infino 0.1.6

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright The Infino Authors

//! In-memory manifest types: `ManifestSnapshot`, `SuperfileEntry`,
//! `VectorSummary`. Per-column skip stats live on `SuperfileEntry` as
//! `HashMap<String, ScalarStatsAgg>` (scalar) and
//! `HashMap<String, FtsSummaryAgg>` (FTS).
//!
//! `ManifestSnapshot` is the single immutable point-in-time view of which
//! superfiles exist. `Supertable` holds the current manifest behind
//! an `ArcSwap<ManifestSnapshot>`; commits build a new `ManifestSnapshot` (superfiles:
//! old + new) and atomically swap it in. Readers
//! `ArcSwap::load_full` once at construction to pin a snapshot for
//! the lifetime of their queries.
//!
//! ## Construction is copy-on-write
//!
//! `ManifestSnapshot::with_appended` clones the outer `Vec` and shares each
//! existing `Arc<SuperfileEntry>` between the old and new manifests,
//! so the only per-commit allocation is the new entries plus the
//! `Vec` header. `ManifestSnapshot` itself is immutable — never mutated in
//! place — which is what makes lock-free reader-writer isolation
//! possible.

pub mod aggregates;
pub mod bloom;
pub mod commit;
pub mod disk_cache;
pub mod encoding;
pub mod hll;
pub mod list;
pub mod list_prune;
pub mod options_hash;
pub mod part;
pub mod partition;
pub mod term_range;

use std::{
    cmp::Ordering,
    collections::{BTreeMap, HashMap, HashSet},
    f32::consts::PI,
    fmt,
    ops::Deref,
    sync::{Arc, OnceLock},
};

use arrow::compute::kernels::aggregate as agg;
use arrow_array::*;
use arrow_schema::{DataType, TimeUnit};
use bytes::Bytes;
use dashmap::DashMap;
use futures::future;
/// Re-export the per-column skip aggregates so callers can refer to them as
/// `manifest::ScalarStatsAgg` / `manifest::FtsSummaryAgg` (the value types of
/// `SuperfileEntry.scalar_stats` / `SuperfileEntry.fts_summary`).
pub use list::{FtsSummaryAgg, GlobalVectorIndex, RoutingRef, ScalarStatsAgg};
use rayon::{ThreadPool, prelude::*};
use tokio::{sync::OnceCell, task::spawn_blocking};
use uuid::Uuid;
use xxhash_rust::xxh3::xxh3_64;

use super::options::SupertableOptions;
use crate::{
    storage::{StorageError, StorageProvider},
    superfile::{
        builder::VectorConfig,
        vector::{
            distance::{
                COSINE_DISTANCE_BASE, L2_CROSS_TERM_COEFF, Metric, all_centroid_scores_transposed,
                distance, dot, insert_ranked, nearest_k_centroids_transposed,
                transpose_centroids_cluster_major,
            },
            layout::VectorLayout,
            quant::BitQuantizer,
            rotation::RandomRotation,
        },
    },
    supertable::{
        CommitError,
        error::ManifestError,
        manifest::{
            commit::{
                EncodedPart, PointerFile, frame_content_size, part_uri, read_pointer,
                translate_contention, write_manifest, write_part_bytes, write_pointer,
            },
            disk_cache::ManifestDiskCache,
            encoding::SummaryWireMode,
            list::{
                FORMAT_VERSION as LIST_FORMAT_VERSION, Manifest, ManifestPartEntry,
                PartitionStrategy,
            },
            part::{ContentHash, ManifestPart, PartId},
            partition::{assign_partition, encode_partition_key},
        },
        query::{hierarchical_iter, prune::PruneLeaf},
        slow_vector_state,
    },
};

/// Object-store / LocalFS directory prefix under which committed superfile
/// bytes live (`<data>/seg-<id>.sf.parquet`). Shared by [`SuperfileUri::storage_path`]
/// and the GC live-set sweep so both agree on the superfile namespace.
pub(crate) const SUPERFILE_DATA_DIR: &str = "data";

/// Legacy storage-subtree prefix for the hidden vector-index sibling
/// supertable — the commit-time default stamped when a vector table's
/// manifest carries no explicit prefix. New tables generate a unique
/// prefix at create; this constant only keeps pre-prefix tables readable.
pub(crate) const DEFAULT_VECTOR_INDEX_PREFIX: &str = "_vector_index";

/// One immutable point-in-time view of the supertable.
///
/// **Construction is copy-on-write.** Adding a superfile via
/// [`ManifestSnapshot::with_appended`] returns a new `ManifestSnapshot` whose
/// `superfiles` is `Vec::clone()` + new entries appended; the original
/// `ManifestSnapshot`'s `superfiles` is unchanged. `Arc<SuperfileEntry>` shares
/// the underlying entries between the old and new manifests so the
/// only per-commit allocation is the outer `Vec` and the new
/// entries themselves.
///
/// **Reader isolation.** Readers `ArcSwap::load_full` an
/// `Arc<ManifestSnapshot>` at construction and hold it for their lifetime.
/// New commits don't affect them. Old manifests are dropped
/// automatically once no reader holds an Arc to them.
///
/// `ManifestSnapshot` is the outer hierarchical wrapper (it adds the
/// `list` / `parts` / `loader` persistence-side fields);
/// `SuperfileList` is the flat in-process view that `ManifestSnapshot`
/// derefs to, so callers can access `.manifest_id`,
/// `.superfiles[i]`, `.n_docs_total()` etc. directly through a
/// `ManifestSnapshot`.
#[derive(Debug, Clone)]
pub struct SuperfileList {
    /// Monotonic point-in-time identifier. Starts at 0 (empty
    /// initial manifest from `Supertable::create`); each commit
    /// derives `manifest_id = old.manifest_id + 1`. With a single
    /// writer at a time, no separate counter or atomic is needed —
    /// the read-then-store sequence is exclusive by construction.
    pub manifest_id: u64,
    /// Pointer back to the immutable per-supertable configuration.
    /// Same Arc across all manifests of one supertable.
    pub options: Arc<SupertableOptions>,
    /// Append-only list of superfile entries. Each entry's `Arc`-share
    /// is what makes the copy-on-write per-commit construction
    /// cheap.
    pub superfiles: Vec<Arc<SuperfileEntry>>,
    /// Hidden vector-index sibling prefix. Set at create before the
    /// first manifest list is persisted; cleared once loaded from list.
    pub(crate) vector_index_storage_prefix: Option<String>,
}

impl SuperfileList {
    /// Empty initial state at `manifest_id = 0`.
    pub fn empty(options: Arc<SupertableOptions>) -> Self {
        Self {
            manifest_id: 0,
            options,
            superfiles: Vec::new(),
            vector_index_storage_prefix: None,
        }
    }

    pub(crate) fn empty_with_vector_index_prefix(
        options: Arc<SupertableOptions>,
        vector_index_storage_prefix: Option<String>,
    ) -> Self {
        Self {
            manifest_id: 0,
            options,
            superfiles: Vec::new(),
            vector_index_storage_prefix,
        }
    }

    /// Build a successor SuperfileList with `new_entries` appended to
    /// the end of `superfiles`. Original is unchanged. `manifest_id`
    /// of the result is `self.manifest_id + 1`.
    pub fn with_appended(&self, new_entries: Vec<Arc<SuperfileEntry>>) -> Self {
        let mut superfiles = self.superfiles.clone();
        superfiles.extend(new_entries);
        Self {
            manifest_id: self.manifest_id + 1,
            options: self.options.clone(),
            superfiles,
            vector_index_storage_prefix: self.vector_index_storage_prefix.clone(),
        }
    }

    /// Total documents across all superfiles.
    pub fn n_docs_total(&self) -> u64 {
        self.superfiles.iter().map(|s| s.n_docs).sum()
    }
}

/// The hierarchical manifest. Outer wrapper around the
/// [`SuperfileList`] (flat in-process view) plus the
/// persistence-side metadata:
///
/// - `list`: the [`Manifest`] when this manifest was loaded
///   from / persisted to storage. `None` for in-process-only
///   supertables (no storage attached).
/// - `parts`: per-part lazy-load cache. `OnceCell` per part
///   coalesces concurrent `part(id)` calls into a single
///   `StorageProvider::get` — 100 query tasks on a cold part
///   issue exactly one load.
/// - `loader`: pulls part bytes through the storage provider
///   and verifies content hash. `None` when no storage is
///   attached (the in-process-only path).
///
/// `Deref` exposes the [`SuperfileList`] fields directly so
/// `manifest.manifest_id`, `manifest.superfiles[i]`,
/// `manifest.n_docs_total()` etc. work through a `ManifestSnapshot`
/// reference.
///
/// [`Manifest`]: list::Manifest
pub struct ManifestSnapshot {
    superfile_list: SuperfileList,
    list: Option<Manifest>,
    parts: DashMap<PartId, Arc<OnceCell<Arc<ManifestPart>>>>,
    loader: Option<Arc<ManifestPartLoader>>,
    /// Stamped partition strategy before the first list lands, or
    /// when updating strategy without rebuilding options.
    stamped_partition_strategy: Option<PartitionStrategy>,
    /// Stamped global vector grid before the first list lands (mirrors
    /// `stamped_partition_strategy`): the user commit bootstraps the grid into
    /// this on the first commit-with-vectors, and `update` reads it back via
    /// [`ManifestSnapshot::get_global_vector_index`] to persist it into the new list.
    stamped_global_vector_index: Option<list::GlobalVectorIndex>,
    /// Stamped drained-version set before the (hidden) list lands. The drain
    /// advances this via [`ManifestSnapshot::with_drained_ranges`] and `update` reads
    /// it back via [`ManifestSnapshot::get_drained_ranges`] to persist it. Hidden
    /// manifest only.
    stamped_drained_ranges: Option<list::DrainedVersionRanges>,
}

impl fmt::Debug for ManifestSnapshot {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("ManifestSnapshot")
            .field("manifest_id", &self.superfile_list.manifest_id)
            .field("n_superfiles", &self.superfile_list.superfiles.len())
            .field("has_list", &self.list.is_some())
            .field(
                "n_parts",
                &self.list.as_ref().map(|l| l.parts.len()).unwrap_or(0),
            )
            .field("n_parts_loaded", &self.parts.len())
            .field("has_loader", &self.loader.is_some())
            .finish()
    }
}

impl Deref for ManifestSnapshot {
    type Target = SuperfileList;
    fn deref(&self) -> &Self::Target {
        &self.superfile_list
    }
}

impl ManifestSnapshot {
    pub fn new(
        manifest_id: u64,
        options: Arc<SupertableOptions>,
        superfile_list: Vec<Arc<SuperfileEntry>>,
        storage: Option<Arc<dyn StorageProvider>>,
        list: Option<Manifest>,
    ) -> Self {
        let superfile_list = SuperfileList {
            manifest_id,
            options,
            superfiles: superfile_list,
            vector_index_storage_prefix: None,
        };
        if let Some(storage) = storage
            && let Some(list) = list
        {
            let manifest_cache = superfile_list.options.manifest_disk_cache.clone();
            let loader = Arc::new(ManifestPartLoader::new_with_cache(
                Arc::clone(&storage),
                &list,
                manifest_cache,
            ));
            Self {
                superfile_list,
                list: Some(list),
                parts: DashMap::new(),
                loader: Some(loader),
                stamped_partition_strategy: None,
                stamped_global_vector_index: None,
                stamped_drained_ranges: None,
            }
        } else {
            Self {
                superfile_list,
                list: None,
                parts: DashMap::new(),
                loader: None,
                stamped_partition_strategy: None,
                stamped_global_vector_index: None,
                stamped_drained_ranges: None,
            }
        }
    }

    #[cfg(test)]
    pub fn new_from_superfiles(
        opts: Arc<SupertableOptions>,
        superfiles: Vec<Arc<SuperfileEntry>>,
    ) -> Self {
        ManifestSnapshot::empty(opts).with_appended(superfiles)
    }

    /// Empty initial manifest at `manifest_id = 0`. Used by
    /// `Supertable::create` when no storage is attached.
    pub fn empty(options: Arc<SupertableOptions>) -> Self {
        Self {
            superfile_list: SuperfileList::empty(options),
            list: None,
            parts: DashMap::new(),
            loader: None,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        }
    }

    pub(crate) fn empty_with_vector_index_prefix(
        options: Arc<SupertableOptions>,
        vector_index_storage_prefix: Option<String>,
    ) -> Self {
        Self {
            superfile_list: SuperfileList::empty_with_vector_index_prefix(
                options,
                vector_index_storage_prefix,
            ),
            list: None,
            parts: dashmap::DashMap::new(),
            loader: None,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        }
    }

    /// A *materialized* empty manifest at `manifest_id = 0`, ready to persist.
    /// Unlike [`Self::empty`] (which is in-process-only, `list: None`), this
    /// carries a `Some(list)`, so [`Self::write`] emits the initial (empty)
    /// manifest list + pointer. `Supertable::create` persists this on durable
    /// storage so the table is openable immediately — before its first append,
    /// after a reopen, or from another process — without shifting the
    /// `manifest_id` sequence (the first append still commits `manifest_id 1`).
    /// `vector_index_storage_prefix` is the hidden-sibling subtree the caller
    /// generated at create (`None` for tables without vector columns, and for
    /// the hidden sibling itself).
    pub(crate) fn materialized_empty_with_vector_index_prefix(
        options: Arc<SupertableOptions>,
        vector_index_storage_prefix: Option<String>,
    ) -> Self {
        let strategy = options.effective_partition_strategy();
        let list = Self::build_list(
            &options,
            strategy,
            0,
            Vec::new(),
            vector_index_storage_prefix.clone(),
            BTreeMap::new(),
        );
        let loader = options.storage.as_ref().map(|storage| {
            Arc::new(ManifestPartLoader::new_with_cache(
                storage.clone(),
                &list,
                options.manifest_disk_cache.clone(),
            ))
        });
        Self {
            superfile_list: SuperfileList::empty_with_vector_index_prefix(
                options,
                vector_index_storage_prefix,
            ),
            list: Some(list),
            parts: DashMap::new(),
            loader,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        }
    }

