell = graph
                .get_cell_ref(anchor_vertex)
                .expect("anchor cell ref for spill commit");

            for cell in targets {
                // Never treat the anchor as a blocker.
                if *cell == anchor_cell {
                    continue;
                }
                // Skip cells already known to be owned by a spill; plan() handled spill conflicts.
                if graph.spill_registry_anchor_for_cell(*cell).is_some() {
                    continue;
                }
                // Skip formula vertices in the target region; plan() handled them (or allowed).
                if let Some(&vid) = graph.get_vertex_id_for_address(cell)
                    && vid != anchor_vertex
                {
                    match graph.get_vertex_kind(vid) {
                        crate::engine::vertex::VertexKind::FormulaScalar
                        | crate::engine::vertex::VertexKind::FormulaArray => {
                            // plan() already approved allowed overwrites.
                            continue;
                        }
                        _ => {}
                    }
                }

                if let Some(v) = value_probe(graph, cell)
                    && !matches!(v, LiteralValue::Empty)
                {
                    if let Some(id) = self.active_locks.remove(&anchor_vertex) {
                        self.region_locks.release(id);
                    }
                    return Err(ExcelError::new(ExcelErrorKind::Spill)
                        .with_message("BlockedByValue")
                        .with_extra(ExcelErrorExtra::Spill {
                            expected_rows,
                            expected_cols,
                        }));
                }
            }
        }

        let commit_res = graph.commit_spill_region_atomic_with_fault(
            anchor_vertex,
            targets.to_vec(),
            rows,
            None,
        );
        if let Some(id) = self.active_locks.remove(&anchor_vertex) {
            self.region_locks.release(id);
        }
        commit_res.map(|_| ())
    }

    /// Commit a spill and mirror all written cells into Arrow overlay via the owning engine.
    pub(crate) fn commit_array_with_overlay<R: EvaluationContext>(
        &mut self,
        engine: &mut Engine<R>,
        anchor_vertex: VertexId,
        targets: &[CellRef],
        rows: Vec<Vec<LiteralValue>>,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
    ) -> Result<(), ExcelError> {
        // Re-run plan on concrete targets before committing to respect blockers.
        let plan_res = engine.graph.plan_spill_region_allowing_formula_overwrite(
            anchor_vertex,
            targets,
            overwritable_formulas,
        );
        if let Err(e) = plan_res {
            if let Some(id) = self.active_locks.remove(&anchor_vertex) {
                self.region_locks.release(id);
            }
            return Err(e);
        }

        let commit_res = engine.graph.commit_spill_region_atomic_with_fault(
            anchor_vertex,
            targets.to_vec(),
            rows.clone(),
            None,
        );
        if let Some(id) = self.active_locks.remove(&anchor_vertex) {
            self.region_locks.release(id);
        }
        commit_res.map(|_| ())?;

        // Mirror into Arrow overlay when enabled
        if engine.config.arrow_storage_enabled
            && engine.config.delta_overlay_enabled
            && engine.config.write_formula_overlay_enabled
        {
            // Expect targets to be a contiguous rectangle row-major starting at some anchor
            for (idx, cell) in targets.iter().enumerate() {
                let (r_off, c_off) = {
                    if rows.is_empty() || rows[0].is_empty() {
                        (0usize, 0usize)
                    } else {
                        let width = rows[0].len();
                        (idx / width, idx % width)
                    }
                };
                let v = rows
                    .get(r_off)
                    .and_then(|r| r.get(c_off))
                    .cloned()
                    .unwrap_or(LiteralValue::Empty);
                let sheet_name = engine.graph.sheet_name(cell.sheet_id).to_string();
                engine.mirror_value_to_computed_overlay(
                    &sheet_name,
                    cell.coord.row() + 1,
                    cell.coord.col() + 1,
                    &v,
                );
            }
        }
        Ok(())
    }
}

impl<R> Engine<R>
where
    R: EvaluationContext,
{
    fn resolve_shared_ref(
        &self,
        reference: &ReferenceType,
        current_sheet: &str,
    ) -> Result<formualizer_common::SheetRef<'static>, ExcelError> {
        use formualizer_common::{
            SheetCellRef as SharedCellRef, SheetLocator, SheetRangeRef as SharedRangeRef,
            SheetRef as SharedRef,
        };

        // Preserve anchor flags from the parsed reference when possible.
        let sr = match reference {
            ReferenceType::Cell {
                sheet,
                row,
                col,
                row_abs,
                col_abs,
            } => {
                let row0 = row
                    .checked_sub(1)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                let col0 = col
                    .checked_sub(1)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                let sheet_loc = match sheet.as_deref() {
                    Some(name) => SheetLocator::from_name(name),
                    None => SheetLocator::Current,
                };
                let coord = formualizer_common::RelativeCoord::new(row0, col0, *row_abs, *col_abs);
                SharedRef::Cell(SharedCellRef::new(sheet_loc, coord))
            }
            ReferenceType::Range {
                sheet,
                start_row,
                start_col,
                end_row,
                end_col,
                start_row_abs,
                start_col_abs,
                end_row_abs,
                end_col_abs,
            } => {
                let sheet_loc = match sheet.as_deref() {
                    Some(name) => SheetLocator::from_name(name),
                    None => SheetLocator::Current,
                };
                let sr = start_row
                    .map(|r| {
                        r.checked_sub(1)
                            .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))
                    })
                    .transpose()?;
                let sc = start_col
                    .map(|c| {
                        c.checked_sub(1)
                            .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))
                    })
                    .transpose()?;
                let er = end_row
                    .map(|r| {
                        r.checked_sub(1)
                            .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))
                    })
                    .transpose()?;
                let ec = end_col
                    .map(|c| {
                        c.checked_sub(1)
                            .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))
                    })
                    .transpose()?;
                let range = SharedRangeRef::from_parts(
                    sheet_loc,
                    sr.map(|idx| formualizer_common::AxisBound::new(idx, *start_row_abs)),
                    sc.map(|idx| formualizer_common::AxisBound::new(idx, *start_col_abs)),
                    er.map(|idx| formualizer_common::AxisBound::new(idx, *end_row_abs)),
                    ec.map(|idx| formualizer_common::AxisBound::new(idx, *end_col_abs)),
                )
                .map_err(|_| ExcelError::new(ExcelErrorKind::Ref))?;
                SharedRef::Range(range)
            }
            _ => return Err(ExcelError::new(ExcelErrorKind::Ref)),
        };

        let current_id = self
            .graph
            .sheet_id(current_sheet)
            .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;

        let resolve_loc = |loc: SheetLocator<'_>| -> Result<SheetLocator<'static>, ExcelError> {
            match loc {
                SheetLocator::Current => Ok(SheetLocator::Id(current_id)),
                SheetLocator::Id(id) => Ok(SheetLocator::Id(id)),
                SheetLocator::Name(name) => {
                    let n = name.as_ref();
                    self.graph
                        .sheet_id(n)
                        .map(SheetLocator::Id)
                        .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))
                }
            }
        };

        match sr {
            SharedRef::Cell(cell) => {
                let owned = cell.into_owned();
                let sheet = resolve_loc(owned.sheet)?;
                Ok(SharedRef::Cell(SharedCellRef::new(sheet, owned.coord)))
            }
            SharedRef::Range(range) => {
                let owned = range.into_owned();
                let sheet = resolve_loc(owned.sheet)?;
                Ok(SharedRef::Range(SharedRangeRef {
                    sheet,
                    start_row: owned.start_row,
                    start_col: owned.start_col,
                    end_row: owned.end_row,
                    end_col: owned.end_col,
                }))
            }
        }
    }
}

// Implement the resolver traits for the Engine.
// This allows the interpreter to resolve references by querying the engine's graph.
impl<R> crate::traits::ReferenceResolver for Engine<R>
where
    R: EvaluationContext,
{
    fn resolve_cell_reference(
        &self,
        sheet: Option<&str>,
        row: u32,
        col: u32,
    ) -> Result<LiteralValue, ExcelError> {
        // This context-free trait method has no knowledge of the formula's
        // current sheet, so an unqualified (`None`) reference cannot be resolved
        // here. Previously this fell back to `default_sheet_name()`, which leaked
        // the reference onto an unrelated sheet (issue #110). Interpreter paths
        // already qualify references with the current sheet before reaching this
        // method (see `Interpreter::implicit_intersection_from_reference`), and
        // the sheet-aware scalar path goes through `resolve_cell_reference_value`
        // with an explicit `current_sheet`. Returning #REF! for an unqualified
        // reference here surfaces the missing context instead of silently
        // returning data from the wrong sheet.
        let Some(sheet_name) = sheet else {
            return Err(ExcelError::new(ExcelErrorKind::Ref).with_message(
                "Unqualified cell reference resolved without sheet context".to_string(),
            ));
        };
        // Prefer engine's unified accessor which consults Arrow store for base values
        // and falls back to graph for formulas and stored values.
        if let Some(v) = self.get_cell_value(sheet_name, row, col) {
            Ok(v)
        } else {
            // Excel semantics: empty cell coerces to 0 in numeric contexts
            Ok(LiteralValue::Number(0.0))
        }
    }
}

impl<R> crate::traits::RangeResolver for Engine<R>
where
    R: EvaluationContext,
{
    fn resolve_range_reference(
        &self,
        sheet: Option<&str>,
        sr: Option<u32>,
        sc: Option<u32>,
        er: Option<u32>,
        ec: Option<u32>,
    ) -> Result<Box<dyn crate::traits::Range>, ExcelError> {
        // For now, delegate range resolution to the external resolver.
        // A future optimization could be to handle this within the graph.
        self.resolver.resolve_range_reference(sheet, sr, sc, er, ec)
    }
}

impl<R> crate::traits::NamedRangeResolver for Engine<R>
where
    R: EvaluationContext,
{
    fn resolve_named_range_reference(
        &self,
        name: &str,
    ) -> Result<Vec<Vec<LiteralValue>>, ExcelError> {
        self.resolver.resolve_named_range_reference(name)
    }
}

impl<R> crate::traits::TableResolver for Engine<R>
where
    R: EvaluationContext,
{
    fn resolve_table_reference(
        &self,
        tref: &formualizer_parse::parser::TableReference,
    ) -> Result<Box<dyn crate::traits::Table>, ExcelError> {
        self.resolver.resolve_table_reference(tref)
    }
}

impl<R> crate::traits::SourceResolver for Engine<R>
where
    R: EvaluationContext,
{
    fn source_scalar_version(&self, name: &str) -> Option<u64> {
        self.resolver.source_scalar_version(name)
    }

    fn resolve_source_scalar(&self, name: &str) -> Result<LiteralValue, ExcelError> {
        self.resolver.resolve_source_scalar(name)
    }

    fn source_table_version(&self, name: &str) -> Option<u64> {
        self.resolver.source_table_version(name)
    }

    fn resolve_source_table(
        &self,
        name: &str,
    ) -> Result<Box<dyn crate::traits::Table>, ExcelError> {
        self.resolver.resolve_source_table(name)
    }
}

// The Engine is a Resolver because it implements the constituent traits.
impl<R> crate::traits::Resolver for Engine<R> where R: EvaluationContext {}

// The Engine provides functions by delegating to its internal resolver.
impl<R> crate::traits::FunctionProvider for Engine<R>
where
    R: EvaluationContext,
{
    fn get_function(
        &self,
        prefix: &str,
        name: &str,
    ) -> Option<std::sync::Arc<dyn crate::function::Function>> {
        self.resolver.get_function(prefix, name)
    }
}

// Override EvaluationContext to provide thread pool access
impl<R> crate::traits::EvaluationContext for Engine<R>
where
    R: EvaluationContext,
{
    fn clock(&self) -> &dyn crate::timezone::ClockProvider {
        &self.clock
    }

    fn thread_pool(&self) -> Option<&Arc<rayon::ThreadPool>> {
        self.thread_pool.as_ref()
    }

    fn cancellation_token(&self) -> Option<Arc<std::sync::atomic::AtomicBool>> {
        self.active_cancel_flag.clone()
    }

    fn chunk_hint(&self) -> Option<usize> {
        // Use a simple heuristic from configuration (stripe width * height) as a default hint.
        let hint =
            (self.config.stripe_height as usize).saturating_mul(self.config.stripe_width as usize);
        Some(hint.clamp(1024, 1 << 20)) // clamp between 1K and ~1M
    }

    fn volatile_level(&self) -> crate::traits::VolatileLevel {
        self.config.volatile_level
    }

    fn workbook_seed(&self) -> u64 {
        self.config.workbook_seed
    }

    fn recalc_epoch(&self) -> u64 {
        self.recalc_epoch
    }

    fn workbook_sheet_count(&self) -> Option<usize> {
        Some(self.graph.sheet_reg().active_len())
    }

    fn sheet_index_by_name(&self, sheet: &str) -> Option<usize> {
        self.graph.sheet_reg().active_position(sheet)
    }

    fn current_sheet_index(&self, current_sheet: &str) -> Option<usize> {
        self.sheet_index_by_name(current_sheet)
    }

    fn inspect_reference(
        &self,
        reference: &ReferenceType,
        current_sheet: &str,
    ) -> Result<Option<ReferenceInfo>, ExcelError> {
        let sheet_info = |sheet_name: &str| -> Result<(SheetId, usize), ExcelError> {
            let sheet_id = self
                .graph
                .sheet_id(sheet_name)
                .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
            let sheet_index = self
                .graph
                .sheet_reg()
                .active_position_by_id(sheet_id)
                .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
            Ok((sheet_id, sheet_index))
        };

        let cell_info =
            |sheet_name: &str, row: u32, col: u32| -> Result<ReferenceInfo, ExcelError> {
                let (sheet_id, sheet_index) = sheet_info(sheet_name)?;
                let row0 = row
                    .checked_sub(1)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                let col0 = col
                    .checked_sub(1)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                Ok(ReferenceInfo {
                    first_sheet_index: Some(sheet_index),
                    sheet_count: Some(1),
                    first_cell: Some(CellRef::new(sheet_id, Coord::new(row0, col0, true, true))),
                })
            };