    /// Build a manifest list from the supertable `options` at `manifest_id`,
    /// carrying `parts` and the tombstone-seq state. Shared by the commit path
    /// ([`Self::update`]), and the initial empty-manifest materialization
    /// ([`Self::materialized_empty_with_vector_index_prefix`]), so the
    /// options→list field mapping lives in one place.
    fn build_list(
        options: &SupertableOptions,
        strategy: PartitionStrategy,
        manifest_id: u64,
        parts: Vec<ManifestPartEntry>,
        vector_index_storage_prefix: Option<String>,
        tombstone_seqs: BTreeMap<Uuid, u64>,
    ) -> Manifest {
        Manifest {
            format_version: LIST_FORMAT_VERSION.into(),
            manifest_id,
            options_hash: options_hash::compute_options_hash(options, &strategy),
            schema: Vec::new(),
            id_column: options.id_column.clone(),
            fts_columns: options
                .fts_columns
                .iter()
                .map(|f| list::FtsColumnInfo {
                    column: f.column.clone(),
                })
                .collect(),
            vector_columns: options
                .vector_columns
                .iter()
                .map(|v| list::VectorColumnInfo {
                    column: v.column.clone(),
                    dim: v.dim,
                    n_cent: v.n_cent,
                    rot_seed: v.rot_seed,
                    metric: format!("{:?}", v.metric).to_lowercase(),
                })
                .collect(),
            partition_strategy: strategy,
            vector_index_storage_prefix,
            global_vector_index: None,
            drained_ranges: Default::default(),
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts,
            tombstone_seqs,
        }
    }

    pub fn get_manifest_id(&self) -> u64 {
        self.superfile_list.manifest_id
    }

    pub fn get_next_manifest_id(&self) -> u64 {
        self.get_manifest_id() + 1
    }

    pub fn get_opts(&self) -> Arc<SupertableOptions> {
        self.superfile_list.options.clone()
    }

    pub fn get_partition_strategy(&self) -> list::PartitionStrategy {
        self.partition_strategy()
            .cloned()
            .unwrap_or_else(|| self.superfile_list.options.effective_partition_strategy())
    }

    /// Borrow the resident partition strategy when one is stamped or listed.
    ///
    /// Prefer this on the query path over [`Self::get_partition_strategy`]: a
    /// `VectorCell` strategy owns [`ClusterCentroids`], and cloning it drops
    /// (or re-copies) the transposed SIMD cache used by cell ranking.
    pub(crate) fn partition_strategy(&self) -> Option<&list::PartitionStrategy> {
        self.stamped_partition_strategy
            .as_ref()
            .or_else(|| self.list.as_ref().map(|l| &l.partition_strategy))
    }

    /// [`CellRoutingParams`] from a `VectorCell` strategy, without cloning
    /// the cell-centroid grid.
    pub(crate) fn vector_cell_routing(&self) -> Option<list::CellRoutingParams> {
        match self.partition_strategy() {
            Some(list::PartitionStrategy::VectorCell { routing, .. }) => Some(*routing),
            _ => None,
        }
    }

    /// Borrow the `VectorCell` centroid grid when it matches `column`.
    pub(crate) fn vector_cell_clusters(&self, column: &str) -> Option<&ClusterCentroids> {
        match self.partition_strategy() {
            Some(list::PartitionStrategy::VectorCell {
                column: cell_column,
                clusters,
                ..
            }) if cell_column == column => Some(clusters),
            _ => None,
        }
    }

    /// The global vector cell-index grid this (user) table owns, or `None`
    /// before the first commit-with-vectors. Honors the in-memory stamp set by
    /// [`ManifestSnapshot::with_global_vector_index`] before the first list lands, then
    /// the persisted list.
    ///
    /// Cloning cost: this returns an owned [`list::GlobalVectorIndex`]. The
    /// query path must use [`Self::global_vector_index`] instead so the
    /// transposed centroid cache stays resident across warm queries.
    pub fn get_global_vector_index(&self) -> Option<list::GlobalVectorIndex> {
        self.global_vector_index().cloned()
    }

    /// Borrow the global vector cell-index (no clone — keeps the transposed
    /// SIMD cache warm on the query path).
    pub(crate) fn global_vector_index(&self) -> Option<&list::GlobalVectorIndex> {
        self.stamped_global_vector_index.as_ref().or_else(|| {
            self.list
                .as_ref()
                .and_then(|l| l.global_vector_index.as_ref())
        })
    }

    /// Drained user commit-versions recorded on this (hidden) manifest. Honors
    /// the in-memory stamp set by [`ManifestSnapshot::with_drained_ranges`] before the
    /// first list lands, then the persisted list. Empty by default.
    pub fn get_drained_ranges(&self) -> list::DrainedVersionRanges {
        if let Some(d) = &self.stamped_drained_ranges {
            return d.clone();
        }
        self.list
            .as_ref()
            .map(|l| l.drained_ranges.clone())
            .unwrap_or_default()
    }

    pub fn get_num_parts(&self) -> usize {
        self.list.as_ref().map(|l| l.parts.len()).unwrap_or(0)
    }

    pub fn get_num_parts_loaded(&self) -> usize {
        self.parts.len()
    }

    pub fn is_in_process_only(&self) -> bool {
        self.list.is_none()
    }

    /// Return the resident flat membership only when it is known complete.
    ///
    /// In-process manifests are always flat. Part-backed user manifests are
    /// complete when the resident entry count equals the sum recorded in the
    /// list. A loaded slow-state blob is authoritative by construction:
    /// [`Manifest::load`] either hydrates it completely or fails.
    pub(crate) fn complete_flat_superfiles(&self) -> Option<&[Arc<SuperfileEntry>]> {
        match self.list.as_ref() {
            None => Some(&self.superfile_list.superfiles),
            Some(list) if list.slow_vector_state_uri.is_some() => {
                Some(&self.superfile_list.superfiles)
            }
            Some(list) => {
                let expected: u64 = list.parts.iter().map(|entry| entry.n_superfiles).sum();
                (self.superfile_list.superfiles.len() as u64 == expected)
                    .then_some(self.superfile_list.superfiles.as_slice())
            }
        }
    }

    pub(crate) fn vector_index_storage_prefix(&self) -> Option<&str> {
        if let Some(list) = self.list.as_ref()
            && let Some(prefix) = list.vector_index_storage_prefix.as_deref()
        {
            return Some(prefix);
        }
        self.superfile_list.vector_index_storage_prefix.as_deref()
    }

    fn stamp_vector_index_storage_prefix(
        &self,
        vector_columns: &[list::VectorColumnInfo],
    ) -> Option<String> {
        if vector_columns.is_empty() {
            return None;
        }
        if let Some(prefix) = self.vector_index_storage_prefix() {
            return Some(prefix.to_string());
        }
        Some(DEFAULT_VECTOR_INDEX_PREFIX.to_string())
    }

    pub fn get_cached_part_by_id(&self, part_id: &PartId) -> Option<Arc<ManifestPart>> {
        self.parts
            .get(part_id)
            .and_then(|cell| cell.value().get().cloned())
    }

    pub fn get_cached_part_by_list_idx(&self, idx: usize) -> Option<Arc<ManifestPart>> {
        let Some(list) = &self.list else {
            return None;
        };
        let part_id = list.parts[idx].part_id;
        self.get_cached_part_by_id(&part_id)
    }

    /// Load the committed manifest from storage.
    ///
    /// A genuinely absent pointer is [`ManifestLoadError::PointerNotFound`]:
    /// `Supertable::create` persists the initial (empty) pointer, so a
    /// registered table always has one. A missing pointer is therefore the
    /// open-or-create trigger for a never-created table, or a *lost* pointer
    /// on a created one — either way an error the caller sees, never a
    /// silently-empty table (which would mask committed-then-lost data). A
    /// *corrupt* pointer is a different error variant (`PointerParse`) and
    /// also propagates, so corruption is never masked.
    pub(crate) async fn load(
        current_manifest: Option<Arc<Self>>,
        storage: Arc<dyn StorageProvider>,
        options: Option<Arc<SupertableOptions>>,
    ) -> Result<Arc<Self>, ManifestLoadError> {
        // 1. Read the pointer file.
        let (pointer, _) = match read_pointer(storage.as_ref()).await? {
            Some(p) => p,
            None => return Err(ManifestLoadError::PointerNotFound),
        };
        Self::load_with_pointer(current_manifest, storage, options, pointer).await
    }

    /// [`Self::load`] with the pointer already in hand. Split out so
    /// the refresh path can read the pointer itself (conditionally,
    /// via [`probe_pointer`]) and still share the list + parts
    /// loading below.
    pub(crate) async fn load_with_pointer(
        current_manifest: Option<Arc<Self>>,
        storage: Arc<dyn StorageProvider>,
        options: Option<Arc<SupertableOptions>>,
        pointer: PointerFile,
    ) -> Result<Arc<Self>, ManifestLoadError> {
        if let Some(current_manifest) = &current_manifest
            && current_manifest.superfile_list.manifest_id >= pointer.manifest_id
        {
            // Pointer hasn't advanced past our in-memory state —
            return Err(ManifestLoadError::AlreadyLoaded);
        }

        // 2. Load + parse the manifest list.
        let (list_bytes, _) = storage
            .get(&pointer.manifest_uri)
            .await
            .map_err(ManifestLoadError::Storage)?;
        let list = list::decode(&list_bytes).map_err(ManifestLoadError::ListParse)?;

        let options = if let Some(options) = options {
            options
        } else if let Some(current) = &current_manifest {
            current.options.clone()
        } else {
            return Err(ManifestLoadError::ContentHashMismatch {
                expected: "valid options".to_string(),
                actual: "None options".to_string(),
            });
        };

        // Verify the caller's options match the
        // manifest's stamped digest. The all-zero stored
        // hash bypasses validation (legacy + synthetic
        // fixtures).
        let expected_hash = options_hash::compute_options_hash(&options, &list.partition_strategy);
        if let Err(mismatch) = options_hash::verify_options_hash(expected_hash, list.options_hash) {
            return Err(ManifestLoadError::ContentHashMismatch {
                expected: mismatch.expected,
                actual: mismatch.actual,
            });
        }

        // 3. Build the loader, superfiles & parts. Consumer memory mode
        //    loads each part's routing sibling (counts + 1-bit slab, no
        //    fp32) when the list stamps one — the user table's centroid
        //    payload stays in storage, mirroring the slow-blob sibling.
        let loader = Arc::new(ManifestPartLoader::new_with_cache_and_mode(
            Arc::clone(&storage),
            &list,
            options.manifest_disk_cache.clone(),
            options.summary_centroids_from_superfiles,
        ));
        let parts: DashMap<_, _> = DashMap::new();
        let mut all_superfiles: Vec<Arc<SuperfileEntry>> = Vec::new();

        // Slow-CAS hydration. When the list carries a slow-state ref (keyed
        // on presence, never table kind — the user table's slow section is
        // always `None`), the flat view comes from one content-addressed
        // blob instead of the part fan; parts stay lazily loadable for
        // maintenance. The ref survives list-only churn (deleted-id stamps)
        // and is cleared by every membership `update`, so ref-equality with
        // the current manifest proves membership is unchanged — reuse the
        // already-decoded entries with zero I/O. That reuse is what keeps
        // the centroid state memory-resident across manifest versions until
        // the drainer republishes.
        let expected_n_superfiles: Option<u64> = if list.slow_vector_state_uri.is_some() {
            None
        } else {
            Some(list.parts.iter().map(|e| e.n_superfiles).sum())
        };
        // Hydration precedence: (1) slow-ref reuse (zero I/O, zero decode;
        // membership unchanged by construction since every membership
        // `update` clears the ref — this keeps centroid state resident
        // across manifest churn until the drainer republishes);
        // (2) slow-state blob fetch (ref present, one GET);
        // (3) part loading (no ref — the user table always, and the
        //     hidden table mid-maintenance).
        let reused: Option<Vec<Arc<SuperfileEntry>>> = match (
            list.slow_vector_state_uri.as_deref(),
            list.slow_vector_state_content_hash,
        ) {
            (Some(uri), Some(hash)) => current_manifest.as_ref().and_then(|cur| {
                let same_ref = cur.list.as_ref().is_some_and(|cl| {
                    cl.slow_vector_state_uri.as_deref() == Some(uri)
                        && cl.slow_vector_state_content_hash == Some(hash)
                });
                let complete = expected_n_superfiles
                    .is_none_or(|expected| cur.superfile_list.superfiles.len() as u64 == expected);
                (same_ref && complete).then(|| cur.superfile_list.superfiles.clone())
            }),
            _ => None,
        };
        // No silent degradation: a list that carries a slow-state ref IS
        // the entry payload's address — if the blob fails to load, verify,
        // or agree with the list, that is corruption and the load fails
        // loudly. The part fan below serves only manifests without a ref
        // (the user table always; the hidden table mid-maintenance).
        let entries_reused = reused.is_some();
        let hydrated: Option<Vec<Arc<SuperfileEntry>>> = match reused {
            Some(entries) => Some(entries),
            None => match (
                list.slow_vector_state_uri.as_deref(),
                list.slow_vector_state_content_hash,
            ) {
                (Some(uri), Some(hash)) => {
                    // Two-object model: the primary blob is routing-shaped
                    // (counts + 1-bit admit slab, no fp32 — GiBs → MiBs at
                    // 100M docs) and EVERYONE hydrates from it; exact
                    // centroid scores come from the section.
                    let entries = slow_vector_state::load_state(storage.as_ref(), uri, &hash)
                        .await
                        .map_err(|e| ManifestLoadError::SlowStateHydration(e.to_string()))?;
                    if let Some(expected) = expected_n_superfiles
                        && entries.len() as u64 != expected
                    {
                        return Err(ManifestLoadError::SlowStateHydration(format!(
                            "blob entry count {} != list total {expected}",
                            entries.len(),
                        )));
                    }
                    Some(entries)
                }
                _ => None,
            },
        };
        if let Some(entries) = hydrated {
            // Inherit any already-loaded part cells (maintenance reuse);
            // everything else stays an empty OnceCell for on-demand loads.
            for entry in &list.parts {
                let inherited = current_manifest
                    .as_ref()
                    .and_then(|cur| cur.parts.get(&entry.part_id).map(|kv| kv.value().clone()));
                parts.insert(
                    entry.part_id,
                    inherited.unwrap_or_else(|| Arc::new(OnceCell::new())),
                );
            }
            all_superfiles = entries;
        } else if let Some(current_manifest) = &current_manifest {
            // If we have an existing manifest, populate `parts` with
            // existing entries and track missing part IDs for lazy-load.
            let mut missing_part_ids = Vec::new();
            for entry in &list.parts {
                if let Some(existing) = current_manifest.parts.get(&entry.part_id) {
                    parts.insert(entry.part_id, existing.value().clone());
                } else {
                    missing_part_ids.push(entry.part_id);
                }
            }

            let threshold = options.eager_load_threshold_parts as usize;
            let eager = list.parts.len() <= threshold;

            if eager {
                let load_futs = missing_part_ids
                    .iter()
                    .map(|id| {
                        let loader = Arc::clone(&loader);
                        let pid = *id;
                        async move { loader.load(pid).await }
                    })
                    .collect::<Vec<_>>();
                let loaded = future::join_all(load_futs).await;
                for (pid, result) in missing_part_ids.iter().zip(loaded) {
                    let part = result?;
                    let cell = OnceCell::new();
                    cell.set(part).expect("fresh cell");
                    parts.insert(*pid, Arc::new(cell));
                }
                for entry in &list.parts {
                    let cell = parts.get(&entry.part_id).expect("part inserted above");
                    let part = cell
                        .value()
                        .get()
                        .expect("eager-fetched or inherited; must be set");
                    all_superfiles.extend(part.superfiles.iter().cloned());
                }
            } else {
                for pid in &missing_part_ids {
                    parts.insert(*pid, Arc::new(OnceCell::new()));
                }
            }
        } else {
            let n_parts = list.parts.len();
            let threshold = options.eager_load_threshold_parts as usize;
            let eager = n_parts <= threshold;
            if eager {
                // eager-fetching every part (small manifests — fast first query)
                // parallel-fetch every part + populate
                // the flat superfile_list.superfiles view so the
                // iteration-style query paths (`bm25_search`,
                // `vector_search`, `query_sql`) see all superfiles
                // without going through the hierarchical iterator.
                let part_ids: Vec<_> = list.parts.iter().map(|p| p.part_id).collect();
                let load_futs = part_ids
                    .iter()
                    .map(|id| {
                        let loader = Arc::clone(&loader);
                        let pid = *id;
                        async move { loader.load(pid).await }
                    })
                    .collect::<Vec<_>>();
                let loaded = future::join_all(load_futs).await;
                for (pid, result) in part_ids.iter().zip(loaded) {
                    let part = result?;
                    all_superfiles.extend(part.superfiles.iter().cloned());
                    let cell = OnceCell::new();
                    cell.set(part).expect("fresh OnceCell");
                    parts.insert(*pid, Arc::new(cell));
                }
            } else {
                // Lazy path: each part gets an empty
                // `OnceCell`; first `ManifestSnapshot::part(id).await`
                // triggers a single storage GET for that part.
                // `superfile_list.superfiles` stays empty — legacy
                // flat-iteration queries return zero results
                // until the hierarchical query path lands.
                // Callers in lazy mode today drive
                // `ManifestSnapshot::part().await` directly.
                for entry in &list.parts {
                    parts.insert(entry.part_id, Arc::new(OnceCell::new()));
                }
            }
        }

        // HIDDEN manifests (VectorCell partitioning) never hold summary
        // fp32 in RAM — the two-object slow-CAS model stores it once, in
        // the centroid section, and every exact rescore (consumer or
        // maintenance) reads from there. New-era blobs decode straight
        // into the stripped shape (routing wire); this pass covers legacy
        // full-form blobs and inherited entries so the resident shape is
        // uniform regardless of what was fetched. Unconditional — not
        // knob-gated: hidden fine fp32 is the residency pig (~620 MB at
        // 100M). User-table summaries stay resident — they are small
        // (~100 MB at 100M, per-fragment cells), and stripping them
        // forced pre-drain and filtered routing onto 1-bit estimates,
        // which measured filtered recall 0.722 against the 0.95 bar.
        // Grid centroids in the list are untouched.
        // Skip when the entry list was reused from the current manifest:
        // those `Arc`s were stripped and prewarmed by the load that first
        // produced them, and this path also runs on the strong-consistency
        // refresh (query hot path), where a re-walk buys nothing. For fresh
        // entries the strip + slab encode is a CPU wave (rotation +
        // sign-pack per fine centroid, ~1.4 s single-threaded at 100M), so
        // it runs on the blocking pool — not inline on a runtime worker.
        if !entries_reused {
            let strip = matches!(
                list.partition_strategy,
                PartitionStrategy::VectorCell { .. }
            );
            let vector_columns = options.vector_columns.clone();
            let pool = Arc::clone(&options.reader_pool);
            let mut entries = all_superfiles;
            let prewarm = move || {
                if strip {
                    strip_summary_centroids(&mut entries, &vector_columns);
                }
                prewarm_summary_admit_slabs(&entries, &vector_columns, &pool);
                entries
            };
            all_superfiles = match spawn_blocking(prewarm).await {
                Ok(entries) => entries,
                Err(join_error) => {
                    return Err(ManifestLoadError::SlowStateHydration(format!(
                        "admit slab prewarm task failed: {join_error}"
                    )));
                }
            };
        }

        let mut new_superfile_list = SuperfileList::empty(options.clone());
        new_superfile_list.manifest_id = pointer.manifest_id;
        new_superfile_list.superfiles = all_superfiles;
        let new_manifest = ManifestSnapshot {
            superfile_list: new_superfile_list,
            list: Some(list),
            parts,
            loader: Some(loader),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        };

        Ok(Arc::new(new_manifest))
    }

    /// Commit a new manifest version.
    ///
    /// Orchestrates the four-step sequence:
    ///
    /// 1. **In parallel** — write each new manifest part + write
    ///    the new manifest list. Independent of each other; the
    ///    list references parts by URI (= blake3 of bytes,
    ///    computed before any I/O). Issued via
    ///    [`futures::future::join_all`].
    /// 2. Await all of the above (visibility barrier #1: parts
    ///    and list must be durable before the pointer publishes).
    /// 3. Build the new pointer file (manifest_id, manifest_uri,
    ///    list_content_hash).
    /// 4. Conditional pointer-PUT (visibility barrier #2: the
    ///    rename is the only thing readers observe).
    ///
    /// `parts_to_write` should contain **only the parts that need
    /// to be persisted** (i.e., new + changed). Each element is the
    /// pre-encoded (Avro+zstd) bytes produced by [`rebuild_part_and_entry`]
    /// — passing them directly avoids a second encode cycle.
    /// Reused parts from the previous manifest version are not in this
    /// list — their URIs are already in `new_list.parts[i].uri`.
    pub async fn write(
        &self,
        storage: &dyn StorageProvider,
        expected_prev_etag: Option<&str>,
        parts_to_write: &[&[u8]],
    ) -> Result<(), CommitError> {
        let Some(list_to_write) = self.list.as_ref() else {
            return Ok(());
        };
        // Step 1+2: parallel write of (list, parts).
        //
        // Both futures are independent — the list's references to
        // each part's URI are content-addressable from the
        // in-memory bytes before any I/O, so there's no
        // happens-before edge between them.
        let list_fut = write_manifest(storage, list_to_write);
        let part_futs = parts_to_write
            .iter()
            .map(|encoded| write_part_bytes(storage, encoded));
        let part_join = future::join_all(part_futs);

        let (list_res, part_results) = tokio::join!(list_fut, part_join);
        // Translate `Storage(PreconditionFailed)` from sub-writes
        // into `WriteContentionExhausted` so callers (and the
        // writer's OCC retry loop) can match on one variant
        // regardless of which CAS lost the race — list or pointer.
        let list_res = list_res.map_err(translate_contention)?;
        for part_result in part_results {
            part_result.map_err(translate_contention)?;
        }

        // Step 3: build pointer.
        let pointer = PointerFile {
            manifest_id: self.get_manifest_id(),
            manifest_uri: list_res.uri,
            content_hash: list_res.content_hash,
        };

        // Step 4: conditional pointer write — the visibility
        // barrier. Until this succeeds, no reader sees the new
        // manifest version.
        write_pointer(storage, &pointer, expected_prev_etag).await?;
        Ok(())
    }

    pub fn get_all_superfiles(&self) -> &[Arc<SuperfileEntry>] {
        &self.superfile_list.superfiles
    }

    pub(crate) async fn get_pruned_superfiles(
        &self,
        leaves: &[PruneLeaf],
    ) -> Result<Vec<Arc<SuperfileEntry>>, ManifestLoadError> {
        match &self.list {
            Some(list) => {
                if list.slow_vector_state_uri.is_some() {
                    return Ok(self.superfile_list.superfiles.clone());
                }
                // Residency fast path: when the flat view is COMPLETE, the
                // read path must issue zero metadata GETs — serve the
                // resident entries and let the per-entry skips downstream
                // (term ranges, Blooms, min/max on each `SuperfileEntry`)
                // bound the data fetches. Part-level pruning only ever
                // paid off by *avoiding part loads*; with the entries
                // already resident there is nothing to avoid.
                let expected: u64 = list.parts.iter().map(|e| e.n_superfiles).sum();
                if self.superfile_list.superfiles.len() as u64 == expected {
                    return Ok(self.superfile_list.superfiles.clone());
                }
                // Incomplete view (legacy lazy manifests): prune at part
                // granularity and load only the survivors.
                // Intersect each constraining leaf's kept-part set. A leaf
                // with no part pruner (`None`) imposes no constraint.
                let mut kept: Option<HashSet<PartId>> = None;
                for leaf in leaves {
                    if let Some(part_ids) = leaf.keep_parts(list) {
                        let set: HashSet<PartId> = part_ids.into_iter().collect();
                        kept = Some(match kept {
                            None => set,
                            Some(existing) => existing.intersection(&set).copied().collect(),
                        });
                    }
                }
                // Preserve manifest (time) order of the surviving parts.
                let ordered: Vec<PartId> = match kept {
                    Some(set) => list
                        .parts
                        .iter()
                        .map(|p| p.part_id)
                        .filter(|id| set.contains(id))
                        .collect(),
                    None => list.parts.iter().map(|p| p.part_id).collect(),
                };
                hierarchical_iter::load_and_flatten(self, &ordered).await
            }
            None => Ok(hierarchical_iter::fallback_to_flat_superfiles(self)),
        }
    }

    /// All superfile entries, loaded through the hierarchical part loader in
    /// manifest (time) order. Vector search fans over every entry — cell
    /// routing (nearest global centroids) is the selection mechanism, not a
    /// part-level prune.
    pub(crate) async fn get_all_superfiles_loaded(
        &self,
    ) -> Result<Vec<Arc<SuperfileEntry>>, ManifestLoadError> {
        match &self.list {
            Some(list) => {
                if list.slow_vector_state_uri.is_some() {
                    return Ok(self.superfile_list.superfiles.clone());
                }
                // Flat-view fast path: when the resident view is COMPLETE
                // (eager-loaded, blob-hydrated, or update-derived from a
                // complete predecessor) it is exactly the parts' content, so
                // no part loads are needed. Completeness is checked against
                // the list's per-part counts because a LAZY manifest's
                // post-commit flat view is non-empty but incomplete (the new
                // entries only) — returning it would silently drop data.
                let expected: u64 = list.parts.iter().map(|e| e.n_superfiles).sum();
                if self.superfile_list.superfiles.len() as u64 == expected {
                    return Ok(self.superfile_list.superfiles.clone());
                }
                let all: Vec<PartId> = list.parts.iter().map(|p| p.part_id).collect();
                hierarchical_iter::load_and_flatten(self, &all).await
            }
            None => Ok(hierarchical_iter::fallback_to_flat_superfiles(self)),
        }
    }

    /// User superfiles whose logical birth version is not covered by the
    /// hidden drain watermark. Part-level birth ranges prune fully drained
    /// lazy parts before any object-store read.
    pub(crate) async fn get_undrained_superfiles_loaded(
        &self,
        drained: &list::DrainedVersionRanges,
    ) -> Result<Vec<Arc<SuperfileEntry>>, ManifestLoadError> {
        let Some(list) = &self.list else {
            return Ok(self
                .superfile_list
                .superfiles
                .iter()
                .filter(|entry| !drained.contains(entry.birth_version))
                .cloned()
                .collect());
        };
        // A list carrying a slow-state ref hydrated its membership from the
        // blob (hidden manifests write no parts at all), so the resident
        // flat view is authoritative and the parts sum below would be wrong
        // — zero parts would fan out to zero entries and silently drop
        // every undrained superfile.
        if list.slow_vector_state_uri.is_some() {
            return Ok(self
                .superfile_list
                .superfiles
                .iter()
                .filter(|entry| !drained.contains(entry.birth_version))
                .cloned()
                .collect());
        }
        let expected: u64 = list.parts.iter().map(|entry| entry.n_superfiles).sum();
        if self.superfile_list.superfiles.len() as u64 == expected {
            return Ok(self
                .superfile_list
                .superfiles
                .iter()
                .filter(|entry| !drained.contains(entry.birth_version))
                .cloned()
                .collect());
        }
        let part_ids: Vec<PartId> = list
            .parts
            .iter()
            .filter(|entry| {
                entry
                    .birth_version_range()
                    .is_none_or(|(lo, hi)| !drained.covers(lo, hi))
            })
            .map(|entry| entry.part_id)
            .collect();
        let entries = hierarchical_iter::load_and_flatten(self, &part_ids).await?;
        Ok(entries
            .into_iter()
            .filter(|entry| !drained.contains(entry.birth_version))
            .collect())
    }

    pub fn get_all_list_entries(&self) -> &[ManifestPartEntry] {
        match &self.list {
            Some(list) => &list.parts,
            None => &[],
        }
    }