        let range_info = |sheet_name: &str,
                          start_row: Option<u32>,
                          start_col: Option<u32>|
         -> Result<ReferenceInfo, ExcelError> {
            let (sheet_id, sheet_index) = sheet_info(sheet_name)?;
            let row = start_row.unwrap_or(1);
            let col = start_col.unwrap_or(1);
            let row0 = row
                .checked_sub(1)
                .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
            let col0 = col
                .checked_sub(1)
                .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
            Ok(ReferenceInfo {
                first_sheet_index: Some(sheet_index),
                sheet_count: Some(1),
                first_cell: Some(CellRef::new(sheet_id, Coord::new(row0, col0, true, true))),
            })
        };

        let info = match reference {
            ReferenceType::Cell {
                sheet, row, col, ..
            } => {
                let sheet_name = sheet.as_deref().unwrap_or(current_sheet);
                cell_info(sheet_name, *row, *col)?
            }
            ReferenceType::Range {
                sheet,
                start_row,
                start_col,
                ..
            } => {
                let sheet_name = sheet.as_deref().unwrap_or(current_sheet);
                range_info(sheet_name, *start_row, *start_col)?
            }
            ReferenceType::Cell3D {
                sheet_first,
                sheet_last,
                row,
                col,
                ..
            } => {
                let first = cell_info(sheet_first, *row, *col)?;
                ReferenceInfo {
                    first_sheet_index: first.first_sheet_index,
                    sheet_count: self
                        .graph
                        .sheet_reg()
                        .active_span_len(sheet_first, sheet_last),
                    first_cell: first.first_cell,
                }
            }
            ReferenceType::Range3D {
                sheet_first,
                sheet_last,
                start_row,
                start_col,
                ..
            } => {
                let first = range_info(sheet_first, *start_row, *start_col)?;
                ReferenceInfo {
                    first_sheet_index: first.first_sheet_index,
                    sheet_count: self
                        .graph
                        .sheet_reg()
                        .active_span_len(sheet_first, sheet_last),
                    first_cell: first.first_cell,
                }
            }
            ReferenceType::NamedRange(name) => {
                let current_id = self
                    .graph
                    .sheet_id(current_sheet)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                let named = self
                    .graph
                    .resolve_name_entry(name, current_id)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                match &named.definition {
                    NamedDefinition::Cell(cell) => ReferenceInfo {
                        first_sheet_index: self
                            .graph
                            .sheet_reg()
                            .active_position_by_id(cell.sheet_id),
                        sheet_count: Some(1),
                        first_cell: Some(*cell),
                    },
                    NamedDefinition::Range(range) => ReferenceInfo {
                        first_sheet_index: self
                            .graph
                            .sheet_reg()
                            .active_position_by_id(range.start.sheet_id),
                        sheet_count: Some(1),
                        first_cell: Some(range.start),
                    },
                    NamedDefinition::Literal(_) | NamedDefinition::Formula { .. } => {
                        ReferenceInfo {
                            first_sheet_index: None,
                            sheet_count: None,
                            first_cell: None,
                        }
                    }
                }
            }
            ReferenceType::Table(tref) => {
                let table = self
                    .graph
                    .resolve_table_entry(&tref.name)
                    .ok_or_else(|| ExcelError::new(ExcelErrorKind::Ref))?;
                ReferenceInfo {
                    first_sheet_index: self
                        .graph
                        .sheet_reg()
                        .active_position_by_id(table.range.start.sheet_id),
                    sheet_count: Some(1),
                    first_cell: Some(table.range.start),
                }
            }
            ReferenceType::External(_) => return Err(ExcelError::new(ExcelErrorKind::Ref)),
        };

        Ok(Some(info))
    }

    fn formula_text_at_cell(&self, cell: CellRef) -> Result<Option<String>, ExcelError> {
        let sheet_name = self.graph.sheet_name(cell.sheet_id);
        if sheet_name.is_empty() {
            return Err(ExcelError::new(ExcelErrorKind::Ref));
        }
        let row = cell.coord.row() + 1;
        let col = cell.coord.col() + 1;

        if let Some(entries) = self.staged_formulas.get(sheet_name)
            && let Some(text) = entries.get(row, col)
        {
            return Ok(Some(if text.starts_with('=') {
                text.to_owned()
            } else {
                format!("={text}")
            }));
        }

        let Some(vertex) = self.graph.get_vertex_for_cell(&cell) else {
            return Ok(None);
        };
        let Some(ast) = self.graph.get_formula(vertex) else {
            return Ok(None);
        };
        Ok(Some(formualizer_parse::pretty::canonical_formula(&ast)))
    }

    fn used_rows_for_columns(
        &self,
        sheet: &str,
        start_col: u32,
        end_col: u32,
    ) -> Option<(u32, u32)> {
        // Union Arrow-backed used-region with formula rows that have not been materialized yet.
        let sheet_id = self.graph.sheet_id(sheet)?;
        let snap = self.data_snapshot_id();
        if let Some(cached) = self.used_axis_bounds_cache.read().ok().and_then(|guard| {
            guard
                .as_ref()
                .and_then(|cache| cache.get_row_bounds(sheet_id, start_col, end_col, snap))
        }) {
            return cached;
        }

        let arrow_bounds = self
            .sheet_store()
            .sheet(sheet)
            .and_then(|_| self.arrow_used_row_bounds(sheet, start_col, end_col));
        let formula_bounds = self.formula_row_bounds_for_columns(sheet, start_col, end_col);
        let computed = if let Some(bounds) = Self::union_used_bounds(arrow_bounds, formula_bounds) {
            Some(bounds)
        } else {
            let sc0 = start_col.saturating_sub(1);
            let ec0 = end_col.saturating_sub(1);
            self.graph
                .used_row_bounds_for_columns(sheet_id, sc0, ec0)
                .map(|(a0, b0)| (a0 + 1, b0 + 1))
        };

        if let Ok(mut guard) = self.used_axis_bounds_cache.write() {
            guard
                .get_or_insert_with(|| UsedAxisBoundsCache::new(snap))
                .put_row_bounds(sheet_id, start_col, end_col, snap, computed);
        }

        computed
    }

    fn used_cols_for_rows(&self, sheet: &str, start_row: u32, end_row: u32) -> Option<(u32, u32)> {
        // Union Arrow-backed used-region with formula columns that have not been materialized yet.
        let sheet_id = self.graph.sheet_id(sheet)?;
        let snap = self.data_snapshot_id();
        if let Some(cached) = self.used_axis_bounds_cache.read().ok().and_then(|guard| {
            guard
                .as_ref()
                .and_then(|cache| cache.get_col_bounds(sheet_id, start_row, end_row, snap))
        }) {
            return cached;
        }

        let arrow_bounds = self
            .sheet_store()
            .sheet(sheet)
            .and_then(|_| self.arrow_used_col_bounds(sheet, start_row, end_row));
        let formula_bounds = self.formula_col_bounds_for_rows(sheet, start_row, end_row);
        let computed = if let Some(bounds) = Self::union_used_bounds(arrow_bounds, formula_bounds) {
            Some(bounds)
        } else {
            let sr0 = start_row.saturating_sub(1);
            let er0 = end_row.saturating_sub(1);
            self.graph
                .used_col_bounds_for_rows(sheet_id, sr0, er0)
                .map(|(a0, b0)| (a0 + 1, b0 + 1))
        };

        if let Ok(mut guard) = self.used_axis_bounds_cache.write() {
            guard
                .get_or_insert_with(|| UsedAxisBoundsCache::new(snap))
                .put_col_bounds(sheet_id, start_row, end_row, snap, computed);
        }

        computed
    }

    fn sheet_bounds(&self, sheet: &str) -> Option<(u32, u32)> {
        let _ = self.graph.sheet_id(sheet)?;
        // Excel-like upper bounds; we expose something finite but large.
        // Backends may override with real bounds.
        Some((1_048_576, 16_384)) // 1048576 rows, 16384 cols (XFD)
    }

    fn data_snapshot_id(&self) -> u64 {
        self.snapshot_id.load(std::sync::atomic::Ordering::Relaxed)
    }

    fn backend_caps(&self) -> crate::traits::BackendCaps {
        crate::traits::BackendCaps {
            streaming: true,
            used_region: true,
            write: false,
            tables: false,
            async_stream: false,
        }
    }

    fn build_lookup_index(
        &self,
        view: &RangeView<'_>,
        axis: LookupAxis,
    ) -> Option<Arc<LookupIndex>> {
        self.build_lookup_index_impl(view, axis)
    }

    // Flats removed

    fn date_system(&self) -> crate::engine::DateSystem {
        self.config.date_system
    }
    /// New: resolve a reference into a RangeView (Phase 2 API)
    fn resolve_range_view<'c>(
        &'c self,
        reference: &ReferenceType,
        current_sheet: &str,
    ) -> Result<RangeView<'c>, ExcelError> {
        match reference {
            ReferenceType::External(ext) => {
                let name = ext.raw.as_str();
                match ext.kind {
                    formualizer_parse::parser::ExternalRefKind::Cell { .. } => {
                        let Some(source) = self.graph.resolve_source_scalar_entry(name) else {
                            return Err(ExcelError::new(ExcelErrorKind::Name)
                                .with_message(format!("Undefined name: {name}")));
                        };
                        let version = source
                            .version
                            .or_else(|| self.resolver.source_scalar_version(name));
                        let v = self.resolve_source_scalar_cached(name, version)?;
                        Ok(RangeView::from_owned_rows(
                            vec![vec![v]],
                            self.config.date_system,
                        ))
                    }
                    formualizer_parse::parser::ExternalRefKind::Range { .. } => {
                        let Some(source) = self.graph.resolve_source_table_entry(name) else {
                            return Err(ExcelError::new(ExcelErrorKind::Name)
                                .with_message(format!("Undefined table: {name}")));
                        };
                        let version = source
                            .version
                            .or_else(|| self.resolver.source_table_version(name));
                        let table = self.resolve_source_table_cached(name, version)?;
                        let spec = Some(formualizer_parse::parser::TableSpecifier::Data);
                        self.source_table_to_range_view(table.as_ref(), &spec)
                    }
                }
            }
            ReferenceType::Range { .. } => {
                let shared = self.resolve_shared_ref(reference, current_sheet)?;
                let formualizer_common::SheetRef::Range(range) = shared else {
                    return Err(ExcelError::new(ExcelErrorKind::Ref));
                };
                let sheet_id = match range.sheet {
                    formualizer_common::SheetLocator::Id(id) => id,
                    _ => return Err(ExcelError::new(ExcelErrorKind::Ref)),
                };
                let sheet_name = self.graph.sheet_name(sheet_id);

                let bounded_range = if range.start_row.is_some()
                    && range.start_col.is_some()
                    && range.end_row.is_some()
                    && range.end_col.is_some()
                {
                    Some(RangeRef::try_from_shared(range.as_ref())?)
                } else {
                    None
                };

                let mut sr = bounded_range
                    .as_ref()
                    .map(|r| r.start.coord.row() + 1)
                    .or_else(|| range.start_row.map(|b| b.index + 1));
                let mut sc = bounded_range
                    .as_ref()
                    .map(|r| r.start.coord.col() + 1)
                    .or_else(|| range.start_col.map(|b| b.index + 1));
                let mut er = bounded_range
                    .as_ref()
                    .map(|r| r.end.coord.row() + 1)
                    .or_else(|| range.end_row.map(|b| b.index + 1));
                let mut ec = bounded_range
                    .as_ref()
                    .map(|r| r.end.coord.col() + 1)
                    .or_else(|| range.end_col.map(|b| b.index + 1));

                if sr.is_none() && er.is_none() {
                    // Full-column reference: anchor at row 1
                    let scv = sc.unwrap_or(1);
                    let ecv = ec.unwrap_or(scv);
                    sr = Some(1);
                    if let Some((_, max_r)) = self.used_rows_for_columns(sheet_name, scv, ecv) {
                        er = Some(max_r);
                    } else if let Some((max_rows, _)) = self.sheet_bounds(sheet_name) {
                        er = Some(self.config.max_open_ended_rows);
                    }
                }
                if sc.is_none() && ec.is_none() {
                    // Full-row reference: anchor at column 1
                    let srv = sr.unwrap_or(1);
                    let erv = er.unwrap_or(srv);
                    sc = Some(1);
                    if let Some((_, max_c)) = self.used_cols_for_rows(sheet_name, srv, erv) {
                        ec = Some(max_c);
                    } else if let Some((_, max_cols)) = self.sheet_bounds(sheet_name) {
                        ec = Some(self.config.max_open_ended_cols);
                    }
                }
                if sr.is_some() && er.is_none() {
                    let scv = sc.unwrap_or(1);
                    let ecv = ec.unwrap_or(scv);
                    if let Some((_, max_r)) = self.used_rows_for_columns(sheet_name, scv, ecv) {
                        er = Some(max_r);
                    } else if let Some((max_rows, _)) = self.sheet_bounds(sheet_name) {
                        er = Some(self.config.max_open_ended_rows);
                    }
                }
                if er.is_some() && sr.is_none() {
                    // Open start: anchor at row 1
                    sr = Some(1);
                }
                if sc.is_some() && ec.is_none() {
                    let srv = sr.unwrap_or(1);
                    let erv = er.unwrap_or(srv);
                    if let Some((_, max_c)) = self.used_cols_for_rows(sheet_name, srv, erv) {
                        ec = Some(max_c);
                    } else if let Some((_, max_cols)) = self.sheet_bounds(sheet_name) {
                        ec = Some(self.config.max_open_ended_cols);
                    }
                }
                if ec.is_some() && sc.is_none() {
                    // Open start: anchor at column 1
                    sc = Some(1);
                }

                let sr = sr.unwrap_or(1);
                let sc = sc.unwrap_or(1);
                let er = er.unwrap_or(sr.saturating_sub(1));
                let ec = ec.unwrap_or(sc.saturating_sub(1));

                if self.force_materialize_range_views {
                    if er < sr || ec < sc {
                        return Ok(RangeView::from_owned_rows(
                            Vec::new(),
                            self.config.date_system,
                        ));
                    }
                    let h = (er - sr + 1) as u64;
                    let w = (ec - sc + 1) as u64;
                    let cell_count = h.saturating_mul(w);
                    if cell_count <= self.config.spill.max_spill_cells as u64 {
                        let mut rows: Vec<Vec<LiteralValue>> = Vec::with_capacity(h as usize);
                        for r in sr..=er {
                            let mut rowv: Vec<LiteralValue> = Vec::with_capacity(w as usize);
                            for c in sc..=ec {
                                rowv.push(
                                    self.get_cell_value(sheet_name, r, c)
                                        .unwrap_or(LiteralValue::Empty),
                                );
                            }
                            rows.push(rowv);
                        }
                        return Ok(RangeView::from_owned_rows(rows, self.config.date_system));
                    }
                }

                let Some(asheet) = self.sheet_store().sheet(sheet_name) else {
                    return Ok(RangeView::from_owned_rows(
                        Vec::new(),
                        self.config.date_system,
                    ));
                };

                let rv = if er < sr || ec < sc {
                    asheet.range_view(1, 1, 0, 0)
                } else {
                    let sr0 = sr.saturating_sub(1) as usize;
                    let sc0 = sc.saturating_sub(1) as usize;
                    let er0 = er.saturating_sub(1) as usize;
                    let ec0 = ec.saturating_sub(1) as usize;
                    asheet.range_view(sr0, sc0, er0, ec0)
                };