    /// Build a successor manifest with `new_entries` appended.
    /// Preserves the persistence-side metadata (`list`, `loader`)
    /// from the predecessor; the per-part cache is fresh (an empty
    /// `DashMap`) because the parts referenced by the new version
    /// may differ. Cross-version part inheritance via content-
    /// addressed `Arc::clone` lives in `Supertable::refresh`.
    pub fn with_appended(&self, new_entries: Vec<Arc<SuperfileEntry>>) -> Self {
        Self {
            superfile_list: self.superfile_list.with_appended(new_entries),
            list: self.list.clone(),
            parts: DashMap::new(),
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        }
    }

    /// The deleted-`_id` set's encoded bytes carried inline in the list
    /// (zero-GET read path); `None` on manifests stamped before the
    /// inline bytes existed.
    pub(crate) fn deleted_user_ids_inline(&self) -> Option<&[u8]> {
        self.list.as_ref()?.deleted_user_ids_inline.as_deref()
    }

    /// Slow-CAS section accessor: the content-addressed blob holding this
    /// table's superfile entries (drain-owned routing/centroid state), or
    /// `None` when no maintenance has published one — always `None` on the
    /// user table. Consumers key on presence, never on table kind.
    pub(crate) fn slow_vector_state_blob(&self) -> Option<(&str, part::ContentHash)> {
        let list = self.list.as_ref()?;
        Some((
            list.slow_vector_state_uri.as_deref()?,
            list.slow_vector_state_content_hash?,
        ))
    }

    /// Centroid-section sibling of the slow-CAS blob (contiguous fp32 fine
    /// centroids in `(entry, column, cell)` order) — the stripped-summary
    /// admit rescore hydrates it once instead of fanning per-cell superfile
    /// reads. `None` on manifests written before the sibling existed.
    pub(crate) fn slow_vector_state_centroids_blob(&self) -> Option<&RoutingRef> {
        self.list.as_ref()?.slow_vector_state_centroids.as_ref()
    }

    /// Stamp (or replace) the hidden index's consolidated deleted-user-`_id`
    /// bytes in the manifest list. Bumps `manifest_id` like a normal commit
    /// without touching superfiles or parts.
    pub fn with_deleted_user_ids(&self, encoded: Vec<u8>) -> Self {
        let next_id = self.get_next_manifest_id();
        let new_list = self.list.as_ref().map(|list| {
            let mut list = list.clone();
            list.manifest_id = next_id;
            list.deleted_user_ids_inline = Some(encoded.clone());
            list
        });
        Self {
            superfile_list: SuperfileList {
                manifest_id: next_id,
                options: Arc::clone(&self.superfile_list.options),
                superfiles: self.superfile_list.superfiles.clone(),
                vector_index_storage_prefix: self
                    .superfile_list
                    .vector_index_storage_prefix
                    .clone(),
            },
            list: new_list,
            parts: self.parts.clone(),
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        }
    }

    /// Stamp (or replace) the slow-CAS vector-state blob reference — the
    /// content-addressed object holding this table's superfile entries
    /// (drain-owned routing/centroid state). Bumps `manifest_id` like a
    /// normal commit without touching superfiles or parts, mirroring
    /// [`ManifestSnapshot::with_deleted_user_ids`]. Standalone restamp path
    /// (e.g. post-drain refresh); membership commits instead compose the
    /// ref via [`Self::with_slow_vector_state_ref`] before the same CAS.
    pub fn with_slow_vector_state(
        &self,
        uri: String,
        hash: part::ContentHash,
        centroids: RoutingRef,
    ) -> Self {
        let next_id = self.get_next_manifest_id();
        let new_list = self.list.as_ref().map(|list| {
            let mut list = list.clone();
            list.manifest_id = next_id;
            list.slow_vector_state_uri = Some(uri);
            list.slow_vector_state_content_hash = Some(hash);
            list.slow_vector_state_centroids = Some(centroids);
            list
        });
        Self {
            superfile_list: SuperfileList {
                manifest_id: next_id,
                options: Arc::clone(&self.superfile_list.options),
                superfiles: self.superfile_list.superfiles.clone(),
                vector_index_storage_prefix: self
                    .superfile_list
                    .vector_index_storage_prefix
                    .clone(),
            },
            list: new_list,
            parts: self.parts.clone(),
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        }
    }

    /// Stamp the slow-state ref onto an already-built successor **without**
    /// bumping `manifest_id`. Used when composing a membership
    /// [`crate::supertable::writer::try_commit_attempt`] so the blob PUT and
    /// list/pointer CAS publish together — closing the window where a crash
    /// leaves membership durable with a cleared slow-state ref.
    pub(crate) fn with_slow_vector_state_ref(
        &self,
        uri: String,
        hash: part::ContentHash,
        centroids: RoutingRef,
    ) -> Self {
        let new_list = self.list.as_ref().map(|list| {
            let mut list = list.clone();
            list.slow_vector_state_uri = Some(uri);
            list.slow_vector_state_content_hash = Some(hash);
            list.slow_vector_state_centroids = Some(centroids);
            list
        });
        Self {
            superfile_list: SuperfileList {
                manifest_id: self.superfile_list.manifest_id,
                options: Arc::clone(&self.superfile_list.options),
                superfiles: self.superfile_list.superfiles.clone(),
                vector_index_storage_prefix: self
                    .superfile_list
                    .vector_index_storage_prefix
                    .clone(),
            },
            list: new_list,
            parts: self.parts.clone(),
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        }
    }

    /// Stamp (or replace) the partition strategy on this manifest snapshot.
    /// Updates both the persisted list metadata and the in-memory options
    /// fallback used before the first list write lands.
    pub fn with_partition_strategy(&self, strategy: list::PartitionStrategy) -> Self {
        let new_list = match self.list.as_ref() {
            Some(list) => {
                let mut list = list.clone();
                list.partition_strategy = strategy.clone();
                Some(list)
            }
            None => None,
        };
        Self {
            superfile_list: SuperfileList {
                manifest_id: self.manifest_id,
                options: Arc::clone(&self.options),
                superfiles: self.superfiles.clone(),
                vector_index_storage_prefix: self.vector_index_storage_prefix.clone(),
            },
            list: new_list.or_else(|| self.list.clone()),
            parts: self.parts.clone(),
            loader: self.loader.clone(),
            stamped_partition_strategy: Some(strategy),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        }
    }

    /// Stamp (or replace) the global vector cell-index grid on this snapshot.
    /// Mirrors [`ManifestSnapshot::with_partition_strategy`]: updates the persisted list
    /// metadata when present, and the in-memory stamp used before the first
    /// list write lands (the first commit-with-vectors).
    pub fn with_global_vector_index(&self, index: list::GlobalVectorIndex) -> Self {
        let new_list = self.list.as_ref().map(|list| {
            let mut list = list.clone();
            list.global_vector_index = Some(index.clone());
            list
        });
        Self {
            superfile_list: SuperfileList {
                manifest_id: self.manifest_id,
                options: Arc::clone(&self.options),
                superfiles: self.superfiles.clone(),
                vector_index_storage_prefix: self.vector_index_storage_prefix.clone(),
            },
            list: new_list.or_else(|| self.list.clone()),
            parts: self.parts.clone(),
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: Some(index),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        }
    }

    /// Stamp the drained user commit-versions on this (hidden) snapshot, so the
    /// next `update`/commit persists them. Mirrors the other stampers: updates
    /// the list when present, and the in-memory stamp before the first hidden
    /// list lands. The drain calls this with the advanced set in the same
    /// commit that appends the batch's cells (atomic via the manifest CAS).
    pub fn with_drained_ranges(&self, ranges: list::DrainedVersionRanges) -> Self {
        let new_list = self.list.as_ref().map(|list| {
            let mut list = list.clone();
            list.drained_ranges = ranges.clone();
            list
        });
        Self {
            superfile_list: SuperfileList {
                manifest_id: self.manifest_id,
                options: Arc::clone(&self.options),
                superfiles: self.superfiles.clone(),
                vector_index_storage_prefix: self.vector_index_storage_prefix.clone(),
            },
            list: new_list.or_else(|| self.list.clone()),
            parts: self.parts.clone(),
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: Some(ranges),
        }
    }

    /// The persisted list's per-superfile tombstone-seq map. `None`
    /// for in-process-only manifests (no persisted list ⇒ no sidecars
    /// can exist).
    pub fn get_tombstone_seqs(&self) -> Option<&BTreeMap<Uuid, u64>> {
        self.list.as_ref().map(|l| &l.tombstone_seqs)
    }

    /// Build a successor manifest identical to `self` except that every
    /// superfile in `touched` has its tombstone seq set to the successor's
    /// `manifest_id`. This is the mutation pipeline's post-sidecar stamp:
    /// no superfile entries or parts change, so persisting the successor
    /// is a list + pointer write only (empty `parts_to_write`).
    ///
    /// Returns `None` for in-process-only manifests (no persisted list —
    /// nothing to stamp, and no cross-process readers to inform).
    pub(crate) fn with_tombstone_seqs_bumped(&self, touched: &[Uuid]) -> Option<Self> {
        let list = self.list.as_ref()?;
        let next_id = self.get_next_manifest_id();
        let mut new_list = list.clone();
        new_list.manifest_id = next_id;
        for id in touched {
            new_list.tombstone_seqs.insert(*id, next_id);
        }
        let mut superfile_list = self.superfile_list.clone();
        superfile_list.manifest_id = next_id;
        // Same parts as the predecessor — inherit the loaded-part cache
        // wholesale so the stamp never forces a part re-fetch.
        let parts = DashMap::new();
        for kv in self.parts.iter() {
            parts.insert(*kv.key(), Arc::clone(kv.value()));
        }
        Some(Self {
            superfile_list,
            list: Some(new_list),
            parts,
            loader: self.loader.clone(),
            stamped_partition_strategy: self.stamped_partition_strategy.clone(),
            stamped_global_vector_index: self.stamped_global_vector_index.clone(),
            stamped_drained_ranges: self.stamped_drained_ranges.clone(),
        })
    }

    /// Lazy-load entry point for manifest parts.
    ///
    /// Concurrent callers on the same not-yet-loaded `part_id`
    /// share a single `StorageProvider::get` via the per-part
    /// `tokio::sync::OnceCell` — 100 concurrent queries on a
    /// cold part see exactly one load.
    ///
    /// Errors:
    /// - `OpenError::Build(BuildError::Store(...))` if no loader
    ///   is attached (in-process-only manifest).
    /// - `OpenError::ContentHashMismatch` if the loaded part's
    ///   blake3 doesn't match the manifest list's recorded hash.
    /// - `OpenError::ManifestPartParse { … }` for Avro / zstd
    ///   decode failures.
    pub async fn get_part_by_id(
        &self,
        part_id: PartId,
    ) -> Result<Arc<ManifestPart>, ManifestLoadError> {
        let loader = self
            .loader
            .as_ref()
            .ok_or(ManifestLoadError::NoLoaderAttached)?;
        let cell = self
            .parts
            .entry(part_id)
            .or_insert_with(|| Arc::new(OnceCell::new()))
            .clone();
        let loaded = cell.get_or_try_init(|| loader.load(part_id)).await?;
        Ok(Arc::clone(loaded))
    }

    /// Fp32 fine centroids for this USER manifest's stripped summary
    /// cells, hydrated once per manifest generation from the FULL
    /// manifest parts — the user table's content-addressed store for
    /// summary fp32, mirroring what the slow-CAS centroid section does
    /// for the hidden table. Consumers under
    /// `summary_centroids_from_superfiles` open with routing parts
    /// (1-bit slabs, no fp32); the first rescore pays one full-part wave
    /// (bytes land in the manifest disk cache), then every query scores
    /// from RAM. User summaries are per-fragment cells, small enough to
    /// keep resident. `None` when this is a hidden (cell-partitioned)
    /// manifest — its rescore reads the spilled centroid section — or
    /// when no loader/parts exist (entries are inline and unstripped).
    pub(crate) async fn user_centroids_for_rescore(&self) -> Option<Arc<UserCentroidCache>> {
        let list = self.list.as_ref()?;
        if matches!(
            list.partition_strategy,
            PartitionStrategy::VectorCell { .. }
        ) {
            return None;
        }
        let loader = self.loader.as_ref()?;
        if list.parts.is_empty() {
            return None;
        }
        let manifest_id = self.get_manifest_id();
        let slot = Arc::clone(&self.options.user_centroid_cache);
        let mut guard = slot.lock().await;
        if let Some(cache) = guard.as_ref()
            && cache.manifest_id == manifest_id
        {
            return Some(Arc::clone(cache));
        }
        // Full-form loads bypass the snapshot's part cells (those hold the
        // routing-decoded form on knob-on consumers); the loader's disk
        // cache still dedups bytes across generations by content hash.
        let waves = list.parts.iter().map(|part| {
            let loader = Arc::clone(loader);
            let part_id = part.part_id;
            async move { loader.load_full(part_id).await }
        });
        match future::try_join_all(waves).await {
            Ok(parts) => {
                let cache = Arc::new(UserCentroidCache::from_parts(manifest_id, &parts));
                *guard = Some(Arc::clone(&cache));
                Some(cache)
            }
            Err(error) => {
                eprintln!(
                    "[supertable] full-part centroid hydration unavailable ({error}); falling \
                     back to per-superfile centroid reads"
                );
                None
            }
        }
    }

    /// Resolve one superfile by storage URI. Checks the flat
    /// [`SuperfileList::superfiles`] view first; when the entry is absent
    /// there (lazy list/parts layout), walks manifest parts until a match
    /// is found.
    pub(crate) async fn lookup_superfile_entry(
        &self,
        uri: SuperfileUri,
    ) -> Result<Option<Arc<SuperfileEntry>>, ManifestLoadError> {
        if let Some(entry) = self.superfiles.iter().find(|e| e.uri == uri) {
            return Ok(Some(Arc::clone(entry)));
        }
        let Some(list) = &self.list else {
            return Ok(None);
        };
        for part_entry in &list.parts {
            let part = self.get_part_by_id(part_entry.part_id).await?;
            if let Some(entry) = part.superfiles.iter().find(|e| e.uri == uri) {
                return Ok(Some(Arc::clone(entry)));
            }
        }
        Ok(None)
    }