                Ok(rv)
            }
            ReferenceType::Cell { .. } => {
                let shared = self.resolve_shared_ref(reference, current_sheet)?;
                let formualizer_common::SheetRef::Cell(cell) = shared else {
                    return Err(ExcelError::new(ExcelErrorKind::Ref));
                };
                let addr = CellRef::try_from_shared(cell)?;
                let sheet_id = addr.sheet_id;
                let sheet_name = self.graph.sheet_name(sheet_id);
                let row = addr.coord.row() + 1;
                let col = addr.coord.col() + 1;

                if self.force_materialize_range_views {
                    let v = self
                        .get_cell_value(sheet_name, row, col)
                        .unwrap_or(LiteralValue::Empty);
                    return Ok(RangeView::from_owned_rows(
                        vec![vec![v]],
                        self.config.date_system,
                    ));
                }

                if let Some(asheet) = self.sheet_store().sheet(sheet_name) {
                    let r0 = row.saturating_sub(1) as usize;
                    let c0 = col.saturating_sub(1) as usize;
                    let rv = asheet.range_view(r0, c0, r0, c0);
                    Ok(rv)
                } else {
                    let v = self
                        .get_cell_value(sheet_name, row, col)
                        .unwrap_or(LiteralValue::Empty);
                    Ok(RangeView::from_owned_rows(
                        vec![vec![v]],
                        self.config.date_system,
                    ))
                }
            }
            ReferenceType::NamedRange(name) => {
                if let Some(current_id) = self.graph.sheet_id(current_sheet)
                    && let Some(named) = self.graph.resolve_name_entry(name, current_id)
                {
                    match &named.definition {
                        NamedDefinition::Cell(cell_ref) => {
                            let sheet_name = self.graph.sheet_name(cell_ref.sheet_id);
                            if self.force_materialize_range_views {
                                let v = self
                                    .get_cell_value(
                                        sheet_name,
                                        cell_ref.coord.row() + 1,
                                        cell_ref.coord.col() + 1,
                                    )
                                    .unwrap_or(LiteralValue::Empty);
                                return Ok(RangeView::from_owned_rows(
                                    vec![vec![v]],
                                    self.config.date_system,
                                ));
                            } else {
                                let asheet = self
                                    .sheet_store()
                                    .sheet(sheet_name)
                                    .expect("Arrow sheet missing for named cell");
                                let r0 = cell_ref.coord.row() as usize;
                                let c0 = cell_ref.coord.col() as usize;
                                let rv = asheet.range_view(r0, c0, r0, c0);
                                return Ok(rv);
                            }
                        }
                        NamedDefinition::Range(range_ref) => {
                            let sheet_name = self.graph.sheet_name(range_ref.start.sheet_id);
                            let sr = range_ref.start.coord.row() + 1;
                            let sc = range_ref.start.coord.col() + 1;
                            let er = range_ref.end.coord.row() + 1;
                            let ec = range_ref.end.coord.col() + 1;
                            if self.force_materialize_range_views {
                                let h = (er.saturating_sub(sr) + 1) as u64;
                                let w = (ec.saturating_sub(sc) + 1) as u64;
                                let cell_count = h.saturating_mul(w);
                                if cell_count <= self.config.spill.max_spill_cells as u64 {
                                    let mut rows: Vec<Vec<LiteralValue>> =
                                        Vec::with_capacity(h as usize);
                                    for r in sr..=er {
                                        let mut rowv: Vec<LiteralValue> =
                                            Vec::with_capacity(w as usize);
                                        for c in sc..=ec {
                                            rowv.push(
                                                self.get_cell_value(sheet_name, r, c)
                                                    .unwrap_or(LiteralValue::Empty),
                                            );
                                        }
                                        rows.push(rowv);
                                    }
                                    return Ok(RangeView::from_owned_rows(
                                        rows,
                                        self.config.date_system,
                                    ));
                                }
                            }
                            let asheet = self
                                .sheet_store()
                                .sheet(sheet_name)
                                .expect("Arrow sheet missing for named range");
                            let sr0 = range_ref.start.coord.row() as usize;
                            let sc0 = range_ref.start.coord.col() as usize;
                            let er0 = range_ref.end.coord.row() as usize;
                            let ec0 = range_ref.end.coord.col() as usize;
                            let rv = asheet.range_view(sr0, sc0, er0, ec0);
                            return Ok(rv);
                        }
                        NamedDefinition::Literal(v) => {
                            return Ok(RangeView::from_owned_rows(
                                vec![vec![v.clone()]],
                                self.config.date_system,
                            ));
                        }
                        NamedDefinition::Formula { .. } => {
                            if let Some(value) = self.graph.get_value(named.vertex) {
                                return Ok(RangeView::from_owned_rows(
                                    vec![vec![value]],
                                    self.config.date_system,
                                ));
                            }
                        }
                    }
                }

                if let Some(source) = self.graph.resolve_source_scalar_entry(name) {
                    let version = source
                        .version
                        .or_else(|| self.resolver.source_scalar_version(name));
                    let v = self.resolve_source_scalar_cached(name, version)?;
                    return Ok(RangeView::from_owned_rows(
                        vec![vec![v]],
                        self.config.date_system,
                    ));
                }

                let data = self.resolver.resolve_named_range_reference(name)?;
                Ok(RangeView::from_owned_rows(data, self.config.date_system))
            }
            ReferenceType::Table(tref) => {
                if let Some(table) = self.graph.resolve_table_entry(&tref.name) {
                    let sheet_name = self.graph.sheet_name(table.range.start.sheet_id);
                    let asheet = self
                        .sheet_store()
                        .sheet(sheet_name)
                        .expect("Arrow sheet missing for table reference");

                    let sr0 = table.range.start.coord.row() as usize;
                    let sc0 = table.range.start.coord.col() as usize;
                    let er0 = table.range.end.coord.row() as usize;
                    let ec0 = table.range.end.coord.col() as usize;

                    let has_totals = table.totals_row;
                    let has_headers = table.header_row;
                    let data_sr = if has_headers {
                        sr0.saturating_add(1)
                    } else {
                        sr0
                    };
                    let data_er = if has_totals {
                        er0.saturating_sub(1)
                    } else {
                        er0
                    };

                    let select = |sr: usize, sc: usize, er: usize, ec: usize| {
                        if sr > er || sc > ec {
                            asheet.range_view(1, 1, 0, 0)
                        } else {
                            asheet.range_view(sr, sc, er, ec)
                        }
                    };

                    let av = match &tref.specifier {
                        None => {
                            return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                                "Table reference without specifier is unsupported".to_string(),
                            ));
                        }
                        Some(formualizer_parse::parser::TableSpecifier::Column(col)) => {
                            let Some(idx) = table.col_index(col) else {
                                return Err(ExcelError::new(ExcelErrorKind::Ref).with_message(
                                    "Column refers to unknown table column".to_string(),
                                ));
                            };
                            let c0 = sc0 + idx;
                            select(data_sr, c0, data_er, c0)
                        }
                        Some(formualizer_parse::parser::TableSpecifier::ColumnRange(
                            start,
                            end,
                        )) => {
                            let Some(si) = table.col_index(start) else {
                                return Err(ExcelError::new(ExcelErrorKind::Ref).with_message(
                                    "Column range refers to unknown column(s)".to_string(),
                                ));
                            };
                            let Some(ei) = table.col_index(end) else {
                                return Err(ExcelError::new(ExcelErrorKind::Ref).with_message(
                                    "Column range refers to unknown column(s)".to_string(),
                                ));
                            };
                            let (mut a, mut b) = (si, ei);
                            if a > b {
                                std::mem::swap(&mut a, &mut b);
                            }
                            let c_start = sc0 + a;
                            let c_end = sc0 + b;
                            select(data_sr, c_start, data_er, c_end)
                        }
                        Some(formualizer_parse::parser::TableSpecifier::All)
                        | Some(formualizer_parse::parser::TableSpecifier::SpecialItem(
                            formualizer_parse::parser::SpecialItem::All,
                        )) => select(sr0, sc0, er0, ec0),
                        Some(formualizer_parse::parser::TableSpecifier::Data)
                        | Some(formualizer_parse::parser::TableSpecifier::SpecialItem(
                            formualizer_parse::parser::SpecialItem::Data,
                        )) => select(data_sr, sc0, data_er, ec0),
                        Some(formualizer_parse::parser::TableSpecifier::Headers)
                        | Some(formualizer_parse::parser::TableSpecifier::SpecialItem(
                            formualizer_parse::parser::SpecialItem::Headers,
                        )) => {
                            if !has_headers {
                                asheet.range_view(1, 1, 0, 0)
                            } else {
                                select(sr0, sc0, sr0, ec0)
                            }
                        }
                        Some(formualizer_parse::parser::TableSpecifier::Totals)
                        | Some(formualizer_parse::parser::TableSpecifier::SpecialItem(
                            formualizer_parse::parser::SpecialItem::Totals,
                        )) => {
                            if !has_totals {
                                asheet.range_view(1, 1, 0, 0)
                            } else {
                                select(er0, sc0, er0, ec0)
                            }
                        }
                        Some(formualizer_parse::parser::TableSpecifier::SpecialItem(
                            formualizer_parse::parser::SpecialItem::ThisRow,
                        )) => {
                            return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                                "@ (This Row) requires table-aware context; not yet supported"
                                    .to_string(),
                            ));
                        }
                        Some(formualizer_parse::parser::TableSpecifier::Row(_))
                        | Some(formualizer_parse::parser::TableSpecifier::Combination(_)) => {
                            return Err(ExcelError::new(ExcelErrorKind::NImpl).with_message(
                                "Complex structured references not yet supported".to_string(),
                            ));
                        }
                    };

                    return Ok(av);
                }

                if let Some(source) = self.graph.resolve_source_table_entry(&tref.name) {
                    let version = source
                        .version
                        .or_else(|| self.resolver.source_table_version(&tref.name));
                    let table = self.resolve_source_table_cached(&tref.name, version)?;
                    return self.source_table_to_range_view(table.as_ref(), &tref.specifier);
                }

                // Fallback: materialize via Resolver::resolve_range_like tranche 1
                let boxed = self.resolve_range_like(&ReferenceType::Table(tref.clone()))?;
                let owned = boxed.materialise().into_owned();
                Ok(RangeView::from_owned_rows(owned, self.config.date_system))
            }
            ReferenceType::Cell3D { .. } | ReferenceType::Range3D { .. } => {
                Err(ExcelError::new(ExcelErrorKind::NImpl)
                    .with_message("3D references are not yet supported".to_string()))
            }
        }
    }

    fn resolve_cell_reference_value(
        &self,
        sheet: Option<&str>,
        row: u32,
        col: u32,
        current_sheet: &str,
    ) -> Result<LiteralValue, ExcelError> {
        let sheet_name = sheet.unwrap_or(current_sheet);
        if self.graph.sheet_id(sheet_name).is_none() {
            return Err(ExcelError::new(ExcelErrorKind::Ref));
        }
        Ok(self
            .get_cell_value(sheet_name, row, col)
            .unwrap_or(LiteralValue::Empty))
    }

    fn build_criteria_mask(
        &self,
        view: &RangeView<'_>,
        col_in_view: usize,
        pred: &crate::args::CriteriaPredicate,
    ) -> Option<std::sync::Arc<arrow_array::BooleanArray>> {
        if view.dims().1 == 0 {
            return None;
        }
        // If the view is logically open-ended but the backing sheet has no physical rows,
        // treat the mask as empty (0-len) rather than attempting to build a huge mask.
        let sheet_rows = view.sheet().nrows as usize;
        if sheet_rows == 0 || view.start_row() >= sheet_rows {
            return Some(std::sync::Arc::new(arrow_array::BooleanArray::new_null(0)));
        }
        compute_criteria_mask(view, col_in_view, pred)
    }

    fn build_row_visibility_mask(
        &self,
        view: &RangeView<'_>,
        mode: VisibilityMaskMode,
    ) -> Option<std::sync::Arc<arrow_array::BooleanArray>> {
        self.build_row_visibility_mask_for_view(view, mode)
    }
}

impl<R> Engine<R>
where
    R: EvaluationContext,
{
    fn clear_spill_projection_and_mirror(
        &mut self,
        anchor_vertex: VertexId,
        delta: Option<&mut DeltaCollector>,
    ) {
        let spill_cells = self
            .graph
            .spill_cells_for_anchor(anchor_vertex)
            .map(|cells| cells.to_vec())
            .unwrap_or_default();
        if spill_cells.is_empty() {
            return;
        }

        if let Some(delta) = delta
            && delta.mode != DeltaMode::Off
        {
            let empty = LiteralValue::Empty;
            for cell in spill_cells.iter() {
                let sheet_name = self.graph.sheet_name(cell.sheet_id);
                let old = self
                    .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                    .unwrap_or(LiteralValue::Empty);
                if old != empty {
                    delta.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                }
            }
        }

        self.graph.clear_spill_region(anchor_vertex);
        if let Some(scope) = Self::formula_plane_region_from_cells(&spill_cells) {
            self.record_formula_plane_structural_change(scope);
        }

        if self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled
        {
            let empty = LiteralValue::Empty;
            for cell in spill_cells.iter() {
                let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                self.mirror_value_to_computed_overlay(
                    &sheet_name,
                    cell.coord.row() + 1,
                    cell.coord.col() + 1,
                    &empty,
                );
            }
        }
    }

    /// Apply the evaluation outcome for one cyclic SCC: stamp `#CIRC!` on its
    /// (optionally filtered) members via `stamp_cycle_error`.
    ///
    /// This is the single per-SCC application point used by every schedule
    /// consumer walking `Schedule::units` (pre-work for #112, where cyclic
    /// SCCs will gain runtime verdicts instead of an unconditional stamp).
    ///
    /// `dirty_filter` preserves the recalc-plan quirk: when `Some(dirty)`,
    /// only members present in the set are stamped.
    ///
    /// Returns the number of vertices stamped (0 when a filter excludes every
    /// member), so callers can keep their site-specific `cycle_errors`
    /// accounting.
    fn apply_cycle_outcome(
        &mut self,
        cycle: &[VertexId],
        mut delta: Option<&mut DeltaCollector>,
        dirty_filter: Option<&FxHashSet<VertexId>>,
    ) -> usize {
        let circ_error = LiteralValue::Error(
            ExcelError::new(ExcelErrorKind::Circ)
                .with_message("Circular dependency detected".to_string()),
        );
        let mut stamped = 0usize;
        for &vertex_id in cycle {
            if let Some(filter) = dirty_filter
                && !filter.contains(&vertex_id)
            {
                continue;
            }
            self.stamp_cycle_error(vertex_id, &circ_error, delta.as_deref_mut());
            stamped += 1;
        }
        stamped
    }

    /// Stamp a vertex with `#CIRC!` as part of cycle handling.
    ///
    /// Unlike a bare `update_vertex_value`, this first tears down any spill the
    /// vertex previously anchored: it clears the spilled cells, releases the graph
    /// spill registry, drops any lingering region reservation, and mirrors the
    /// cleared cells into the computed overlay — the same teardown a normal scalar/
    /// error result performs (see `apply_non_array_result_from_parallel` /
    /// `clear_spill_projection_and_mirror`). Without this, a #CIRC stamp on a former
    /// spill anchor would leave stale spilled values and a reserved region behind
    /// (issue #111).
    ///
    /// When `delta` is provided, the cleared spill cells are recorded (by
    /// `clear_spill_projection_and_mirror`) and the anchor's own #CIRC change is
    /// recorded here, matching how other result paths emit deltas.
    fn stamp_cycle_error(
        &mut self,
        vertex_id: VertexId,
        circ_error: &LiteralValue,
        mut delta: Option<&mut DeltaCollector>,
    ) {
        // Tear down any previous spill projection/region before overwriting the anchor.
        if self.graph.spill_registry_has_anchor(vertex_id) {
            self.clear_spill_projection_and_mirror(vertex_id, delta.as_deref_mut());
        }
        // Drop any reservation that was never committed (defensive; normally released
        // on the prior successful commit).
        self.spill_mgr.release_owner(vertex_id);

        // Record the anchor's own #CIRC delta, like other result paths.
        if let Some(d) = delta
            && d.mode != DeltaMode::Off
            && let Some(cell) = self.graph.get_cell_ref_for_vertex(vertex_id)
        {
            let sheet_name = self.graph.sheet_name(cell.sheet_id);
            let old = self
                .read_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                .unwrap_or(LiteralValue::Empty);
            if old != *circ_error {
                d.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
            }
        }

        self.graph
            .update_vertex_value(vertex_id, circ_error.clone());
        self.mirror_vertex_value_to_overlay(vertex_id, circ_error);
    }

    /// Dispatch point for one `ScheduleUnit::Cycle` (RFC #112, Stage 2).
    ///
    /// * `CycleDetection::Static` — today's behavior, byte-for-byte: stamp
    ///   `#CIRC!` on the (optionally dirty-filtered) members.
    /// * `CycleDetection::Runtime` — evaluate the SCC via
    ///   [`Self::evaluate_scc_unit`]. The recalc-plan dirty quirk maps to:
    ///   no dirty member → skip the task entirely (values stand); any dirty
    ///   member → the whole SCC evaluates (an SCC cannot be partially
    ///   evaluated).
    ///
    /// Returns the number of `#CIRC!`-stamped vertices, so call sites can
    /// keep their `cycle_errors` accounting (`> 0` ⇒ count the unit).
    fn handle_cycle_unit(
        &mut self,
        cycle: &[VertexId],
        mut delta: Option<&mut DeltaCollector>,
        dirty_filter: Option<&FxHashSet<VertexId>>,
        cancel_flag: Option<&AtomicBool>,
    ) -> Result<usize, ExcelError> {
        match self.config.cycle.detection {
            CycleDetection::Static => {
                Ok(self.apply_cycle_outcome(cycle, delta.as_deref_mut(), dirty_filter))
            }
            CycleDetection::Runtime => {
                if let Some(filter) = dirty_filter
                    && !cycle.iter().any(|v| filter.contains(v))
                {
                    return Ok(0);
                }
                // Both policies share `evaluate_scc_unit`; they differ only
                // in the settle loop's live-cycle arm (Error stamps,
                // Iterate keeps passing — RFC #113).
                self.evaluate_scc_unit(cycle, delta, cancel_flag)
            }
        }
    }

    /// Evaluate one statically-cyclic SCC under `CycleDetection::Runtime`
    /// (design doc `formualizer-stage2-scc-evaluation-design.md` §3; contract
    /// spec §3; Iterate policy arm per RFC #113).
    ///
    /// Phantom SCCs (live-acyclic) produce ordinary values under both
    /// policies; live cycles get `#CIRC!` with live-cycle-only blast radius
    /// under `CyclePolicy::Error`, or Excel-style iterative calculation
    /// (converge per spec §6 or cap at `max_iterations` passes) under
    /// `CyclePolicy::Iterate`. Runs sequentially on the
    /// coordinating thread; commits are write-through per member (no
    /// `ComputedWriteBuffer` — that buffer is scoped to layer evaluation and
    /// always flushed before a Cycle unit runs, G1), so later members' scalar
    /// *and* range reads observe earlier members' results through the overlay
    /// cascade. Deltas are recorded once per member at end of task (G11).
    ///
    /// Returns the number of vertices stamped `#CIRC!`.
    ///
    /// `pub(crate)` so tests can drive SCC shapes (e.g. name-vertex members)
    /// that ingest-time cycle rejection makes unreachable via public edits.
    pub(crate) fn evaluate_scc_unit(
        &mut self,
        cycle: &[VertexId],
        mut delta: Option<&mut DeltaCollector>,
        cancel_flag: Option<&AtomicBool>,
    ) -> Result<usize, ExcelError> {
        struct SccMember {
            vertex: VertexId,
            cell: Option<CellRef>,
        }

        let task_start = crate::instant::FzInstant::now();

        // ── 0. Member order (spec §7.13): cells ascending (sheet, row, col);
        // name vertices after, lexicographic by folded canonical name; any
        // other vertex kind (defensive — `get_evaluation_vertices` only emits
        // formula/name kinds) last by id, never evaluated.
        let mut cell_members: Vec<(VertexId, CellRef)> = Vec::new();
        let mut name_members: Vec<(VertexId, String)> = Vec::new();
        let mut other_members: Vec<VertexId> = Vec::new();
        for &v in cycle {
            match self.graph.get_vertex_kind(v) {
                VertexKind::FormulaScalar | VertexKind::FormulaArray => {
                    match self.graph.get_cell_ref(v) {
                        Some(cell) => cell_members.push((v, cell)),
                        None => other_members.push(v),
                    }
                }
                VertexKind::NamedScalar | VertexKind::NamedArray => {
                    match self.graph.name_key_for_vertex(v) {
                        Some(key) => name_members.push((v, key)),
                        None => other_members.push(v),
                    }
                }
                _ => other_members.push(v),
            }
        }
        cell_members.sort_unstable_by_key(|(_, c)| (c.sheet_id, c.coord.row(), c.coord.col()));
        name_members.sort_unstable_by(|(av, ak), (bv, bk)| ak.cmp(bk).then(av.cmp(bv)));
        other_members.sort_unstable();

        let cell_refs: Vec<CellRef> = cell_members.iter().map(|(_, c)| *c).collect();
        let name_keys: Vec<String> = name_members.iter().map(|(_, k)| k.clone()).collect();
        let mut members: Vec<SccMember> = Vec::with_capacity(cycle.len());
        for (v, c) in &cell_members {
            members.push(SccMember {
                vertex: *v,
                cell: Some(*c),
            });
        }
        for (v, _) in &name_members {
            members.push(SccMember {
                vertex: *v,
                cell: None,
            });
        }
        for v in &other_members {
            members.push(SccMember {
                vertex: *v,
                cell: None,
            });
        }
        let n = members.len();
        // Indices addressable by the collector (cells + names); `other`
        // members can be neither edge sources nor targets.
        let recordable = cell_refs.len() + name_keys.len();

        let circ_error = LiteralValue::Error(
            ExcelError::new(ExcelErrorKind::Circ)
                .with_message("Circular dependency detected".to_string()),
        );

        // ── 0b. Spec-§4 persistence repair: structural edits clear computed
        // overlays wholesale (`clear_computed_overlay_after_row/_col`), but
        // an iterating member's committed value is cycle STATE, not a
        // recomputable cache — and in canonical mode the overlay is its ONLY
        // home. If the overlay entry vanished since the last recalc, re-seed
        // it from the end-of-recalc snapshot (`iterative_state_values`) so
        // pass-1 reads (scalar AND range, via the overlay cascade) observe
        // the persisted value instead of silently restarting at Empty→0.
        // (Found by the iterate edge corpus: inserting/deleting an unrelated
        // row reset accumulators, violating spec §4/§7.15.)
        if !self.iterative_state_values.is_empty() {
            let restore: Vec<(VertexId, LiteralValue)> = members
                .iter()
                .filter_map(|m| {
                    let cell = m.cell?;
                    let persisted = self.iterative_state_values.get(&m.vertex)?;
                    let sheet_name = self.graph.sheet_name(cell.sheet_id);
                    let overlay = self
                        .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                        .unwrap_or(LiteralValue::Empty);
                    if matches!(overlay, LiteralValue::Empty) {
                        Some((m.vertex, persisted.clone()))
                    } else {
                        None
                    }
                })
                .collect();
            for (vertex, value) in restore {
                self.mirror_vertex_value_to_overlay(vertex, &value);
            }
        }

        // ── 1. Pre-task value snapshot (overlay-first for cells — G3; the
        // graph value map may be evicted in value-cache-disabled mode).
        let snapshot: Vec<LiteralValue> = members
            .iter()
            .map(|m| match m.cell {
                Some(cell) => {
                    let sheet_name = self.graph.sheet_name(cell.sheet_id);
                    self.get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                        .unwrap_or(LiteralValue::Empty)
                }
                None => self
                    .graph
                    .get_value(m.vertex)
                    .unwrap_or(LiteralValue::Empty),
            })
            .collect();

        // ── 2. Pre-scan: spill anchors (FormulaArray) are stamped `#CIRC!`
        // with full spill teardown (spec §7.9, #115) and excluded from
        // evaluation. They stay recordable edge TARGETS (readers see `#CIRC!`
        // and propagate). Non-evaluable defensive members are excluded too.
        let mut excluded = vec![false; n];
        let mut last_value = snapshot.clone();
        let mut stamped = 0usize;
        for (i, m) in members.iter().enumerate() {
            match self.graph.get_vertex_kind(m.vertex) {
                VertexKind::FormulaArray => {
                    // Deltas for the cleared spill-region cells (non-members)
                    // can only be recorded here; the anchor's own delta is
                    // covered by the end-of-task snapshot comparison (dedup).
                    self.stamp_cycle_error(m.vertex, &circ_error, delta.as_deref_mut());
                    excluded[i] = true;
                    last_value[i] = circ_error.clone();
                    stamped += 1;
                }
                VertexKind::FormulaScalar | VertexKind::NamedScalar | VertexKind::NamedArray => {}
                _ => excluded[i] = true,
            }
        }

        let collector = LiveEdgeCollector::new_with_names(&cell_refs, &name_keys);

        // Per-member live out-edges, refreshed whenever a member re-runs.
        let mut out_edges: Vec<Vec<u32>> = vec![Vec::new(); n];
        // Position of each member in the most recent pass (-1 = did not run).
        let mut pos: Vec<i64> = vec![-1; n];
        // Whether each member's committed value changed in the most recent pass.
        let mut changed = vec![false; n];

        // Evaluate-and-commit one member; returns Ok(true) when the member was
        // stamped `#CIRC!` (array result — would-be spill anchor, spec §7.9).
        macro_rules! run_member {
            ($i:expr) => {{
                let i: usize = $i;
                let m = &members[i];
                if i < recordable {
                    collector.set_current(i as u32);
                }
                let value = {
                    let ctx = RecordingContext::new(&*self, &collector);
                    match self.evaluate_vertex_recorded(m.vertex, &ctx, &collector) {
                        Ok(v) => v,
                        Err(e) => LiteralValue::Error(e),
                    }
                };
                let is_cell_formula = m.cell.is_some();
                if is_cell_formula && matches!(value, LiteralValue::Array(_)) {
                    // A member that *would* spill inside an SCC gets the
                    // conservative §7.9 verdict. It has never spilled before
                    // (a prior spill would make it FormulaArray, pre-stamped
                    // above), so there is no projection to tear down.
                    self.stamp_cycle_error(m.vertex, &circ_error, None);
                    excluded[i] = true;
                    stamped += 1;
                    changed[i] = last_value[i] != circ_error;
                    last_value[i] = circ_error.clone();
                } else {
                    self.graph.update_vertex_value(m.vertex, value.clone());
                    self.mirror_vertex_value_to_overlay(m.vertex, &value);
                    // §7.14 invariant (G2): a formula member must never be
                    // shadowed by a user/delta overlay entry, or iteration
                    // reads would silently diverge from committed values.
                    #[cfg(debug_assertions)]
                    if let Some(cell) = m.cell {
                        let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                        debug_assert!(
                            self.read_delta_overlay_cell(
                                &sheet_name,
                                cell.coord.row() + 1,
                                cell.coord.col() + 1
                            )
                            .is_none(),
                            "user overlay must never shadow a formula SCC member ({sheet_name}!r{}c{})",
                            cell.coord.row() + 1,
                            cell.coord.col() + 1
                        );
                    }
                    changed[i] = last_value[i] != value;
                    last_value[i] = value;
                }
            }};
        }

        let check_cancel = |flag: Option<&AtomicBool>| -> Result<(), ExcelError> {
            if let Some(flag) = flag
                && flag.load(Ordering::Relaxed)
            {
                return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                    .with_message("Evaluation cancelled during SCC evaluation".to_string()));
            }
            Ok(())
        };