    /// Returns the new ManifestPartEntries when `new_entries` are added to `old` manifest. This
    /// operation may create new ManifestParts. The function also returns the new ManifestParts that
    /// the caller can decide to write to storage.
    pub async fn update(
        &self,
        new_entries: &[Arc<SuperfileEntry>],
        entries_to_remove: &[Arc<SuperfileEntry>],
    ) -> Result<(ManifestSnapshot, Vec<EncodedPart>), ManifestError> {
        self.update_inner(new_entries, entries_to_remove, false)
            .await
    }

    /// Compaction replaces physical files without changing the logical user
    /// commits already represented by those files. Preserve each replacement
    /// entry's inherited `birth_version` so the hidden drain watermark keeps
    /// recognizing that data as drained.
    pub(crate) async fn update_preserving_birth_versions(
        &self,
        new_entries: &[Arc<SuperfileEntry>],
        entries_to_remove: &[Arc<SuperfileEntry>],
    ) -> Result<(ManifestSnapshot, Vec<EncodedPart>), ManifestError> {
        self.update_inner(new_entries, entries_to_remove, true)
            .await
    }

    async fn update_inner(
        &self,
        new_entries: &[Arc<SuperfileEntry>],
        entries_to_remove: &[Arc<SuperfileEntry>],
        preserve_birth_versions: bool,
    ) -> Result<(ManifestSnapshot, Vec<EncodedPart>), ManifestError> {
        // 1. Resolve the effective partition strategy. Locked at
        //    first commit: read from the existing manifest list
        //    if present, else use the options default.
        let opts = self.get_opts();
        let strategy = self.get_partition_strategy();
        // Part wire form follows the LOCKED strategy, not raw options: a
        // handle opened with a mismatched partition option must never flip
        // a user part to routing-only wire (that would drop its fp32
        // summaries durably, with no sibling to recover from).
        let hidden_table = matches!(&strategy, PartitionStrategy::VectorCell { .. });

        // 2. Stamp each new entry with its partition key — this also validates
        //    against the strategy (surfaces SuperfileSpansPartition /
        //    unsupported-column-type / missing-partition_hint at commit). The
        //    partition lives on the ENTRY, not the part: parts are size-bucketed
        //    at the table level (below), so a part spans partitions and carries
        //    no key of its own. A reader recovers each superfile's partition
        //    from its entry in the part, with no data-file open. Assignment
        //    runs at commit time, so e.g. IngestionTime resolves to the current
        //    day bucket.
        //
        //    Entries must arrive unstamped (empty partition_key): the key is
        //    derived here, and every source of new entries — the writer,
        //    compaction (a merged superfile is a fresh entry), WAL replay —
        //    builds them with an empty key. A non-empty key would mean an
        //    earlier stage stamped it; committing would silently re-derive and
        //    overwrite that assignment (e.g. shifting an IngestionTime entry to
        //    the current day), so reject it instead.
        //
        //    Fresh writes stamp each new entry's `birth_version` to this
        //    commit's version. Compaction instead preserves the oldest input
        //    version inherited by its replacement: changing physical files
        //    does not make already-drained logical data undrained.
        let birth_version = self.get_next_manifest_id();
        let stamped_new_entries: Vec<Arc<SuperfileEntry>> = new_entries
            .iter()
            .map(|e| {
                if !e.partition_key.is_empty() {
                    return Err(ManifestError::EntryAlreadyPartitioned {
                        detail: format!(
                            "superfile {} arrived with a partition_key already set",
                            e.superfile_id
                        ),
                    });
                }
                let pk = assign_partition(e, &strategy)?;
                let entry_birth_version = if preserve_birth_versions {
                    e.birth_version
                } else {
                    birth_version
                };
                Ok(Arc::new(SuperfileEntry {
                    partition_key: encode_partition_key(&pk),
                    birth_version: entry_birth_version,
                    ..(**e).clone()
                }))
            })
            .collect::<Result<_, ManifestError>>()?;

        // 3. One table-level lineage: new entries append to the last (latest)
        //    part — rewriting it, or splitting into a fresh part when it would
        //    exceed target_superfiles_per_part — while earlier parts carry over
        //    unchanged (same content-hash + URI, no re-encode / PUT). When there
        //    is no prior part, the new entries form the first one. The partition
        //    tag stays on each entry (routing + zone-map input); it no longer
        //    dictates part boundaries, so a query prunes parts by their
        //    aggregates and filters the surviving entries by tag in memory.
        // User tables persist membership in manifest parts. Hidden VectorCell
        // tables persist membership/routing in the slow-CAS blob instead, so
        // `None` skips part creation/rewrite entirely; the existing drain /
        // compaction slow-state publication remains the sole hidden store.
        let list_entries: Option<&[ManifestPartEntry]> =
            if matches!(&strategy, PartitionStrategy::VectorCell { .. }) {
                None
            } else {
                Some(self.get_all_list_entries())
            };
        let latest_idx = list_entries.and_then(|entries| entries.len().checked_sub(1));
        let mut out_list_entries: Vec<ManifestPartEntry> = Vec::new();
        let mut parts_to_write: Vec<EncodedPart> = Vec::new();
        let mut pending_new = list_entries
            .map(|_| stamped_new_entries.to_vec())
            .unwrap_or_default();

        for (i, entry) in list_entries.unwrap_or_default().iter().enumerate() {
            if Some(i) != latest_idx || pending_new.is_empty() {
                out_list_entries.push(entry.clone());
                continue;
            }
            let new_for_part = std::mem::take(&mut pending_new);
            let combined_n = entry.n_superfiles + new_for_part.len() as u64;
            // Freeze the latest part once it reaches either soft cap — the
            // superfile-count target or the compressed-size threshold. Absorbing
            // appends into an already-fat part re-encodes and re-PUTs its whole
            // payload every commit (O(part bytes) commit cost, plus an orphaned
            // part object per commit); splitting keeps prior parts immutable,
            // which is the point of the part scheme. Size matters independently
            // of count for vector tables: cell-packed entries carry fine
            // centroids, so a handful of entries can outweigh thousands of
            // scalar-only ones.
            let latest_at_size_cap = entry.size_bytes_compressed
                >= self.superfile_list.options.part_size_threshold_bytes;
            if combined_n > self.superfile_list.options.target_superfiles_per_part
                || latest_at_size_cap
            {
                // Split: keep the existing part, emit a fresh part for the new
                // superfiles.
                out_list_entries.push(entry.clone());
                let (fresh_entry, fresh_encoded_part) =
                    rebuild_part_and_entry(vec![], new_for_part, None, hidden_table);
                out_list_entries.push(fresh_entry);
                parts_to_write.push(fresh_encoded_part);
            } else {
                // Rewrite the latest part = its existing superfiles + the new.
                let existing_part = self.get_part_by_id(entry.part_id).await?;
                let (rebuilt_entry, rebuilt_encoded_part) = rebuild_part_and_entry(
                    existing_part.superfiles.clone(),
                    new_for_part,
                    Some(entry),
                    hidden_table,
                );
                out_list_entries.push(rebuilt_entry);
                parts_to_write.push(rebuilt_encoded_part);
            }
        }

        // Cold start: no prior parts, so the new entries form the first part.
        if !pending_new.is_empty() {
            let (fresh_entry, fresh_encoded_part) =
                rebuild_part_and_entry(vec![], pending_new, None, hidden_table);
            out_list_entries.push(fresh_entry);
            parts_to_write.push(fresh_encoded_part);
        }

        // At this point, out_list_entries contains all new ManifestListEntries that will be written.
        // If these out_list_entries i.e Vec<ManifestPartEntry> cause new ManifestParts to be created, those
        // are stored in parts_to_write.

        let mut out_list_entries_after_removal = Vec::new();
        if entries_to_remove.is_empty() {
            out_list_entries_after_removal = out_list_entries;
        } else {
            // 4. Apply removals across every part: drop the removed superfile_ids
            //    wherever they live; a part with no match is left untouched.
            let removal_ids = entries_to_remove
                .iter()
                .map(|r| r.superfile_id)
                .collect::<HashSet<_>>();
            for entry in out_list_entries {
                // TODO: Handle merging 2 parts into one if their sum is within threshold

                // Fetch the part's current superfiles — from parts_to_write (freshly
                // rebuilt this commit) or the prior manifest.
                let (superfile_entries_in_part, existing_part_to_update) = if let Some(existing) =
                    parts_to_write
                        .iter_mut()
                        .find(|ep| ep.part.part_id == entry.part_id)
                {
                    (existing.part.superfiles.clone(), Some(existing))
                } else if let Ok(existing_part) = self.get_part_by_id(entry.part_id).await {
                    (existing_part.superfiles.clone(), None)
                } else {
                    return Err(ManifestError::UnknownPartId(entry.part_id));
                };
                let final_superfile_entries = superfile_entries_in_part
                    .iter()
                    .filter(|s| !removal_ids.contains(&s.superfile_id))
                    .cloned()
                    .collect::<Vec<_>>();

                // No superfile removed from this part → keep it unchanged.
                if final_superfile_entries.len() == superfile_entries_in_part.len() {
                    out_list_entries_after_removal.push(entry);
                    continue;
                }

                let (fresh_entry, fresh_encoded_part) =
                    rebuild_part_and_entry(vec![], final_superfile_entries, None, hidden_table);

                if let Some(existing) = existing_part_to_update {
                    *existing = fresh_encoded_part;
                } else {
                    parts_to_write.push(fresh_encoded_part);
                }

                out_list_entries_after_removal.push(fresh_entry);
            }
        }

        let ids_to_remove = entries_to_remove
            .iter()
            .map(|e| e.superfile_id)
            .collect::<HashSet<_>>();

        // Carry the tombstone-seq map forward, dropping entries for
        // superfiles this commit removes — their sidecars leave the
        // manifest with them.
        let mut tombstone_seqs = self
            .list
            .as_ref()
            .map(|list| list.tombstone_seqs.clone())
            .unwrap_or_default();
        tombstone_seqs.retain(|id, _| !ids_to_remove.contains(id));

        let opts_hash = options_hash::compute_options_hash(opts.as_ref(), &strategy);
        let vector_columns: Vec<list::VectorColumnInfo> = opts
            .vector_columns
            .iter()
            .map(|v| list::VectorColumnInfo {
                column: v.column.clone(),
                dim: v.dim,
                n_cent: v.n_cent,
                rot_seed: v.rot_seed,
                metric: format!("{:?}", v.metric).to_lowercase(),
            })
            .collect();
        let new_list = Manifest {
            // Carry/advance the hidden drain watermark via the stamp (the drain
            // sets it with `with_drained_ranges` in the same commit). Empty on
            // the user manifest.
            drained_ranges: self.get_drained_ranges(),
            tombstone_seqs,
            format_version: LIST_FORMAT_VERSION.into(),
            manifest_id: self.get_next_manifest_id(),
            options_hash: opts_hash,
            schema: Vec::new(),
            id_column: opts.id_column.clone(),
            fts_columns: opts
                .fts_columns
                .iter()
                .map(|f| list::FtsColumnInfo {
                    column: f.column.clone(),
                })
                .collect(),
            vector_columns: opts
                .vector_columns
                .iter()
                .map(|v| list::VectorColumnInfo {
                    column: v.column.clone(),
                    dim: v.dim,
                    n_cent: v.n_cent,
                    rot_seed: v.rot_seed,
                    metric: format!("{:?}", v.metric).to_lowercase(),
                })
                .collect(),
            partition_strategy: strategy,
            // Never stamp a sibling prefix onto a hidden VectorCell manifest:
            // the prefix is only ever resolved off the USER manifest to locate
            // the hidden index, and a hidden table claiming its own hidden
            // subtree would misroute maintenance/GC.
            vector_index_storage_prefix: if matches!(
                self.get_partition_strategy(),
                list::PartitionStrategy::VectorCell { .. }
            ) {
                None
            } else {
                self.stamp_vector_index_storage_prefix(&vector_columns)
            },
            global_vector_index: self.get_global_vector_index(),
            deleted_user_ids_inline: self
                .list
                .as_ref()
                .and_then(|l| l.deleted_user_ids_inline.clone()),
            // Slow-CAS section is deliberately NOT carried into the
            // successor: `update` is the membership-change path (its only
            // production caller is the commit attempt), and a membership
            // change invalidates the prior entry blob. The commit attempt
            // restamps a fresh blob onto this successor via
            // [`Self::with_slow_vector_state_ref`] before the list/pointer
            // CAS, so membership and the slow-state ref publish together.
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: out_list_entries_after_removal,
        };
        let mut new_superfile_list = self
            .get_all_superfiles()
            .iter()
            .chain(stamped_new_entries.iter())
            .map(Arc::clone)
            .collect::<Vec<_>>();
        new_superfile_list.retain(|e| !ids_to_remove.contains(&e.superfile_id));

        let new_superfile_list = SuperfileList {
            manifest_id: self.get_next_manifest_id(),
            options: self.get_opts(),
            superfiles: new_superfile_list,
            vector_index_storage_prefix: None,
        };
        let loader = opts.storage.as_ref().map(|storage| {
            Arc::new(ManifestPartLoader::new_with_cache(
                storage.clone(),
                &new_list,
                opts.manifest_disk_cache.clone(),
            ))
        });
        // Inherit only the cached parts the new list still
        // references — entries for rewritten/removed parts are
        // dropped rather than carried forward, so the in-memory
        // parts cache can't grow without bound across commits.
        // Surviving parts keep their warm cache entry (no refetch);
        // the freshly-written parts are seeded below.
        let live_part_ids: HashSet<_> = new_list.parts.iter().map(|e| e.part_id).collect();
        let parts = DashMap::new();
        for kv in self.parts.iter() {
            if live_part_ids.contains(kv.key()) {
                parts.insert(*kv.key(), kv.value().clone());
            }
        }
        for part in parts_to_write.iter() {
            let part = part.part.clone();
            parts.insert(
                part.part_id,
                Arc::new(OnceCell::new_with(Some(Arc::new(part)))),
            );
        }

        let new_manifest = ManifestSnapshot {
            superfile_list: new_superfile_list,
            list: Some(new_list),
            parts,
            loader,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        };