        // ── 3. Pass 1: all evaluable members in member order.
        check_cancel(cancel_flag)?;
        let mut passes = 1usize;
        {
            let mut p = 0i64;
            for i in 0..n {
                if excluded[i] {
                    continue;
                }
                run_member!(i);
                pos[i] = p;
                p += 1;
            }
        }

        // ── 4. Settle loop (design doc §3 step 4; RFC #113 policy arm).
        //
        // Acyclic classifications settle stale readers exactly (identical
        // under both policies — phantom SCCs never iterate). A witnessed
        // live cycle dispatches on policy: `Error` stamps `#CIRC!` and
        // stops; `Iterate` keeps running full passes over all members in
        // member order until converged (spec §6) or capped at
        // `max_iterations` total passes. A live cycle that only appears
        // mid-settle takes the same arm, and a cycle that dissolves
        // mid-iteration falls back to exact acyclic settling.
        //
        // Defensive acyclic budget: the acyclic settle is monotone, so more
        // than |SCC| + 2 settle passes can only be a bug; cap hits stamp the
        // remainder and set telemetry. Tracked via `settle_passes` so
        // iteration passes (legitimately many) don't consume the budget.
        let policy = self.config.cycle.policy;
        let cap = n + 2;
        let mut witnessed_cycles = 0usize;
        let mut capped = false;
        // ── Iterate-policy state ──
        let mut iterating = false;
        let mut converged = false;
        // Values committed by the last *full* pass; `None` until the first
        // iteration pass runs (pass 1 has no predecessor to compare against)
        // and reset when a settle pass runs (no cross-kind comparisons).
        let mut prev_pass: Option<Vec<LiteralValue>> = None;
        // Final-round convergence stats (overwritten per round so the values
        // reported are the ones observed at stop).
        let mut iter_max_delta = 0f64;
        let mut iter_nan_converged = 0usize;
        // Acyclic stale-reader re-eval passes (defensive budget; under pure
        // Error flow `1 + settle_passes == passes`, preserving Stage-2
        // behavior exactly).
        let mut settle_passes = 0usize;
        loop {
            // Drain this pass's recordings; members that ran replace their
            // out-edge set, members that didn't keep last-known edges.
            let drained = collector.take_edges();
            for i in 0..n {
                if pos[i] >= 0 {
                    out_edges[i].clear();
                }
            }
            for (from, to) in drained {
                debug_assert!(
                    pos[from as usize] >= 0,
                    "edge from a member that did not run"
                );
                out_edges[from as usize].push(to);
            }
            let mut edges: Vec<(u32, u32)> = Vec::new();
            for (i, outs) in out_edges.iter().enumerate() {
                if excluded[i] {
                    continue;
                }
                for &t in outs {
                    edges.push((i as u32, t));
                }
            }
            edges.sort_unstable();
            edges.dedup();

            let analysis = analyze_live_graph(n, &edges);

            if analysis.cycle_count > 0 {
                // Classification repeats every iteration pass under
                // `Iterate`; record the widest single witness instead of
                // accumulating so the count stays "distinct live cycles".
                witnessed_cycles = witnessed_cycles.max(analysis.cycle_count);
                match policy {
                    CyclePolicy::Error => {
                        // POLICY (Error): stamp every member of a live cycle,
                        // then one settling pass over the remaining members in
                        // live-topological order so error propagation
                        // downstream is consistent (spec §3.4). Blast radius =
                        // live cycles only.
                        for i in 0..n {
                            if analysis.in_cycle[i] && !excluded[i] {
                                self.stamp_cycle_error(members[i].vertex, &circ_error, None);
                                excluded[i] = true;
                                last_value[i] = circ_error.clone();
                                stamped += 1;
                            }
                        }
                        check_cancel(cancel_flag)?;
                        let order: Vec<usize> = analysis
                            .topo
                            .iter()
                            .map(|&i| i as usize)
                            .filter(|&i| !excluded[i])
                            .collect();
                        if !order.is_empty() {
                            passes += 1;
                            for i in order {
                                run_member!(i);
                            }
                        }
                        break;
                    }
                    CyclePolicy::Iterate {
                        max_iterations,
                        max_change,
                    } => {
                        // POLICY (Iterate), spec §3.5/§6.
                        iterating = true;

                        // Convergence test: the full pass that just completed
                        // vs the previous full pass, per the spec-§6 rules.
                        // `prev_pass` is `None` until an iteration pass has
                        // run — pass 1 has no predecessor, so no convergence
                        // test occurs before the second pass (spec §6).
                        if let Some(prev) = &prev_pass {
                            let mut round_max_delta = 0f64;
                            let mut round_nan = 0usize;
                            let mut all_converged = true;
                            for i in 0..n {
                                if excluded[i] {
                                    // Stamped mid-iteration (array result,
                                    // §7.9): the value is pinned and cannot
                                    // change again — trivially settled.
                                    continue;
                                }
                                let out = crate::engine::convergence::values_converged(
                                    &prev[i],
                                    &last_value[i],
                                    max_change,
                                    self.config.date_system,
                                );
                                if out.nan_converged {
                                    round_nan += 1;
                                }
                                if let Some(d) = out.abs_delta {
                                    round_max_delta = round_max_delta.max(d);
                                }
                                if !out.converged {
                                    all_converged = false;
                                }
                            }
                            // Overwrite (not max): telemetry reports the
                            // round observed at stop.
                            iter_max_delta = round_max_delta;
                            iter_nan_converged = round_nan;
                            if all_converged {
                                converged = true;
                                break;
                            }
                        }

                        // ── Pass-counting reconciliation (spec §6/§7.6):
                        // `max_iterations` counts TOTAL passes, pass 1
                        // included, and pass 1 has already run by the time a
                        // live cycle is first witnessed here. The budget is
                        // therefore checked BEFORE evaluating anything more:
                        // with `max_iterations: 1` we stop right here — each
                        // member was evaluated exactly once this recalc (the
                        // Excel accumulator contract) and no convergence test
                        // ran (`prev_pass` is still `None`). Capping keeps
                        // the last committed values and is NOT an error
                        // (Excel parity); telemetry records it.
                        if passes >= max_iterations as usize {
                            capped = true;
                            break;
                        }

                        check_cancel(cancel_flag)?;
                        // One more full pass over every evaluable member in
                        // member order (Gauss–Seidel: each commit is visible
                        // to later members within the pass). Live edges
                        // re-record — guards can flip near convergence
                        // (§7.3) — so classification repeats next time
                        // around, and a cycle that dissolves drops back to
                        // the exact acyclic settle below.
                        prev_pass = Some(last_value.clone());
                        for x in pos.iter_mut() {
                            *x = -1;
                        }
                        changed.fill(false);
                        passes += 1;
                        let mut p = 0i64;
                        for i in 0..n {
                            if excluded[i] {
                                continue;
                            }
                            run_member!(i);
                            pos[i] = p;
                            p += 1;
                        }
                        continue;
                    }
                }
            }

            // Acyclic: find stale readers — members whose live read of `to`
            // happened before `to`'s value changed in the pass that just ran.
            let mut stale: Vec<usize> = Vec::new();
            for i in 0..n {
                if excluded[i] {
                    continue;
                }
                let is_stale = out_edges[i].iter().any(|&t| {
                    let t = t as usize;
                    changed[t] && (pos[i] < 0 || (pos[t] >= 0 && pos[i] < pos[t]))
                });
                if is_stale {
                    stale.push(i);
                }
            }
            if stale.is_empty() {
                break; // values exact — phantom SCC (or dissolved live cycle)
            }
            if 1 + settle_passes >= cap {
                // Defensive only; hitting this is a bug (loud telemetry).
                capped = true;
                for (i, m) in members.iter().enumerate() {
                    if !excluded[i] {
                        self.stamp_cycle_error(m.vertex, &circ_error, None);
                        excluded[i] = true;
                        last_value[i] = circ_error.clone();
                        stamped += 1;
                    }
                }
                break;
            }

            check_cancel(cancel_flag)?;
            // Re-evaluate stale readers in live-topo order, recording fresh
            // edges (branches may flip on re-eval — spec §7.3 — which is why
            // classification repeats).
            // A settle pass is a partial sweep: drop the full-pass baseline
            // so a live cycle (re)appearing afterwards never compares values
            // across mixed pass kinds.
            prev_pass = None;
            let topo_pos = analysis.topo_positions();
            stale.sort_unstable_by_key(|&i| topo_pos[i]);
            for x in pos.iter_mut() {
                *x = -1;
            }
            changed.fill(false);
            passes += 1;
            settle_passes += 1;
            for (p, i) in stale.into_iter().enumerate() {
                run_member!(i);
                pos[i] = p as i64;
            }
        }

        // Iteration that ended because the live cycle dissolved and the
        // acyclic settle reached exactness counts as converged (values are
        // exact, strictly better than threshold-converged). The defensive
        // settle cap (`capped` + stamping) is not.
        if iterating && !converged && !capped {
            converged = true;
        }

        // ── 5. End of task: one delta per member whose final value differs
        // from the pre-task snapshot (spec §3 side-effect rule, G11).
        collector.clear_current();
        if let Some(d) = delta
            && d.mode != DeltaMode::Off
        {
            for (i, m) in members.iter().enumerate() {
                if let Some(cell) = m.cell
                    && last_value[i] != snapshot[i]
                {
                    d.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                }
            }
        }

        // Members of an SCC that iterated re-evaluate on EVERY recalc, like
        // Excel's circular cells: register them for the end-of-recalc
        // volatile-like redirty (see `pending_iterative_redirty`). Marking
        // any one member propagates around the (strongly connected) SCC and
        // to downstream dependents, but all members are registered so the
        // contract survives partial structural edits between recalcs.
        if iterating {
            self.pending_iterative_redirty
                .extend(members.iter().map(|m| m.vertex));
        }

        {
            let t = &mut self.last_cycle_telemetry;
            t.static_sccs += 1;
            if witnessed_cycles == 0 && stamped == 0 && !capped {
                t.phantom_sccs += 1;
            }
            t.live_cycles_witnessed += witnessed_cycles;
            t.circ_cells_stamped += stamped;
            t.settle_passes_total += passes;
            t.max_passes_single_scc = t.max_passes_single_scc.max(passes);
            if iterating {
                t.iterated_sccs += 1;
                if converged {
                    t.converged_sccs += 1;
                }
                t.max_abs_delta_at_stop = t.max_abs_delta_at_stop.max(iter_max_delta);
                t.nan_converged += iter_nan_converged;
            }
            if capped {
                t.capped_sccs += 1;
            }
            t.elapsed_ms += task_start.elapsed().as_millis();
        }

        Ok(stamped)
    }

    /// Recorded sibling of [`Self::evaluate_vertex_immutable`]: evaluates one
    /// SCC member's AST via an [`Interpreter`] over a [`RecordingContext`] so
    /// reads that actually occur are captured as live edges. Value semantics
    /// must match `evaluate_vertex_immutable` exactly (including the missing-
    /// AST `Number(0.0)` quirk, G14); named Cell/Range/Literal definitions
    /// delegate to it after recording the definition region by hand (those
    /// reads bypass the context).
    fn evaluate_vertex_recorded(
        &self,
        vertex_id: VertexId,
        ctx: &RecordingContext<'_, R>,
        collector: &LiveEdgeCollector,
    ) -> Result<LiteralValue, ExcelError> {
        if !self.graph.vertex_exists(vertex_id) {
            return Err(ExcelError::new(formualizer_common::ExcelErrorKind::Ref)
                .with_message(format!("Vertex not found: {vertex_id:?}")));
        }

        let kind = self.graph.get_vertex_kind(vertex_id);
        let sheet_id = self.graph.get_vertex_sheet_id(vertex_id);

        match kind {
            VertexKind::FormulaScalar | VertexKind::FormulaArray => {
                let Some(ast_id) = self.graph.get_formula_id(vertex_id) else {
                    return Ok(LiteralValue::Number(0.0)); // G14 quirk
                };
                let sheet_name = self.graph.sheet_name(sheet_id);
                let cell_ref = self
                    .graph
                    .get_cell_ref(vertex_id)
                    .expect("cell ref for vertex");
                let interpreter = Interpreter::new_with_cell(ctx, sheet_name, cell_ref);
                interpreter
                    .evaluate_arena_ast(ast_id, self.graph.data_store(), self.graph.sheet_reg())
                    .map(|cv| cv.into_literal())
            }
            VertexKind::NamedScalar | VertexKind::NamedArray => {
                let named_range = self.graph.named_range_by_vertex(vertex_id).ok_or_else(|| {
                    ExcelError::new(ExcelErrorKind::Name)
                        .with_message("Named range metadata missing".to_string())
                })?;

                match &named_range.definition {
                    NamedDefinition::Formula { ast, .. } => {
                        let context_sheet = match named_range.scope {
                            NameScope::Sheet(id) => id,
                            NameScope::Workbook => sheet_id,
                        };
                        let sheet_name = self.graph.sheet_name(context_sheet);
                        let cell_ref = self
                            .graph
                            .get_cell_ref(vertex_id)
                            .unwrap_or_else(|| self.graph.make_cell_ref(sheet_name, 0, 0));
                        let interpreter = Interpreter::new_with_cell(ctx, sheet_name, cell_ref);
                        if kind == VertexKind::NamedScalar {
                            interpreter.evaluate_ast(ast).map(|cv| cv.into_literal())
                        } else {
                            match interpreter.evaluate_ast(ast) {
                                Ok(cv) => match cv.into_literal() {
                                    v @ LiteralValue::Array(_) => Ok(v),
                                    other => Ok(LiteralValue::Array(vec![vec![other]])),
                                },
                                Err(err) => Ok(LiteralValue::Error(err)),
                            }
                        }
                    }
                    NamedDefinition::Cell(cell_ref) => {
                        // The definition is read via direct grid access in
                        // `evaluate_vertex_immutable`; record the live edge
                        // by hand before delegating.
                        collector.record_scalar(
                            cell_ref.sheet_id,
                            cell_ref.coord.row(),
                            cell_ref.coord.col(),
                        );
                        self.evaluate_vertex_immutable(vertex_id)
                    }
                    NamedDefinition::Range(range_ref) => {
                        if range_ref.start.sheet_id == range_ref.end.sheet_id {
                            collector.record_rect(
                                range_ref.start.sheet_id,
                                range_ref.start.coord.row(),
                                range_ref.start.coord.col(),
                                range_ref.end.coord.row(),
                                range_ref.end.coord.col(),
                            );
                        }
                        self.evaluate_vertex_immutable(vertex_id)
                    }
                    NamedDefinition::Literal(_) => self.evaluate_vertex_immutable(vertex_id),
                }
            }
            _ => self.evaluate_vertex_immutable(vertex_id),
        }
    }

    /// Helper: commit spill via shim and mirror resulting cells into Arrow overlay when enabled.
    fn commit_spill_and_mirror(
        &mut self,
        anchor_vertex: VertexId,
        targets: &[CellRef],
        rows: Vec<Vec<LiteralValue>>,
        delta: Option<&mut DeltaCollector>,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
    ) -> Result<(), ExcelError> {
        let prev_spill_cells = self
            .graph
            .spill_cells_for_anchor(anchor_vertex)
            .map(|cells| cells.to_vec())
            .unwrap_or_default();

        if let Some(delta) = delta
            && delta.mode != DeltaMode::Off
        {
            let target_set: std::collections::HashSet<CellRef, CoordBuildHasher> =
                targets.iter().copied().collect();
            let empty = LiteralValue::Empty;

            // Clears (prev - targets)
            for cell in prev_spill_cells.iter() {
                if target_set.contains(cell) {
                    continue;
                }
                let sheet_name = self.graph.sheet_name(cell.sheet_id);
                let old = self
                    .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                    .unwrap_or(LiteralValue::Empty);
                if old != empty {
                    delta.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                }
            }

            // Writes (targets)
            if !targets.is_empty() && !rows.is_empty() && !rows[0].is_empty() {
                let width = rows[0].len();
                for (idx, cell) in targets.iter().enumerate() {
                    let r_off = idx / width;
                    let c_off = idx % width;
                    let new = rows
                        .get(r_off)
                        .and_then(|r| r.get(c_off))
                        .cloned()
                        .unwrap_or(LiteralValue::Empty);
                    let sheet_name = self.graph.sheet_name(cell.sheet_id);
                    let old = self
                        .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                        .unwrap_or(LiteralValue::Empty);
                    if old != new {
                        delta.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                    }
                }
            } else {
                // Degenerate shapes: if we have targets but no rows, treat as writing Empty.
                for cell in targets.iter() {
                    let sheet_name = self.graph.sheet_name(cell.sheet_id);
                    let old = self
                        .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                        .unwrap_or(LiteralValue::Empty);
                    if !matches!(old, LiteralValue::Empty) {
                        delta.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                    }
                }
            }
        }

        // Commit via shim (releases locks). When the graph value cache is disabled (Arrow-canonical
        // values), plan/commit must consult Arrow storage to detect non-empty value blockers.
        let arrow_sheets = &self.arrow_sheets;
        self.spill_mgr.commit_array_with_value_probe(
            &mut self.graph,
            anchor_vertex,
            targets,
            rows.clone(),
            overwritable_formulas,
            |g, cell| {
                let sheet_name = g.sheet_name(cell.sheet_id);
                let asheet = arrow_sheets.sheet(sheet_name)?;
                let r0 = cell.coord.row() as usize;
                let c0 = cell.coord.col() as usize;
                let v = asheet.get_cell_value(r0, c0);
                if matches!(v, LiteralValue::Empty) {
                    None
                } else {
                    Some(v)
                }
            },
        )?;

        if let Some(scope) = Self::formula_plane_region_from_cells(&prev_spill_cells) {
            self.record_formula_plane_structural_change(scope);
        }
        if let Some(scope) = Self::formula_plane_region_from_cells(targets) {
            self.record_formula_plane_structural_change(scope);
        }

        if self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled
        {
            if !prev_spill_cells.is_empty() {
                let target_set: std::collections::HashSet<CellRef, CoordBuildHasher> =
                    targets.iter().copied().collect();
                let empty = LiteralValue::Empty;
                for cell in prev_spill_cells.iter() {
                    if !target_set.contains(cell) {
                        let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                        self.mirror_value_to_computed_overlay(
                            &sheet_name,
                            cell.coord.row() + 1,
                            cell.coord.col() + 1,
                            &empty,
                        );
                    }
                }
            }

            for (idx, cell) in targets.iter().enumerate() {
                if rows.is_empty() || rows[0].is_empty() {
                    break;
                }
                let width = rows[0].len();
                let r_off = idx / width;
                let c_off = idx % width;
                let v = rows[r_off][c_off].clone();
                let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                self.mirror_value_to_computed_overlay(
                    &sheet_name,
                    cell.coord.row() + 1,
                    cell.coord.col() + 1,
                    &v,
                );
            }
        }
        Ok(())
    }
}

// ── Effects pipeline (ticket 603) ──────────────────────────────────────────
//
// Compute → Plan → Apply separation for evaluation side-effects.

use crate::engine::effects::Effect;
use crate::engine::graph::editor::change_log::{ChangeEvent, ChangeLog, SpillSnapshot};

impl<R> Engine<R>
where
    R: EvaluationContext,
{
    /// Plan effects for a single vertex after its value has been computed.
    ///
    /// This reads graph state but only performs lightweight mutations
    /// (`set_kind`, `spill_mgr.reserve`) that are needed for correctness
    /// during the planning phase.  Value-changing mutations are deferred to
    /// `apply_effect`.
    pub(crate) fn plan_vertex_effects(
        &mut self,
        vertex_id: VertexId,
        computed_value: LiteralValue,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
    ) -> Result<Vec<Effect>, ExcelError> {
        let kind = self.graph.get_vertex_kind(vertex_id);
        let is_formula = matches!(kind, VertexKind::FormulaScalar | VertexKind::FormulaArray);

        // If this vertex's cell is currently covered by a spill from a different
        // anchor, ignore the computed result.  Formula vertices are exempt:
        // they must still evaluate so that overlapping spills produce #SPILL!.
        if !is_formula {
            if let Some(cell) = self.graph.get_cell_ref(vertex_id)
                && let Some(owner) = self.graph.spill_registry_anchor_for_cell(cell)
                && owner != vertex_id
            {
                return Ok(Vec::new());
            }
            // Non-formula vertices: store value as-is (arrays remain arrays; no spill).
            return Ok(vec![Effect::WriteCell {
                vertex_id,
                value: computed_value,
            }]);
        }

        match computed_value {
            LiteralValue::Array(rows) => {
                self.plan_array_effects(vertex_id, rows, overwritable_formulas)
            }
            other => self.plan_scalar_effects(vertex_id, other),
        }
    }

    /// Plan effects for a formula vertex that produced a scalar/error result.
    fn plan_scalar_effects(
        &self,
        vertex_id: VertexId,
        value: LiteralValue,
    ) -> Result<Vec<Effect>, ExcelError> {
        let has_spill = self
            .graph
            .spill_cells_for_anchor(vertex_id)
            .is_some_and(|c| !c.is_empty());

        let mut effects = Vec::new();
        if has_spill {
            effects.push(Effect::SpillClear {
                anchor_vertex: vertex_id,
            });
        }
        effects.push(Effect::WriteCell { vertex_id, value });
        Ok(effects)
    }

    /// Plan effects for a formula vertex that produced an array result.
    fn plan_array_effects(
        &mut self,
        vertex_id: VertexId,
        rows: Vec<Vec<LiteralValue>>,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
    ) -> Result<Vec<Effect>, ExcelError> {
        // Lightweight mutation needed for correct spill-blocking checks.
        self.graph.set_kind(vertex_id, VertexKind::FormulaArray);

        let anchor = self
            .graph
            .get_cell_ref(vertex_id)
            .expect("cell ref for vertex");
        let sheet_id = anchor.sheet_id;
        let h = rows.len() as u32;
        let w = rows.first().map(|r| r.len()).unwrap_or(0) as u32;

        // Hard cap to avoid vertex explosion from huge dynamic arrays.
        let spill_cells = (h as u64).saturating_mul(w as u64);
        if spill_cells > self.config.spill.max_spill_cells as u64 {
            return self.plan_spill_error_effects(vertex_id, "SpillTooLarge", h, w);
        }

        // Bounds check to avoid out-of-range writes (align to AbsCoord capacity).
        const PACKED_MAX_ROW: u32 = 1_048_575;
        const PACKED_MAX_COL: u32 = 16_383;
        let end_row = anchor.coord.row().saturating_add(h).saturating_sub(1);
        let end_col = anchor.coord.col().saturating_add(w).saturating_sub(1);
        if end_row > PACKED_MAX_ROW || end_col > PACKED_MAX_COL {
            return self.plan_spill_error_effects(vertex_id, "Spill exceeds sheet bounds", h, w);
        }

        let mut targets = Vec::new();
        for r in 0..h {
            for c in 0..w {
                targets.push(self.graph.make_cell_ref_internal(
                    sheet_id,
                    anchor.coord.row() + r,
                    anchor.coord.col() + c,
                ));
            }
        }

        // Region lock via spill manager.
        match self.spill_mgr.reserve(
            vertex_id,
            anchor,
            SpillShape { rows: h, cols: w },
            SpillMeta {
                epoch: self.recalc_epoch,
                config: self.config.spill,
            },
        ) {
            Ok(()) => {
                // Validate spill region is available.
                if let Err(_e) = self.graph.plan_spill_region_allowing_formula_overwrite(
                    vertex_id,
                    &targets,
                    overwritable_formulas,
                ) {
                    return self.plan_spill_error_effects(vertex_id, "Spill blocked", h, w);
                }

                // Arrow-canonical mode: graph planning cannot see non-empty value blockers because
                // cell values are not cached in the dependency graph. Consult Arrow storage to
                // detect occupied cells in the target region.
                if !self.graph.value_cache_enabled() {
                    let sheet_name = self.graph.sheet_name(sheet_id);
                    if let Some(asheet) = self.sheet_store().sheet(sheet_name) {
                        for cell in targets.iter() {
                            // Allow overwriting the anchor itself.
                            if *cell == anchor {
                                continue;
                            }
                            // Allow cells already owned by a spill (plan() validated spill ownership).
                            if self.graph.spill_registry_anchor_for_cell(*cell).is_some() {
                                continue;
                            }
                            // Skip formula blockers; plan() handled them (or allowed).
                            if let Some(&vid) = self.graph.get_vertex_id_for_address(cell)
                                && vid != vertex_id
                            {
                                match self.graph.get_vertex_kind(vid) {
                                    VertexKind::FormulaScalar | VertexKind::FormulaArray => {
                                        continue;
                                    }
                                    _ => {}
                                }
                            }

                            let v = asheet.get_cell_value(
                                cell.coord.row() as usize,
                                cell.coord.col() as usize,
                            );
                            if !matches!(v, LiteralValue::Empty) {
                                return self.plan_spill_error_effects(
                                    vertex_id,
                                    "BlockedByValue",
                                    h,
                                    w,
                                );
                            }
                        }
                    }
                }

                let top_left = rows
                    .first()
                    .and_then(|r| r.first())
                    .cloned()
                    .unwrap_or(LiteralValue::Empty);

                let mut effects = Vec::new();
                // Clear previous spill if any.
                let has_prev = self
                    .graph
                    .spill_cells_for_anchor(vertex_id)
                    .is_some_and(|c| !c.is_empty());
                if has_prev {
                    effects.push(Effect::SpillClear {
                        anchor_vertex: vertex_id,
                    });
                }
                effects.push(Effect::SpillCommit {
                    anchor_vertex: vertex_id,
                    anchor_cell: anchor,
                    target_cells: targets,
                    values: rows,
                });
                effects.push(Effect::WriteCell {
                    vertex_id,
                    value: top_left,
                });
                Ok(effects)
            }
            Err(e) => {
                let msg = e.message.unwrap_or_else(|| "Spill blocked".to_string());
                self.plan_spill_error_effects(vertex_id, &msg, h, w)
            }
        }
    }

    /// Build the effect list for a spill that failed validation.
    fn plan_spill_error_effects(
        &self,
        vertex_id: VertexId,
        message: &str,
        expected_rows: u32,
        expected_cols: u32,
    ) -> Result<Vec<Effect>, ExcelError> {
        let spill_err = ExcelError::new(ExcelErrorKind::Spill)
            .with_message(message)
            .with_extra(formualizer_common::ExcelErrorExtra::Spill {
                expected_rows,
                expected_cols,
            });
        let spill_val = LiteralValue::Error(spill_err);

        let effects = vec![
            Effect::SpillClear {
                anchor_vertex: vertex_id,
            },
            Effect::WriteCell {
                vertex_id,
                value: spill_val,
            },
        ];
        Ok(effects)
    }

    /// Apply a single effect, performing the actual graph mutations.
    pub(crate) fn apply_effect(
        &mut self,
        effect: &Effect,
        delta: Option<&mut DeltaCollector>,
        log: Option<&mut ChangeLog>,
    ) -> Result<(), ExcelError> {
        self.apply_effect_with_computed_writes(effect, delta, log, None)
    }

    fn apply_effect_with_computed_writes(
        &mut self,
        effect: &Effect,
        delta: Option<&mut DeltaCollector>,
        log: Option<&mut ChangeLog>,
        computed_writes: Option<&mut ComputedWriteBuffer>,
    ) -> Result<(), ExcelError> {
        match effect {
            Effect::WriteCell { vertex_id, value } => {
                self.apply_write_cell(*vertex_id, value, delta, computed_writes)?;
            }
            Effect::SpillClear { anchor_vertex } => {
                self.apply_spill_clear(*anchor_vertex, delta, log, computed_writes)?;
            }
            Effect::SpillCommit {
                anchor_vertex,
                anchor_cell: _,
                target_cells,
                values,
            } => {
                self.apply_spill_commit(
                    *anchor_vertex,
                    target_cells,
                    values.clone(),
                    delta,
                    log,
                    computed_writes,
                )?;
            }
        }
        Ok(())
    }

    /// Apply a WriteCell effect.
    fn apply_write_cell(
        &mut self,
        vertex_id: VertexId,
        value: &LiteralValue,
        delta: Option<&mut DeltaCollector>,
        mut computed_writes: Option<&mut ComputedWriteBuffer>,
    ) -> Result<(), ExcelError> {
        if let Some(d) = delta
            && d.mode != DeltaMode::Off
        {
            if let Some(buffer) = computed_writes.as_deref_mut() {
                self.flush_computed_write_buffer(buffer)?;
            }
            if let Some(cell) = self.graph.get_cell_ref_for_vertex(vertex_id) {
                let sheet_name = self.graph.sheet_name(cell.sheet_id);
                let old = self
                    .read_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                    .unwrap_or(LiteralValue::Empty);
                if old != *value {
                    d.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                }
            }
        }
        self.graph.update_vertex_value(vertex_id, value.clone());
        self.record_vertex_value_to_overlay(vertex_id, value, computed_writes)?;
        Ok(())
    }