        Ok((new_manifest, parts_to_write))
    }
}

/// build one `ManifestPart` from `superfiles` + the
/// matching `ManifestPartEntry`. Encodes the part in both wire forms —
/// full (fp32 + slab) and routing-only (counts + slab) — content-hashes
/// each, and computes the list-level aggregate skip summaries that
/// `list_prune` reads at query time. Both encodings ship in the returned
/// [`EncodedPart`] so the commit PUTs them together; the entry carries
/// the sibling ref consumer opens select on.
/// If base_part is Some, the superfiles MUST only include the new superfiles to be added.
fn rebuild_part_and_entry(
    old_superfiles: Vec<Arc<SuperfileEntry>>,
    new_superfiles: Vec<Arc<SuperfileEntry>>,
    base_part: Option<&ManifestPartEntry>,
    hidden: bool,
) -> (ManifestPartEntry, EncodedPart) {
    // Hidden (VectorCell) manifests write parts in ROUTING wire form and
    // skip the sibling: their fp32 is stored once per generation in the
    // slow-CAS centroid section, and their entries hydrate stripped for
    // everyone — a full-form part would be a fourth fp32 copy nothing
    // reads. User manifests keep both forms: the full part is the fp32
    // store the first rescore hydrates from (3 GETs vs the measured
    // 848-GET per-superfile fan), the routing sibling is what serving
    // opens fetch. `hidden` comes from the caller's PERSISTED strategy
    // (`get_partition_strategy`), never re-derived from raw options: a
    // handle opened with mismatched options must not flip a user part to
    // routing-only wire (fp32 would be dropped durably, with no sibling).
    let aggregates = aggregates::compute(&new_superfiles, base_part);
    let superfiles = old_superfiles
        .into_iter()
        .chain(new_superfiles)
        .collect::<Vec<_>>();
    let part = ManifestPart {
        format_version: part::FORMAT_VERSION.into(),
        part_id: PartId::new_v4(),
        superfiles,
    };
    let primary_mode = if hidden {
        SummaryWireMode::RoutingOnly
    } else {
        SummaryWireMode::Full
    };
    let compressed = part::encode_with_mode(&part, primary_mode);
    let size_compressed = compressed.len() as u64;
    let content_hash = ContentHash::of(&compressed);
    let size_uncompressed = frame_content_size(&compressed, size_compressed);
    let routing = if hidden {
        None
    } else {
        let routing_encoded = part::encode_with_mode(&part, SummaryWireMode::RoutingOnly);
        let routing_hash = ContentHash::of(&routing_encoded);
        Some((routing_encoded, routing_hash))
    };
    let entry = ManifestPartEntry {
        part_id: part.part_id,
        uri: part_uri(&content_hash),
        n_superfiles: part.superfiles.len() as u64,
        size_bytes_compressed: size_compressed,
        size_bytes_uncompressed: size_uncompressed,
        content_hash,
        routing: routing.as_ref().map(|(_, hash)| RoutingRef {
            uri: part_uri(hash),
            content_hash: *hash,
        }),
        id_range: aggregates.id_range,
        scalar_stats_agg: aggregates.scalar_stats_agg,
        fts_summary_agg: aggregates.fts_summary_agg,
    };
    (
        entry,
        EncodedPart {
            part,
            encoded: compressed,
            routing_encoded: routing.map(|(bytes, _)| bytes),
        },
    )
}

/// Pulls manifest parts through a [`StorageProvider`] and verifies
/// content-hash on load.
///
/// One `ManifestPartLoader` per `ManifestSnapshot`. The same `Arc<dyn
/// StorageProvider>` is shared with the `DiskCacheStore` —
/// one auth handshake, one connection pool.
///
/// An optional [`ManifestDiskCache`] short-circuits the storage GET
/// when the part's compressed bytes are already on local disk. Because
/// parts are content-addressed, a cache hit can never be stale.
pub struct ManifestPartLoader {
    storage: Arc<dyn StorageProvider>,
    /// Maps `PartId → (expected content_hash, uri, routing sibling)`.
    /// Built from the manifest list at construction; immutable
    /// per-`ManifestSnapshot`.
    parts_index: HashMap<PartId, (ContentHash, String, Option<RoutingRef>)>,
    /// On-disk cache for compressed part bytes. `None` disables the
    /// cache (in-process-only supertables, tests, or storage attached
    /// without a `disk_cache_root` configured).
    manifest_disk_cache: Option<Arc<ManifestDiskCache>>,
    /// Consumer memory mode (`summary_centroids_from_superfiles`): load
    /// each part's routing sibling (counts + 1-bit slab, no fp32) when
    /// the list stamps one. Writer handles keep this off — part rebuilds
    /// re-encode the full form and need resident fp32.
    prefer_routing: bool,
}

impl ManifestPartLoader {
    pub fn new(storage: Arc<dyn StorageProvider>, list: &Manifest) -> Self {
        Self::new_with_cache(storage, list, None)
    }

    /// Like [`Self::new`] but attaches an on-disk part-bytes cache.
    pub fn new_with_cache(
        storage: Arc<dyn StorageProvider>,
        list: &Manifest,
        manifest_disk_cache: Option<Arc<ManifestDiskCache>>,
    ) -> Self {
        Self::new_with_cache_and_mode(storage, list, manifest_disk_cache, false)
    }

    /// Like [`Self::new_with_cache`] with the consumer routing mode
    /// explicit — `prefer_routing` selects each part's routing sibling
    /// when present.
    pub fn new_with_cache_and_mode(
        storage: Arc<dyn StorageProvider>,
        list: &Manifest,
        manifest_disk_cache: Option<Arc<ManifestDiskCache>>,
        prefer_routing: bool,
    ) -> Self {
        let mut idx = HashMap::with_capacity(list.parts.len());
        for entry in &list.parts {
            idx.insert(
                entry.part_id,
                (entry.content_hash, entry.uri.clone(), entry.routing.clone()),
            );
        }
        Self {
            storage,
            parts_index: idx,
            manifest_disk_cache,
            prefer_routing,
        }
    }

    /// Fetch + verify + decode one part. Returns the parsed
    /// `Arc<ManifestPart>`.
    ///
    /// Consults the on-disk cache first (a hit skips the storage GET);
    /// on a miss the freshly-fetched bytes are written back to the
    /// cache (best-effort) before decoding.
    pub async fn load(&self, part_id: PartId) -> Result<Arc<ManifestPart>, ManifestLoadError> {
        self.load_with_form(part_id, self.prefer_routing).await
    }

    /// [`Self::load`] forced to the FULL wire form (fp32 summaries intact)
    /// regardless of the loader's routing preference — the user-table
    /// centroid hydration reads full parts once even on consumers that
    /// open with routing siblings.
    pub async fn load_full(&self, part_id: PartId) -> Result<Arc<ManifestPart>, ManifestLoadError> {
        self.load_with_form(part_id, false).await
    }

    async fn load_with_form(
        &self,
        part_id: PartId,
        prefer_routing: bool,
    ) -> Result<Arc<ManifestPart>, ManifestLoadError> {
        let (full_hash, full_uri, routing) = self
            .parts_index
            .get(&part_id)
            .ok_or(ManifestLoadError::PartNotInList { part_id })?;
        // Routing decode lands in the stripped in-memory shape; both forms
        // are content-addressed, so the disk cache can never mix them.
        let (expected_hash, uri) = match (prefer_routing, routing) {
            (true, Some(routing)) => (&routing.content_hash, &routing.uri),
            _ => (full_hash, full_uri),
        };

        // Disk-cache hit: bytes are verified against `expected_hash`
        // inside `get`, so they're known-good here.
        if let Some(cache) = &self.manifest_disk_cache
            && let Some(bytes) = cache.get(expected_hash).await
        {
            let parsed = decode_part_off_thread(Bytes::from(bytes)).await?;
            return Ok(Arc::new(parsed));
        }

        let (bytes, _) = self
            .storage
            .get(uri)
            .await
            .map_err(ManifestLoadError::Storage)?;
        // Hash verify runs inside the same blocking task as the decode:
        // blake3 over a multi-hundred-MiB part is CPU the polling task
        // must not absorb (it serializes the nominally-concurrent part
        // fan exactly like the inline decode used to).
        let parsed = verify_and_decode_part_off_thread(bytes.clone(), *expected_hash).await?;
        // Populate the cache for next time (best-effort; the hash was
        // verified above, satisfying `put`'s contract).
        if let Some(cache) = &self.manifest_disk_cache {
            cache.put(*expected_hash, &bytes).await;
        }
        Ok(Arc::new(parsed))
    }
}

/// One consumer's hydrated user-table fp32 fine centroids, built once per
/// manifest generation from the FULL manifest parts (the user table's
/// content-addressed store for summary fp32 — the slow-CAS analog). Keyed
/// by `manifest_id`; a membership change rebuilds it on the next rescore.
/// Resident by design: user summaries are per-fragment cells (~100 MB at
/// 100M docs), unlike the hidden table's fine fp32 (spilled section).
pub(crate) struct UserCentroidCache {
    pub(crate) manifest_id: u64,
    /// `(superfile_id, column)` → per-cell `(cell_id, fp32 centroids)`.
    pub(crate) cells: HashMap<(Uuid, String), Vec<(Option<u32>, Arc<Vec<f32>>)>>,
}

impl UserCentroidCache {
    /// One cell's fp32 fine centroids, when the cache carries them.
    pub(crate) fn cell(
        &self,
        superfile_id: Uuid,
        column: &str,
        cell_id: Option<u32>,
    ) -> Option<Arc<Vec<f32>>> {
        self.cells
            .get(&(superfile_id, column.to_owned()))?
            .iter()
            .find(|(id, _)| *id == cell_id)
            .map(|(_, fp32)| Arc::clone(fp32))
    }

    /// Build from fully-loaded parts: every entry's summary cells that
    /// carry resident fp32.
    pub(crate) fn from_parts(manifest_id: u64, parts: &[Arc<ManifestPart>]) -> Self {
        let mut cells: HashMap<(Uuid, String), Vec<(Option<u32>, Arc<Vec<f32>>)>> = HashMap::new();
        for part in parts {
            for entry in &part.superfiles {
                for (column, summary) in &entry.vector_summary {
                    let list = cells
                        .entry((entry.superfile_id, column.clone()))
                        .or_default();
                    for cell in &summary.cells {
                        if cell.clusters.vectors_resident() && cell.clusters.n_cent > 0 {
                            list.push((cell.cell_id, Arc::new(cell.clusters.centroids.clone())));
                        }
                    }
                }
            }
        }
        Self { manifest_id, cells }
    }
}

/// Decode part bytes off the async runtime. Part decode is a CPU wave
/// (multi-MiB Avro payloads carrying centroid summaries and open blobs);
/// running it inline used to serialize every part behind one polling
/// task, so 18 nominally-concurrent part loads decoded one at a time.
/// `spawn_blocking` keeps the runtime free to drive the remaining
/// fetches while decodes run in parallel on the blocking pool.
async fn decode_part_off_thread(bytes: Bytes) -> Result<ManifestPart, ManifestLoadError> {
    match spawn_blocking(move || part::decode(&bytes)).await {
        Ok(result) => Ok(result?),
        Err(join_error) => Err(ManifestLoadError::Parse(part::PartParseError::Avro(
            format!("part decode task failed: {join_error}"),
        ))),
    }
}

/// [`decode_part_off_thread`] preceded by a blake3 content-hash check on
/// the same blocking task, for the storage-GET path where the bytes are
/// not yet verified.
async fn verify_and_decode_part_off_thread(
    bytes: Bytes,
    expected_hash: ContentHash,
) -> Result<ManifestPart, ManifestLoadError> {
    let verify_then_decode = move || {
        let actual_hash = ContentHash::of(&bytes);
        if actual_hash != expected_hash {
            return Err(ManifestLoadError::ContentHashMismatch {
                expected: expected_hash.to_hex(),
                actual: actual_hash.to_hex(),
            });
        }
        part::decode(&bytes).map_err(ManifestLoadError::from)
    };
    match spawn_blocking(verify_then_decode).await {
        Ok(result) => result,
        Err(join_error) => Err(ManifestLoadError::Parse(part::PartParseError::Avro(
            format!("part verify/decode task failed: {join_error}"),
        ))),
    }
}

/// Errors raised by [`ManifestSnapshot::part`] and [`ManifestPartLoader::load`].
///
/// Standalone (not folded into the supertable-level
/// `OpenError`) so the per-part load surface stays narrowly
/// testable in isolation.
#[derive(Debug, thiserror::Error)]
pub enum ManifestLoadError {
    /// Pointer not found in storage.
    #[error("pointer not found in storage")]
    PointerNotFound,
    #[error("already loaded")]
    AlreadyLoaded,
    /// Pointer parse error.
    #[error("pointer parse error: {0}")]
    PointerParse(String),
    /// Caller invoked `ManifestSnapshot::part(...)` on an in-process-only
    /// manifest (no storage attached). The hierarchical manifest
    /// has no on-disk parts to load from.
    #[error("no storage / loader attached to this manifest")]
    NoLoaderAttached,

    #[error("list parse error: {0}")]
    ListParse(#[source] list::ListParseError),
    /// `part_id` isn't in this manifest's list. Either the caller
    /// passed a stale id (pre-refresh) or the manifest list is
    /// missing an entry.
    #[error("part_id not in manifest list: {part_id}")]
    PartNotInList { part_id: PartId },
    /// Storage backend returned an error.
    #[error("storage error during part load: {0}")]
    Storage(#[source] StorageError),
    /// Computed blake3 of the loaded bytes didn't match the
    /// manifest list's recorded `content_hash`. The bad bytes
    /// are **not** auto-refetched — a mismatch indicates
    /// corruption, not a transient race, so it's surfaced as
    /// a caller-visible failure rather than papered over.
    #[error("content-hash mismatch: expected {expected}, got {actual}")]
    ContentHashMismatch { expected: String, actual: String },
    /// Avro / zstd / version-incompat parse failure.
    #[error("part parse failed")]
    Parse(#[from] part::PartParseError),
    /// Slow-state blob hydration failed while the list carries a ref —
    /// missing object, hash mismatch, decode failure, or an entry count
    /// that disagrees with the list. Corruption, not a race: surfaced as
    /// a load failure rather than silently degrading to the part fan (a
    /// quiet fallback here concealed real defects across whole bench
    /// cycles).
    #[error("slow vector-state hydration failed: {0}")]
    SlowStateHydration(String),
}