    /// Apply a SpillClear effect.
    fn apply_spill_clear(
        &mut self,
        anchor_vertex: VertexId,
        delta: Option<&mut DeltaCollector>,
        log: Option<&mut ChangeLog>,
        computed_writes: Option<&mut ComputedWriteBuffer>,
    ) -> Result<(), ExcelError> {
        if let Some(buffer) = computed_writes {
            self.flush_computed_write_buffer(buffer)?;
        }

        let spill_cells = self
            .graph
            .spill_cells_for_anchor(anchor_vertex)
            .map(|cells| cells.to_vec())
            .unwrap_or_default();
        if spill_cells.is_empty() {
            return Ok(());
        }

        // Snapshot for ChangeLog before clearing.
        let snapshot = if log.is_some() {
            self.snapshot_spill_for_anchor(anchor_vertex)
        } else {
            None
        };

        // Record delta for cleared cells.
        if let Some(d) = delta
            && d.mode != DeltaMode::Off
        {
            let empty = LiteralValue::Empty;
            for cell in spill_cells.iter() {
                let sheet_name = self.graph.sheet_name(cell.sheet_id);
                let old = self
                    .get_cell_value(sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                    .unwrap_or(LiteralValue::Empty);
                if old != empty {
                    d.record_cell(cell.sheet_id, cell.coord.row(), cell.coord.col());
                }
            }
        }

        self.graph.clear_spill_region(anchor_vertex);
        if let Some(scope) = Self::formula_plane_region_from_cells(&spill_cells) {
            self.record_formula_plane_structural_change(scope);
        }

        // Mirror Empty to Arrow overlay for cleared cells.
        if self.config.arrow_storage_enabled
            && self.config.delta_overlay_enabled
            && self.config.write_formula_overlay_enabled
        {
            let empty = LiteralValue::Empty;
            for cell in spill_cells.iter() {
                let sheet_name = self.graph.sheet_name(cell.sheet_id).to_string();
                self.mirror_value_to_computed_overlay(
                    &sheet_name,
                    cell.coord.row() + 1,
                    cell.coord.col() + 1,
                    &empty,
                );
            }
        }

        // ChangeLog.
        if let Some(log) = log
            && let Some(old) = snapshot
        {
            log.record(ChangeEvent::SpillCleared {
                anchor: anchor_vertex,
                old,
            });
        }
        Ok(())
    }

    /// Apply a SpillCommit effect.
    fn apply_spill_commit(
        &mut self,
        anchor_vertex: VertexId,
        target_cells: &[CellRef],
        values: Vec<Vec<LiteralValue>>,
        delta: Option<&mut DeltaCollector>,
        log: Option<&mut ChangeLog>,
        computed_writes: Option<&mut ComputedWriteBuffer>,
    ) -> Result<(), ExcelError> {
        if let Some(buffer) = computed_writes {
            self.flush_computed_write_buffer(buffer)?;
        }

        // Snapshot for ChangeLog before commit.
        let old_snapshot = if log.is_some() {
            self.snapshot_spill_for_anchor(anchor_vertex)
        } else {
            None
        };

        // Delegate to existing commit_spill_and_mirror for delta + overlay logic.
        self.commit_spill_and_mirror(
            anchor_vertex,
            target_cells,
            values.clone(),
            delta,
            None, // overwritable_formulas already validated in plan phase
        )?;

        // ChangeLog.
        if let Some(log) = log {
            log.record(ChangeEvent::SpillCommitted {
                anchor: anchor_vertex,
                old: old_snapshot,
                new: SpillSnapshot {
                    target_cells: target_cells.to_vec(),
                    values,
                },
            });
        }
        Ok(())
    }

    /// Snapshot a spill region for ChangeLog recording.
    ///
    /// Extracted from `VertexEditor::snapshot_spill_for_anchor` to be usable
    /// without creating a `VertexEditor`.
    fn snapshot_spill_for_anchor(&self, anchor: VertexId) -> Option<SpillSnapshot> {
        let cells = self.graph.spill_cells_for_anchor(anchor)?.to_vec();
        if cells.is_empty() {
            return None;
        }

        let max = self.config.spill.max_spill_cells as usize;
        let mut cells = cells;
        if cells.len() > max {
            cells.truncate(max);
        }

        let first = *cells.first().expect("non-empty spill cells");
        let sheet_name = self.graph.sheet_name(first.sheet_id).to_string();
        let row0 = first.coord.row();
        let col0 = first.coord.col();

        let mut max_row = row0;
        let mut max_col = col0;
        let mut by_coord: FxHashMap<(u32, u32), LiteralValue> = FxHashMap::default();
        for cell in &cells {
            max_row = max_row.max(cell.coord.row());
            max_col = max_col.max(cell.coord.col());
            let v = self
                .get_cell_value(&sheet_name, cell.coord.row() + 1, cell.coord.col() + 1)
                .unwrap_or(LiteralValue::Empty);
            by_coord.insert((cell.coord.row(), cell.coord.col()), v);
        }

        let rows = (max_row - row0 + 1) as usize;
        let cols = (max_col - col0 + 1) as usize;
        let mut values: Vec<Vec<LiteralValue>> = Vec::with_capacity(rows);
        for r in 0..rows {
            let mut row: Vec<LiteralValue> = Vec::with_capacity(cols);
            for c in 0..cols {
                row.push(
                    by_coord
                        .get(&(row0 + r as u32, col0 + c as u32))
                        .cloned()
                        .unwrap_or(LiteralValue::Empty),
                );
            }
            values.push(row);
        }

        Some(SpillSnapshot {
            target_cells: cells,
            values,
        })
    }

    fn flush_before_range_dependent_vertex(
        &mut self,
        vertex_id: VertexId,
        computed_writes: &mut ComputedWriteBuffer,
    ) -> Result<(), ExcelError> {
        if self.graph.get_range_dependencies(vertex_id).is_some() {
            self.flush_computed_write_buffer(computed_writes)?;
        }
        Ok(())
    }

    fn plan_vertex_effects_with_computed_flush(
        &mut self,
        vertex_id: VertexId,
        computed_value: LiteralValue,
        overwritable_formulas: Option<&rustc_hash::FxHashSet<VertexId>>,
        computed_writes: &mut ComputedWriteBuffer,
    ) -> Result<Vec<Effect>, ExcelError> {
        if matches!(&computed_value, LiteralValue::Array(_)) {
            self.flush_computed_write_buffer(computed_writes)?;
        }
        self.plan_vertex_effects(vertex_id, computed_value, overwritable_formulas)
    }

    // ── Layer evaluation via effects pipeline ──────────────────────────────

    fn evaluate_small_layer_direct_effects(
        &mut self,
        layer: &super::scheduler::Layer,
        mut delta: Option<&mut DeltaCollector>,
        mut log: Option<&mut ChangeLog>,
        cancel_flag: Option<&AtomicBool>,
        cancel_check_every: usize,
        cancel_message: &'static str,
    ) -> Result<usize, ExcelError> {
        for (i, &vertex_id) in layer.vertices.iter().enumerate() {
            if cancel_check_every > 0
                && i % cancel_check_every == 0
                && cancel_flag.is_some_and(|flag| flag.load(Ordering::Relaxed))
            {
                return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                    .with_message(cancel_message.to_string()));
            }
            let value = match self.evaluate_vertex_immutable(vertex_id) {
                Ok(v) => v,
                Err(e) => LiteralValue::Error(e),
            };
            let effects = self.plan_vertex_effects(vertex_id, value, None)?;
            for effect in &effects {
                self.apply_effect_with_computed_writes(
                    effect,
                    delta.as_deref_mut(),
                    log.as_deref_mut(),
                    None,
                )?;
            }
        }
        Ok(layer.vertices.len())
    }

    /// Evaluate a layer sequentially using the effects pipeline.
    fn evaluate_layer_sequential_effects(
        &mut self,
        layer: &super::scheduler::Layer,
    ) -> Result<usize, ExcelError> {
        if layer.vertices.len() < COMPUTED_WRITE_COALESCING_MIN_LAYER_WIDTH {
            return self.evaluate_small_layer_direct_effects(
                layer,
                None,
                None,
                None,
                0,
                "Evaluation cancelled within layer",
            );
        }

        let mut computed_writes = ComputedWriteBuffer::default();
        for &vertex_id in &layer.vertices {
            self.flush_before_range_dependent_vertex(vertex_id, &mut computed_writes)?;
            let value = match self.evaluate_vertex_immutable(vertex_id) {
                Ok(v) => v,
                Err(e) => LiteralValue::Error(e),
            };
            let effects = match self.plan_vertex_effects_with_computed_flush(
                vertex_id,
                value,
                None,
                &mut computed_writes,
            ) {
                Ok(effects) => effects,
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            };
            for effect in &effects {
                if let Err(e) = self.apply_effect_with_computed_writes(
                    effect,
                    None,
                    None,
                    Some(&mut computed_writes),
                ) {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }
        self.flush_computed_write_buffer(&mut computed_writes)?;
        Ok(layer.vertices.len())
    }

    /// Evaluate a layer sequentially with delta collection via effects pipeline.
    fn evaluate_layer_sequential_with_delta_effects(
        &mut self,
        layer: &super::scheduler::Layer,
        delta: &mut DeltaCollector,
    ) -> Result<usize, ExcelError> {
        if layer.vertices.len() < COMPUTED_WRITE_COALESCING_MIN_LAYER_WIDTH {
            return self.evaluate_small_layer_direct_effects(
                layer,
                Some(delta),
                None,
                None,
                0,
                "Evaluation cancelled within layer",
            );
        }

        let mut computed_writes = ComputedWriteBuffer::default();
        for &vertex_id in &layer.vertices {
            self.flush_before_range_dependent_vertex(vertex_id, &mut computed_writes)?;
            let value = match self.evaluate_vertex_immutable(vertex_id) {
                Ok(v) => v,
                Err(e) => LiteralValue::Error(e),
            };
            let effects = match self.plan_vertex_effects_with_computed_flush(
                vertex_id,
                value,
                None,
                &mut computed_writes,
            ) {
                Ok(effects) => effects,
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            };
            for effect in &effects {
                if let Err(e) = self.apply_effect_with_computed_writes(
                    effect,
                    Some(delta),
                    None,
                    Some(&mut computed_writes),
                ) {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }
        self.flush_computed_write_buffer(&mut computed_writes)?;
        Ok(layer.vertices.len())
    }

    /// Evaluate a layer sequentially with cancellation support via effects pipeline.
    fn evaluate_layer_sequential_cancellable_effects(
        &mut self,
        layer: &super::scheduler::Layer,
        cancel_flag: &AtomicBool,
    ) -> Result<usize, ExcelError> {
        if layer.vertices.len() < COMPUTED_WRITE_COALESCING_MIN_LAYER_WIDTH {
            return self.evaluate_small_layer_direct_effects(
                layer,
                None,
                None,
                Some(cancel_flag),
                256,
                "Evaluation cancelled within layer",
            );
        }

        let mut computed_writes = ComputedWriteBuffer::default();
        for (i, &vertex_id) in layer.vertices.iter().enumerate() {
            if i % 256 == 0 && cancel_flag.load(Ordering::Relaxed) {
                self.flush_computed_write_buffer(&mut computed_writes)?;
                return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                    .with_message("Evaluation cancelled within layer".to_string()));
            }
            self.flush_before_range_dependent_vertex(vertex_id, &mut computed_writes)?;
            let value = match self.evaluate_vertex_immutable(vertex_id) {
                Ok(v) => v,
                Err(e) => LiteralValue::Error(e),
            };
            let effects = match self.plan_vertex_effects_with_computed_flush(
                vertex_id,
                value,
                None,
                &mut computed_writes,
            ) {
                Ok(effects) => effects,
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            };
            for effect in &effects {
                if let Err(e) = self.apply_effect_with_computed_writes(
                    effect,
                    None,
                    None,
                    Some(&mut computed_writes),
                ) {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }
        self.flush_computed_write_buffer(&mut computed_writes)?;
        Ok(layer.vertices.len())
    }

    /// Evaluate a layer sequentially with more frequent cancellation for demand-driven eval.
    fn evaluate_layer_sequential_cancellable_demand_driven_effects(
        &mut self,
        layer: &super::scheduler::Layer,
        cancel_flag: &AtomicBool,
    ) -> Result<usize, ExcelError> {
        if layer.vertices.len() < COMPUTED_WRITE_COALESCING_MIN_LAYER_WIDTH {
            return self.evaluate_small_layer_direct_effects(
                layer,
                None,
                None,
                Some(cancel_flag),
                128,
                "Demand-driven evaluation cancelled within layer",
            );
        }

        let mut computed_writes = ComputedWriteBuffer::default();
        for (i, &vertex_id) in layer.vertices.iter().enumerate() {
            if i % 128 == 0 && cancel_flag.load(Ordering::Relaxed) {
                self.flush_computed_write_buffer(&mut computed_writes)?;
                return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                    .with_message("Demand-driven evaluation cancelled within layer".to_string()));
            }
            self.flush_before_range_dependent_vertex(vertex_id, &mut computed_writes)?;
            let value = match self.evaluate_vertex_immutable(vertex_id) {
                Ok(v) => v,
                Err(e) => LiteralValue::Error(e),
            };
            let effects = match self.plan_vertex_effects_with_computed_flush(
                vertex_id,
                value,
                None,
                &mut computed_writes,
            ) {
                Ok(effects) => effects,
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            };
            for effect in &effects {
                if let Err(e) = self.apply_effect_with_computed_writes(
                    effect,
                    None,
                    None,
                    Some(&mut computed_writes),
                ) {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }
        self.flush_computed_write_buffer(&mut computed_writes)?;
        Ok(layer.vertices.len())
    }