/// One superfile's metadata + skip-pruning summaries. The bytes that
/// back the superfile live in the superfile store keyed by `uri` —
/// `superfile_id` is for debugging / observability, `uri` is for
/// store routing.
#[derive(Debug, Clone)]
pub struct SuperfileEntry {
    /// Globally unique identifier (UUID v4) for debugging /
    /// observability. Distinct from `uri` so the store routing key
    /// can evolve independently of identity.
    pub superfile_id: Uuid,
    /// Opaque key into the `SuperfileReaderCache`. v1 wraps a UUID; the
    /// trait doesn't care about the internal shape.
    pub uri: SuperfileUri,
    /// Row count.
    pub n_docs: u64,
    /// id-column min and max (the supertable-injected
    /// `Decimal128(38, 0)` id column). Stored as `i128` to
    /// carry the 128-bit Snowflake-shaped values produced by
    /// the supertable's `IdGenerator`. Signed-int comparison
    /// gives time-ordered skip-pruning because the high bit
    /// stays 0 for any plausible current-era timestamp.
    pub id_min: i128,
    pub id_max: i128,
    /// Per-scalar-column aggregate (min/max + null count, exact sum, HLL),
    /// keyed by column name, for skip pruning of SQL filters. An absent
    /// column means "no usable stats" (the pruner keeps the superfile).
    pub scalar_stats: HashMap<String, ScalarStatsAgg>,
    /// Per-FTS-column term-presence bloom + lex range. The bloom
    /// drives exact-term skip; the term-range drives prefix-query
    /// skip via `[prefix, prefix_upper_bound)` overlap. Keyed by
    /// FTS column name. Same per-column [`FtsSummaryAgg`] shape the
    /// list-level aggregate uses; built per superfile via
    /// [`FtsSummaryAgg::from_superfile`].
    pub fts_summary: HashMap<String, FtsSummaryAgg>,
    /// Per-vector-column summary centroid + per-cluster IVF centroids,
    /// driving global cluster selection at query time. Keyed by vector
    /// column name.
    pub vector_summary: HashMap<String, VectorSummary>,
    /// Partition assignment, encoded opaquely per the strategy
    /// (time_range = 8-byte LE u64 bucket index; hash = 4-byte LE
    /// u32 bucket id; column_range = 2-byte LE u16 boundary index).
    /// Empty (decoded as "unpartitioned") when no real partition
    /// strategy is configured; otherwise filled by the writer
    /// from the configured strategy at commit time.
    pub partition_key: Vec<u8>,
    /// Hash partitioning operates per-row, but at commit time we
    /// only have per-superfile summaries. Hash strategy requires
    /// superfiles to be pre-sharded — each builder-shard stamps the
    /// resulting bucket here on ingest. `None` under non-hash
    /// strategies and under the single-bucket Hash default.
    pub partition_hint: Option<u32>,
    /// precomputed superfile layout offsets so the
    /// cold-open path can fire the parquet-footer, vector
    /// subsection, and FTS subsection GETs **in parallel** in a
    /// single round-trip, without first reading the parquet KV
    /// metadata to learn where each subsection lives.
    ///
    /// Populated by the writer at commit time from the
    /// `ParquetParts` returned by `splice_index_blobs` (so
    /// the values are by construction consistent with what the
    /// parquet KV metadata would later say).
    ///
    /// `None` on superfiles produced by older writers that did not
    /// stamp this field; the cold open path falls back to the
    /// 2-RTT shape (parquet tail
    /// then vec/fts in parallel) — see
    /// `DiskCacheStore::reader_with_hints`.
    pub subsection_offsets: Option<SubsectionOffsets>,
    pub(crate) vector_layout: VectorLayout,
    /// The `manifest_id` of the commit that introduced this superfile — its
    /// **birth version**. Stamped in [`ManifestSnapshot::update`] for newly-added
    /// entries (re-derived per OCC attempt, so it always equals the winning
    /// commit's version); carried over unchanged for entries that survive a
    /// commit. The hidden-index drain uses it to track which user commits it
    /// has consumed into cells (see the hidden manifest's `drained_ranges`):
    /// because the manifest-pointer CAS serializes every commit across all
    /// writers/hosts into one gap-free version sequence, this is the only
    /// total order that's safe to watermark on. `0` on entries from before
    /// the field existed (treated as the genesis version).
    pub birth_version: u64,
}

/// superfile layout offsets cached on the manifest.
///
/// Knowing these up-front lets the cold-open path issue every
/// subsection GET in parallel against the same superfile object,
/// turning the canonical 2-RTT cold open (parquet tail → vec+fts
/// in parallel) into a single round-trip.
///
/// All offsets are absolute byte positions within the superfile
/// blob (matching `inf.vec.offset` / `inf.fts.offset` parquet KV
/// values), and `total_size` matches what an S3 `HEAD` would
/// return.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SubsectionOffsets {
    /// Total byte count of the superfile blob. Lets the cold-open
    /// path skip the upfront `HEAD` round-trip too — the same
    /// information the suffix-range tail would otherwise return,
    /// but available without any I/O.
    pub total_size: u64,
    /// Absolute `(offset, length)` of the vector subsection. `None`
    /// when the superfile carries no vector subsection.
    pub vec: Option<(u64, u64)>,
    /// Absolute `(offset, length)` of the FTS subsection. `None`
    /// when the superfile carries no FTS subsection.
    pub fts: Option<(u64, u64)>,
    /// Absolute ranges that fully cover vector open-time metadata.
    /// The hinted cache path prefetches these in the first network
    /// batch so `VectorReader::open_lazy` can resolve header,
    /// directory, subheaders, and codec metadata from the overlay.
    pub vec_open_ranges: Vec<(u64, u64)>,
    /// Absolute ranges that fully cover FTS open-time metadata:
    /// header+dictionary and doc-length tables. Query-time postings
    /// stay lazy.
    pub fts_open_ranges: Vec<(u64, u64)>,
    /// the actual bytes covering the superfile's
    /// open-time batch (parquet footer tail + the
    /// `vec_open_ranges` + the `fts_open_ranges`), carried inline
    /// in the manifest part.
    ///
    /// When non-empty, the cold-fetch path installs these directly
    /// into the reader's prefetch overlay and issues **zero**
    /// open-time GETs against the superfile object — the bytes
    /// already arrived in the single part GET that `cold_open`
    /// performs. The genuine first-touch per-superfile cost then
    /// collapses from 2 RTT-batches (open metadata + cluster
    /// postings) to 1 (postings only).
    ///
    /// Each tuple is `(absolute_offset, bytes)`. Empty on superfiles
    /// produced by older writers that did not capture it, or when
    /// blob capture is disabled
    /// — the path then falls back to fetching `vec_open_ranges` /
    /// `fts_open_ranges` over the wire.
    pub open_blob: Vec<(u64, Vec<u8>)>,
}

/// Opaque store key — wraps a UUID v4. The superfile store treats
/// this as a hash-eq token and doesn't peek inside. An
/// object-store-backed variant could swap to a path-shaped URI
/// without changing any caller, since the trait shape stays the
/// same.
#[derive(Clone, Copy, Hash, Eq, PartialEq, Ord, PartialOrd, Debug)]
pub struct SuperfileUri(pub Uuid);

impl SuperfileUri {
    /// Generate a fresh URI. Called by the writer at commit time
    /// when assigning a key for a new superfile's bytes.
    pub fn new_v4() -> Self {
        Self(Uuid::new_v4())
    }

    /// Object-store / LocalFS path for committed superfile bytes.
    /// `.sf.parquet` double suffix — on disk this is still valid
    /// Parquet (row groups + optional embedded FTS/vector blobs +
    /// footer), while the `.sf` marker flags it as a Superfile
    /// superfile without making the file look non-standard.
    pub fn storage_path(self) -> String {
        format!("{SUPERFILE_DATA_DIR}/seg-{}.sf.parquet", self.0)
    }

    /// Disk-cache filename for a promoted superfile.
    pub fn cache_filename(self) -> String {
        format!("seg-{}.sf.parquet", self.0)
    }

    /// Disk-cache tempfile while a cold fetch is in flight.
    pub fn cache_tmp_filename(self) -> String {
        format!("seg-{}.sf.parquet.tmp", self.0)
    }

    /// Inverse of [`Self::cache_filename`]: recover the URI from an on-disk
    /// cache file name. The disk cache uses this to rebuild its in-memory index
    /// from files a prior run left under `cache_root`, so a restart / second
    /// handle reuses the NVMe bytes instead of cold-fetching from object
    /// storage. Returns `None` for anything that isn't exactly
    /// `seg-<uuid>.sf.parquet` — notably the `.tmp` in-flight files, whose
    /// longer `.sf.parquet.tmp` suffix must be ignored (incomplete writes).
    pub fn from_cache_filename(name: &str) -> Option<Self> {
        let body = name.strip_prefix("seg-")?.strip_suffix(".sf.parquet")?;
        Uuid::parse_str(body).ok().map(SuperfileUri)
    }
}

/// Merge min/max arrays by comparing values and keeping the actual min and max.
///
/// Takes existing (min, max) and other (min, max) arrays and returns the
/// merged (min, max) where min is the smaller value and max is the larger.
/// Both arrays are assumed to be length-1 and of the same type.
pub(crate) fn merge_min_max_arrays(
    existing_min: &ArrayRef,
    other_min: &ArrayRef,
    existing_max: &ArrayRef,
    other_max: &ArrayRef,
) -> Option<(ArrayRef, ArrayRef)> {
    // Merge two optional bounds into the surviving one — smaller for a min,
    // larger for a max. A `None` (the column is all-null on that side)
    // yields to a present value; both `None` stays `None`, so an all-null
    // column stays all-null through the fold, while a manifest part with any
    // populated superfile keeps its real bound.
    #[inline]
    fn merge_opt<T: PartialOrd>(a: Option<T>, b: Option<T>, keep_min: bool) -> Option<T> {
        match (a, b) {
            (Some(a), Some(b)) => Some(if keep_min == (a <= b) { a } else { b }),
            (Some(v), None) | (None, Some(v)) => Some(v),
            (None, None) => None,
        }
    }

    macro_rules! prim_merge {
        ($array_ty:ty) => {{
            let exn = existing_min.as_any().downcast_ref::<$array_ty>()?;
            let otn = other_min.as_any().downcast_ref::<$array_ty>()?;
            let exx = existing_max.as_any().downcast_ref::<$array_ty>()?;
            let otx = other_max.as_any().downcast_ref::<$array_ty>()?;
            let at = |a: &$array_ty| (!a.is_null(0)).then(|| a.value(0));
            Some((
                Arc::new(<$array_ty>::from(vec![merge_opt(at(exn), at(otn), true)])) as ArrayRef,
                Arc::new(<$array_ty>::from(vec![merge_opt(at(exx), at(otx), false)])) as ArrayRef,
            ))
        }};
    }

    // Same fold, re-attaching the column's timezone (the constructor drops
    // it) so the merged bound keeps the exact type its inputs carried.
    macro_rules! ts_merge {
        ($array_ty:ty, $tz:expr) => {{
            let exn = existing_min.as_any().downcast_ref::<$array_ty>()?;
            let otn = other_min.as_any().downcast_ref::<$array_ty>()?;
            let exx = existing_max.as_any().downcast_ref::<$array_ty>()?;
            let otx = other_max.as_any().downcast_ref::<$array_ty>()?;
            let at = |a: &$array_ty| (!a.is_null(0)).then(|| a.value(0));
            Some((
                Arc::new(
                    <$array_ty>::from(vec![merge_opt(at(exn), at(otn), true)])
                        .with_timezone_opt($tz.clone()),
                ) as ArrayRef,
                Arc::new(
                    <$array_ty>::from(vec![merge_opt(at(exx), at(otx), false)])
                        .with_timezone_opt($tz.clone()),
                ) as ArrayRef,
            ))
        }};
    }

    match existing_min.data_type() {
        DataType::UInt8 => prim_merge!(UInt8Array),
        DataType::UInt16 => prim_merge!(UInt16Array),
        DataType::UInt32 => prim_merge!(UInt32Array),
        DataType::UInt64 => prim_merge!(UInt64Array),
        DataType::Int8 => prim_merge!(Int8Array),
        DataType::Int16 => prim_merge!(Int16Array),
        DataType::Int32 => prim_merge!(Int32Array),
        DataType::Int64 => prim_merge!(Int64Array),
        DataType::Float32 => prim_merge!(Float32Array),
        DataType::Float64 => prim_merge!(Float64Array),
        // `false < true`, so min folds like AND and max like OR.
        DataType::Boolean => prim_merge!(BooleanArray),
        DataType::Utf8 => {
            let exn = existing_min.as_any().downcast_ref::<StringArray>()?;
            let otn = other_min.as_any().downcast_ref::<StringArray>()?;
            let exx = existing_max.as_any().downcast_ref::<StringArray>()?;
            let otx = other_max.as_any().downcast_ref::<StringArray>()?;
            let min = merge_opt(
                (!exn.is_null(0)).then(|| exn.value(0)),
                (!otn.is_null(0)).then(|| otn.value(0)),
                true,
            );
            let max = merge_opt(
                (!exx.is_null(0)).then(|| exx.value(0)),
                (!otx.is_null(0)).then(|| otx.value(0)),
                false,
            );
            Some((
                Arc::new(StringArray::from(vec![min])),
                Arc::new(StringArray::from(vec![max])),
            ))
        }
        DataType::LargeUtf8 => {
            let exn = existing_min.as_any().downcast_ref::<LargeStringArray>()?;
            let otn = other_min.as_any().downcast_ref::<LargeStringArray>()?;
            let exx = existing_max.as_any().downcast_ref::<LargeStringArray>()?;
            let otx = other_max.as_any().downcast_ref::<LargeStringArray>()?;
            let min = merge_opt(
                (!exn.is_null(0)).then(|| exn.value(0)),
                (!otn.is_null(0)).then(|| otn.value(0)),
                true,
            );
            let max = merge_opt(
                (!exx.is_null(0)).then(|| exx.value(0)),
                (!otx.is_null(0)).then(|| otx.value(0)),
                false,
            );
            Some((
                Arc::new(LargeStringArray::from(vec![min])),
                Arc::new(LargeStringArray::from(vec![max])),
            ))
        }
        DataType::Decimal128(precision, scale) => {
            let exn = existing_min.as_any().downcast_ref::<Decimal128Array>()?;
            let otn = other_min.as_any().downcast_ref::<Decimal128Array>()?;
            let exx = existing_max.as_any().downcast_ref::<Decimal128Array>()?;
            let otx = other_max.as_any().downcast_ref::<Decimal128Array>()?;
            let at = |a: &Decimal128Array| (!a.is_null(0)).then(|| a.value(0));
            let min = merge_opt(at(exn), at(otn), true);
            let max = merge_opt(at(exx), at(otx), false);
            Some((
                Arc::new(
                    Decimal128Array::from(vec![min])
                        .with_precision_and_scale(*precision, *scale)
                        .ok()?,
                ),
                Arc::new(
                    Decimal128Array::from(vec![max])
                        .with_precision_and_scale(*precision, *scale)
                        .ok()?,
                ),
            ))
        }