    /// Evaluate a layer in parallel, applying via effects pipeline.
    fn evaluate_layer_parallel_effects(
        &mut self,
        layer: &super::scheduler::Layer,
    ) -> Result<usize, ExcelError> {
        use rayon::prelude::*;

        let thread_pool = self.thread_pool.as_ref().unwrap().clone();

        let mut phase1: Vec<VertexId> = Vec::new();
        let mut phase2: Vec<VertexId> = Vec::new();
        for &vid in &layer.vertices {
            if self.graph.get_range_dependencies(vid).is_some() {
                phase2.push(vid);
            } else {
                phase1.push(vid);
            }
        }

        let inflight: rustc_hash::FxHashSet<VertexId> = layer.vertices.iter().copied().collect();
        let mut applied = 0usize;

        for group in [&phase1[..], &phase2[..]] {
            if group.is_empty() {
                continue;
            }
            let mut computed_writes = ComputedWriteBuffer::default();

            let results: Result<Vec<(VertexId, LiteralValue)>, ExcelError> =
                thread_pool.install(|| {
                    group
                        .par_iter()
                        .map(
                            |&vertex_id| match self.evaluate_vertex_immutable(vertex_id) {
                                Ok(v) => Ok((vertex_id, v)),
                                Err(e) => Ok((vertex_id, LiteralValue::Error(e))),
                            },
                        )
                        .collect()
                });

            match results {
                Ok(vertex_results) => {
                    // Arrays first, then scalars — establishes spill regions before
                    // scalar results that might land inside a spilled region.
                    let mut arrays: Vec<(VertexId, LiteralValue)> = Vec::new();
                    let mut others: Vec<(VertexId, LiteralValue)> = Vec::new();
                    for (vertex_id, result) in vertex_results {
                        if matches!(result, LiteralValue::Array(_)) {
                            arrays.push((vertex_id, result));
                        } else {
                            others.push((vertex_id, result));
                        }
                    }
                    for (vertex_id, result) in arrays {
                        let effects = match self.plan_vertex_effects_with_computed_flush(
                            vertex_id,
                            result,
                            Some(&inflight),
                            &mut computed_writes,
                        ) {
                            Ok(effects) => effects,
                            Err(e) => {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        };
                        for effect in &effects {
                            if let Err(e) = self.apply_effect_with_computed_writes(
                                effect,
                                None,
                                None,
                                Some(&mut computed_writes),
                            ) {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        }
                        applied = applied.saturating_add(1);
                    }
                    // Make all array spill/top-left writes visible before scalar effects in this group.
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    for (vertex_id, result) in others {
                        let effects = match self.plan_vertex_effects_with_computed_flush(
                            vertex_id,
                            result,
                            Some(&inflight),
                            &mut computed_writes,
                        ) {
                            Ok(effects) => effects,
                            Err(e) => {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        };
                        for effect in &effects {
                            if let Err(e) = self.apply_effect_with_computed_writes(
                                effect,
                                None,
                                None,
                                Some(&mut computed_writes),
                            ) {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        }
                        applied = applied.saturating_add(1);
                    }
                    // Flush at the group boundary; phase1 must be visible before phase2.
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                }
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }

        Ok(applied)
    }

    /// Evaluate a layer in parallel with delta collection via effects pipeline.
    fn evaluate_layer_parallel_with_delta_effects(
        &mut self,
        layer: &super::scheduler::Layer,
        delta: &mut DeltaCollector,
    ) -> Result<usize, ExcelError> {
        use rayon::prelude::*;

        let thread_pool = self.thread_pool.as_ref().unwrap().clone();

        let mut phase1: Vec<VertexId> = Vec::new();
        let mut phase2: Vec<VertexId> = Vec::new();
        for &vid in &layer.vertices {
            if self.graph.get_range_dependencies(vid).is_some() {
                phase2.push(vid);
            } else {
                phase1.push(vid);
            }
        }

        let inflight: rustc_hash::FxHashSet<VertexId> = layer.vertices.iter().copied().collect();
        let mut applied = 0usize;

        for group in [&phase1[..], &phase2[..]] {
            if group.is_empty() {
                continue;
            }
            let mut computed_writes = ComputedWriteBuffer::default();
            let results: Result<Vec<(VertexId, LiteralValue)>, ExcelError> =
                thread_pool.install(|| {
                    group
                        .par_iter()
                        .map(
                            |&vertex_id| match self.evaluate_vertex_immutable(vertex_id) {
                                Ok(v) => Ok((vertex_id, v)),
                                Err(e) => Ok((vertex_id, LiteralValue::Error(e))),
                            },
                        )
                        .collect()
                });

            match results {
                Ok(vertex_results) => {
                    let mut arrays: Vec<(VertexId, LiteralValue)> = Vec::new();
                    let mut others: Vec<(VertexId, LiteralValue)> = Vec::new();
                    for (vertex_id, result) in vertex_results {
                        if matches!(result, LiteralValue::Array(_)) {
                            arrays.push((vertex_id, result));
                        } else {
                            others.push((vertex_id, result));
                        }
                    }
                    for (vertex_id, result) in arrays {
                        let effects = match self.plan_vertex_effects_with_computed_flush(
                            vertex_id,
                            result,
                            Some(&inflight),
                            &mut computed_writes,
                        ) {
                            Ok(effects) => effects,
                            Err(e) => {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        };
                        for effect in &effects {
                            if let Err(e) = self.apply_effect_with_computed_writes(
                                effect,
                                Some(delta),
                                None,
                                Some(&mut computed_writes),
                            ) {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        }
                        applied = applied.saturating_add(1);
                    }
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    for (vertex_id, result) in others {
                        let effects = match self.plan_vertex_effects_with_computed_flush(
                            vertex_id,
                            result,
                            Some(&inflight),
                            &mut computed_writes,
                        ) {
                            Ok(effects) => effects,
                            Err(e) => {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        };
                        for effect in &effects {
                            if let Err(e) = self.apply_effect_with_computed_writes(
                                effect,
                                Some(delta),
                                None,
                                Some(&mut computed_writes),
                            ) {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        }
                        applied = applied.saturating_add(1);
                    }
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                }
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }

        Ok(applied)
    }

    /// Evaluate a layer in parallel with cancellation support via effects pipeline.
    fn evaluate_layer_parallel_cancellable_effects(
        &mut self,
        layer: &super::scheduler::Layer,
        cancel_flag: &AtomicBool,
    ) -> Result<usize, ExcelError> {
        use rayon::prelude::*;

        let thread_pool = self.thread_pool.as_ref().unwrap().clone();

        if cancel_flag.load(Ordering::Relaxed) {
            return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                .with_message("Parallel evaluation cancelled before starting".to_string()));
        }

        let mut phase1: Vec<VertexId> = Vec::new();
        let mut phase2: Vec<VertexId> = Vec::new();
        for &vid in &layer.vertices {
            if self.graph.get_range_dependencies(vid).is_some() {
                phase2.push(vid);
            } else {
                phase1.push(vid);
            }
        }

        let inflight: rustc_hash::FxHashSet<VertexId> = layer.vertices.iter().copied().collect();
        let mut applied = 0usize;

        for group in [&phase1[..], &phase2[..]] {
            if group.is_empty() {
                continue;
            }
            let mut computed_writes = ComputedWriteBuffer::default();

            let results: Result<Vec<(VertexId, LiteralValue)>, ExcelError> =
                thread_pool.install(|| {
                    group
                        .par_iter()
                        .map(|&vertex_id| {
                            if cancel_flag.load(Ordering::Relaxed) {
                                return Err(ExcelError::new(ExcelErrorKind::Cancelled)
                                    .with_message(
                                        "Parallel evaluation cancelled during execution"
                                            .to_string(),
                                    ));
                            }
                            match self.evaluate_vertex_immutable(vertex_id) {
                                Ok(v) => Ok((vertex_id, v)),
                                Err(e) => Ok((vertex_id, LiteralValue::Error(e))),
                            }
                        })
                        .collect()
                });

            match results {
                Ok(vertex_results) => {
                    let mut arrays: Vec<(VertexId, LiteralValue)> = Vec::new();
                    let mut others: Vec<(VertexId, LiteralValue)> = Vec::new();
                    for (vertex_id, result) in vertex_results {
                        if matches!(result, LiteralValue::Array(_)) {
                            arrays.push((vertex_id, result));
                        } else {
                            others.push((vertex_id, result));
                        }
                    }
                    for (vertex_id, result) in arrays {
                        let effects = match self.plan_vertex_effects_with_computed_flush(
                            vertex_id,
                            result,
                            Some(&inflight),
                            &mut computed_writes,
                        ) {
                            Ok(effects) => effects,
                            Err(e) => {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        };
                        for effect in &effects {
                            if let Err(e) = self.apply_effect_with_computed_writes(
                                effect,
                                None,
                                None,
                                Some(&mut computed_writes),
                            ) {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        }
                        applied = applied.saturating_add(1);
                    }
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    for (vertex_id, result) in others {
                        let effects = match self.plan_vertex_effects_with_computed_flush(
                            vertex_id,
                            result,
                            Some(&inflight),
                            &mut computed_writes,
                        ) {
                            Ok(effects) => effects,
                            Err(e) => {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        };
                        for effect in &effects {
                            if let Err(e) = self.apply_effect_with_computed_writes(
                                effect,
                                None,
                                None,
                                Some(&mut computed_writes),
                            ) {
                                self.flush_computed_write_buffer(&mut computed_writes)?;
                                return Err(e);
                            }
                        }
                        applied = applied.saturating_add(1);
                    }
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                }
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }

        Ok(applied)
    }

    // ── Top-level evaluate_all_logged ───────────────────────────────────────

    /// Evaluate all dirty/volatile vertices, recording effects into a ChangeLog.
    ///
    /// This is the same flow as `evaluate_all` but threads a ChangeLog through
    /// every effect application so that spill commits/clears are captured.
    pub fn evaluate_all_logged(&mut self, log: &mut ChangeLog) -> Result<EvalResult, ExcelError> {
        self.begin_evaluation_request();
        let _source_cache = self.source_cache_session();
        self.validate_deterministic_mode()?;
        if self.config.defer_graph_building {
            self.build_graph_all()?;
        }
        if self.graph.formula_authority().active_span_count() > 0 {
            return self.evaluate_authoritative_formula_plane_all();
        }
        self.reset_virtual_dep_telemetry_if_disabled();
        let start = crate::instant::FzInstant::now();
        let mut computed_vertices = 0;
        let mut cycle_errors = 0;

        let mut replan_iterations = 0;
        const MAX_REPLAN: usize = 5;
        let mut telemetry = self
            .config
            .enable_virtual_dep_telemetry
            .then(|| self.start_virtual_dep_telemetry());

        log.begin_compound(format!("evaluate_all(epoch={})", self.recalc_epoch));

        loop {
            let to_evaluate = self.graph.get_evaluation_vertices();
            if to_evaluate.is_empty() {
                if let Some(t) = telemetry.as_mut()
                    && t.bailout_reason.is_none()
                {
                    t.bailout_reason = Some("no_work");
                }
                break;
            }

            let (schedule, old_vdeps, meta) = self.create_evaluation_schedule(&to_evaluate)?;
            if let Some(t) = telemetry.as_mut() {
                Self::accumulate_schedule_meta(t, &meta);
            }

            // Walk units in condensation order: stamp cycles at their
            // position, evaluate layers with ChangeLog recording.
            for &unit in &schedule.units {
                match unit {
                    ScheduleUnit::Cycle(i) => {
                        // Journal integration (design doc §4 last row): the
                        // ChangeLog in this path only records SpillClear /
                        // SpillCommit events; WriteCell effects are never
                        // logged (see `apply_write_cell`). Runtime SCC tasks
                        // write values directly and never spill (§7.9 stamps
                        // would-be anchors), and their spill *teardown* is the
                        // same unlogged `stamp_cycle_error` the Static path
                        // already uses here — so direct commits coexist with
                        // the journal cleanly, with identical semantics to
                        // Static. Pinned by `scc_runtime_cycles` tests.
                        if self.handle_cycle_unit(schedule.unit_cycle(i), None, None, None)? > 0 {
                            cycle_errors += 1;
                        }
                    }
                    ScheduleUnit::Layer(i) => {
                        computed_vertices +=
                            self.evaluate_layer_logged(schedule.unit_layer(i), log)?;
                    }
                }
            }

            let changed_vertices = self.changed_virtual_dep_vertices(&to_evaluate, &old_vdeps);
            if let Some(t) = telemetry.as_mut() {
                t.changed_vdeps_total += changed_vertices.len();
            }
            self.graph.clear_dirty_flags(&to_evaluate);
            for v in &changed_vertices {
                self.graph.set_dirty(*v, true);
            }

            if changed_vertices.is_empty() {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("converged");
                }
                break;
            }
            if replan_iterations >= MAX_REPLAN {
                if let Some(t) = telemetry.as_mut() {
                    t.bailout_reason = Some("max_replan");
                }
                break;
            }
            replan_iterations += 1;
        }

        if let Some(mut t) = telemetry {
            t.replan_iterations = replan_iterations;
            self.last_virtual_dep_telemetry = t;
        }

        log.end_compound();

        self.redirty_for_next_recalc();
        self.recalc_epoch = self.recalc_epoch.wrapping_add(1);

        Ok(EvalResult {
            computed_vertices,
            cycle_errors,
            elapsed: start.elapsed(),
        })
    }

    /// Evaluate a single layer with ChangeLog recording.
    fn evaluate_layer_logged(
        &mut self,
        layer: &super::scheduler::Layer,
        log: &mut ChangeLog,
    ) -> Result<usize, ExcelError> {
        let mut computed_writes = ComputedWriteBuffer::default();
        for &vertex_id in &layer.vertices {
            self.flush_before_range_dependent_vertex(vertex_id, &mut computed_writes)?;
            let value = match self.evaluate_vertex_immutable(vertex_id) {
                Ok(v) => v,
                Err(e) => LiteralValue::Error(e),
            };
            let effects = match self.plan_vertex_effects_with_computed_flush(
                vertex_id,
                value,
                None,
                &mut computed_writes,
            ) {
                Ok(effects) => effects,
                Err(e) => {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            };
            for effect in &effects {
                if let Err(e) = self.apply_effect_with_computed_writes(
                    effect,
                    None,
                    Some(log),
                    Some(&mut computed_writes),
                ) {
                    self.flush_computed_write_buffer(&mut computed_writes)?;
                    return Err(e);
                }
            }
        }
        self.flush_computed_write_buffer(&mut computed_writes)?;
        Ok(layer.vertices.len())
    }
}