        // Mirror `column_min_max`'s temporal set; without these arms a
        // multi-superfile (or compacted) temporal column errors the merge and
        // drops its stat, silently regressing the fold and range prune.
        DataType::Date32 => prim_merge!(Date32Array),
        DataType::Date64 => prim_merge!(Date64Array),
        DataType::Time32(TimeUnit::Second) => prim_merge!(Time32SecondArray),
        DataType::Time32(TimeUnit::Millisecond) => prim_merge!(Time32MillisecondArray),
        DataType::Time64(TimeUnit::Microsecond) => prim_merge!(Time64MicrosecondArray),
        DataType::Time64(TimeUnit::Nanosecond) => prim_merge!(Time64NanosecondArray),
        DataType::Timestamp(TimeUnit::Second, tz) => ts_merge!(TimestampSecondArray, tz),
        DataType::Timestamp(TimeUnit::Millisecond, tz) => ts_merge!(TimestampMillisecondArray, tz),
        DataType::Timestamp(TimeUnit::Microsecond, tz) => ts_merge!(TimestampMicrosecondArray, tz),
        DataType::Timestamp(TimeUnit::Nanosecond, tz) => ts_merge!(TimestampNanosecondArray, tz),
        _ => None,
    }
}

/// Compute (min, max) for one Arrow array as length-1 `ArrayRef`s.
///
/// Returns `None` only for unsupported types. An all-null input of a
/// supported type yields length-1 *null* min/max arrays (not `None`), so
/// its null count is still recorded and `IS [NOT] NULL` can prune on it.
/// Supported set: integer (signed + unsigned, all widths), float
/// (f32, f64), boolean, Utf8, LargeUtf8, Decimal128, and temporal
/// (Date32/64, Time32/64, Timestamp). The supertable schema
/// rejects vector columns up at the SupertableOptions layer, so
/// `FixedSizeList<Float32>` won't appear here in practice.
/// Exact column sum as a length-1 array typed to match SQL `SUM`'s
/// result for the column (signed → `Int64`, unsigned → `UInt64`,
/// floats → `Float64`). `None` for non-summable types (utf8, bool,
/// decimal) or when the exact total overflows the result type —
/// consumers treat missing as "no statistics".
pub(crate) fn column_sum(col: &ArrayRef) -> Option<ArrayRef> {
    macro_rules! signed {
        ($array_ty:ty) => {{
            let a = col.as_any().downcast_ref::<$array_ty>()?;
            let total: i128 = a.iter().flatten().map(i128::from).sum();
            let v = i64::try_from(total).ok()?;
            Some(Arc::new(Int64Array::from(vec![v])) as ArrayRef)
        }};
    }
    macro_rules! unsigned {
        ($array_ty:ty) => {{
            let a = col.as_any().downcast_ref::<$array_ty>()?;
            let total: u128 = a.iter().flatten().map(u128::from).sum();
            let v = u64::try_from(total).ok()?;
            Some(Arc::new(UInt64Array::from(vec![v])) as ArrayRef)
        }};
    }
    macro_rules! float {
        ($array_ty:ty) => {{
            let a = col.as_any().downcast_ref::<$array_ty>()?;
            let total: f64 = a.iter().flatten().map(f64::from).sum();
            Some(Arc::new(Float64Array::from(vec![total])) as ArrayRef)
        }};
    }

    match col.data_type() {
        DataType::Int8 => signed!(Int8Array),
        DataType::Int16 => signed!(Int16Array),
        DataType::Int32 => signed!(Int32Array),
        DataType::Int64 => signed!(Int64Array),
        DataType::UInt8 => unsigned!(UInt8Array),
        DataType::UInt16 => unsigned!(UInt16Array),
        DataType::UInt32 => unsigned!(UInt32Array),
        DataType::UInt64 => unsigned!(UInt64Array),
        DataType::Float32 => float!(Float32Array),
        DataType::Float64 => float!(Float64Array),
        _ => None,
    }
}

/// Add two length-1 sum arrays of the same type (see [`column_sum`]).
/// `None` on type mismatch or `Int64`/`UInt64` overflow. Shared with
/// the SQL provider's cross-segment statistics fold.
pub(crate) fn add_sum_arrays(a: &ArrayRef, b: &ArrayRef) -> Option<ArrayRef> {
    match (a.data_type(), b.data_type()) {
        (DataType::Int64, DataType::Int64) => {
            let x = a.as_any().downcast_ref::<Int64Array>()?.value(0);
            let y = b.as_any().downcast_ref::<Int64Array>()?.value(0);
            Some(Arc::new(Int64Array::from(vec![x.checked_add(y)?])) as ArrayRef)
        }
        (DataType::UInt64, DataType::UInt64) => {
            let x = a.as_any().downcast_ref::<UInt64Array>()?.value(0);
            let y = b.as_any().downcast_ref::<UInt64Array>()?.value(0);
            Some(Arc::new(UInt64Array::from(vec![x.checked_add(y)?])) as ArrayRef)
        }
        (DataType::Float64, DataType::Float64) => {
            let x = a.as_any().downcast_ref::<Float64Array>()?.value(0);
            let y = b.as_any().downcast_ref::<Float64Array>()?.value(0);
            Some(Arc::new(Float64Array::from(vec![x + y])) as ArrayRef)
        }
        _ => None,
    }
}

/// HyperLogLog distinct sketch over a column's non-null values.
/// `None` for types the sketch doesn't cover. Values hash by their
/// canonical byte representation (little-endian for numerics, raw
/// bytes for strings, IEEE bits for floats).
pub(crate) fn column_hll(col: &ArrayRef) -> Option<hll::HllSketch> {
    let mut sketch = hll::HllSketch::new();
    macro_rules! ints {
        ($array_ty:ty) => {{
            let a = col.as_any().downcast_ref::<$array_ty>()?;
            for v in a.iter().flatten() {
                sketch.insert_hash(xxh3_64(&v.to_le_bytes()));
            }
        }};
    }
    match col.data_type() {
        DataType::Int8 => ints!(Int8Array),
        DataType::Int16 => ints!(Int16Array),
        DataType::Int32 => ints!(Int32Array),
        DataType::Int64 => ints!(Int64Array),
        DataType::UInt8 => ints!(UInt8Array),
        DataType::UInt16 => ints!(UInt16Array),
        DataType::UInt32 => ints!(UInt32Array),
        DataType::UInt64 => ints!(UInt64Array),
        DataType::Float32 => {
            let a = col.as_any().downcast_ref::<Float32Array>()?;
            for v in a.iter().flatten() {
                sketch.insert_hash(xxh3_64(&v.to_bits().to_le_bytes()));
            }
        }
        DataType::Float64 => {
            let a = col.as_any().downcast_ref::<Float64Array>()?;
            for v in a.iter().flatten() {
                sketch.insert_hash(xxh3_64(&v.to_bits().to_le_bytes()));
            }
        }
        DataType::Utf8 => {
            let a = col.as_any().downcast_ref::<StringArray>()?;
            for v in a.iter().flatten() {
                sketch.insert_hash(xxh3_64(v.as_bytes()));
            }
        }
        DataType::LargeUtf8 => {
            let a = col.as_any().downcast_ref::<LargeStringArray>()?;
            for v in a.iter().flatten() {
                sketch.insert_hash(xxh3_64(v.as_bytes()));
            }
        }
        _ => return None,
    }
    Some(sketch)
}

pub(crate) fn column_min_max(col: &ArrayRef) -> Option<(ArrayRef, ArrayRef)> {
    // An all-null column yields *null* min/max (not no-stat), so its null
    // count is still recorded for `IS [NOT] NULL` pruning — hence the
    // `Option` min/max are kept rather than `?`-unwrapped away.
    macro_rules! prim {
        ($array_ty:ty) => {{
            let a = col.as_any().downcast_ref::<$array_ty>()?;
            let mn_arr: ArrayRef = Arc::new(<$array_ty>::from(vec![agg::min(a)]));
            let mx_arr: ArrayRef = Arc::new(<$array_ty>::from(vec![agg::max(a)]));
            Some((mn_arr, mx_arr))
        }};
    }

    // Timestamps are the same primitive fold, but the `from(vec![..])`
    // constructor builds a zone-less array; re-attach the column's zone so
    // the bound keeps its exact type (a naive-vs-zoned mismatch would fail
    // the cross-superfile merge and stat reconstruction).
    macro_rules! ts {
        ($array_ty:ty, $tz:expr) => {{
            let a = col.as_any().downcast_ref::<$array_ty>()?;
            let mn_arr: ArrayRef =
                Arc::new(<$array_ty>::from(vec![agg::min(a)]).with_timezone_opt($tz.clone()));
            let mx_arr: ArrayRef =
                Arc::new(<$array_ty>::from(vec![agg::max(a)]).with_timezone_opt($tz.clone()));
            Some((mn_arr, mx_arr))
        }};
    }

    match col.data_type() {
        DataType::UInt8 => prim!(UInt8Array),
        DataType::UInt16 => prim!(UInt16Array),
        DataType::UInt32 => prim!(UInt32Array),
        DataType::UInt64 => prim!(UInt64Array),
        DataType::Int8 => prim!(Int8Array),
        DataType::Int16 => prim!(Int16Array),
        DataType::Int32 => prim!(Int32Array),
        DataType::Int64 => prim!(Int64Array),
        DataType::Float32 => prim!(Float32Array),
        DataType::Float64 => prim!(Float64Array),
        DataType::Boolean => {
            let a = col.as_any().downcast_ref::<BooleanArray>()?;
            Some((
                Arc::new(BooleanArray::from(vec![agg::min_boolean(a)])),
                Arc::new(BooleanArray::from(vec![agg::max_boolean(a)])),
            ))
        }
        DataType::Utf8 => {
            let a = col.as_any().downcast_ref::<StringArray>()?;
            Some((
                Arc::new(StringArray::from(vec![agg::min_string(a)])),
                Arc::new(StringArray::from(vec![agg::max_string(a)])),
            ))
        }
        DataType::LargeUtf8 => {
            let a = col.as_any().downcast_ref::<LargeStringArray>()?;
            Some((
                Arc::new(LargeStringArray::from(vec![agg::min_string(a)])),
                Arc::new(LargeStringArray::from(vec![agg::max_string(a)])),
            ))
        }
        DataType::Decimal128(precision, scale) => {
            let a = col.as_any().downcast_ref::<Decimal128Array>()?;
            Some((
                Arc::new(
                    Decimal128Array::from(vec![agg::min(a)])
                        .with_precision_and_scale(*precision, *scale)
                        .ok()?,
                ),
                Arc::new(
                    Decimal128Array::from(vec![agg::max(a)])
                        .with_precision_and_scale(*precision, *scale)
                        .ok()?,
                ),
            ))
        }

        // Temporal columns are numeric-backed and orderable, so min/max fold
        // (DataFusion's aggregate fast-path) and prune the same as integers.
        DataType::Date32 => prim!(Date32Array),
        DataType::Date64 => prim!(Date64Array),
        DataType::Time32(TimeUnit::Second) => prim!(Time32SecondArray),
        DataType::Time32(TimeUnit::Millisecond) => prim!(Time32MillisecondArray),
        DataType::Time64(TimeUnit::Microsecond) => prim!(Time64MicrosecondArray),
        DataType::Time64(TimeUnit::Nanosecond) => prim!(Time64NanosecondArray),
        DataType::Timestamp(TimeUnit::Second, tz) => ts!(TimestampSecondArray, tz),
        DataType::Timestamp(TimeUnit::Millisecond, tz) => ts!(TimestampMillisecondArray, tz),
        DataType::Timestamp(TimeUnit::Microsecond, tz) => ts!(TimestampMicrosecondArray, tz),
        DataType::Timestamp(TimeUnit::Nanosecond, tz) => ts!(TimestampNanosecondArray, tz),
        _ => None,
    }
}

/// Per-vector-column summary: the summary centroid plus the per-cluster
/// IVF centroids. Already produced by the superfile vector builder
/// (per-column, inside the vector blob's outer header KV metadata); the
/// writer copies them into the manifest at commit time. The per-cluster
/// centroids drive global cluster selection at query time.
#[derive(Debug, Clone)]
pub struct VectorSummary {
    /// Cluster centroid; length matches the vector column's `dim`
    /// declared in `SupertableOptions::vector_columns`.
    pub centroid: Vec<f32>,
    /// Fine IVF centroids grouped by their owning global cell. Packed-file
    /// flat cluster ordinals are derived from prefix sums over this list.
    pub cells: Vec<CellVectorSummary>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct CellVectorSummary {
    /// `Some(cell)` for MultiCell files; `None` for an unscoped legacy IVF.
    pub cell_id: Option<u32>,
    pub clusters: ClusterCentroids,
}

/// Bits per `u64` word in a packed centroid sign code.
pub(crate) const ADMIT_CODE_WORD_BITS: usize = 64;

/// Fraction of ranked cells the 1-bit admit prefilter keeps for exact
/// fp32 rescoring — shared by the query-side cell window and the
/// write-side assignment shortlist. 20% keeps the same coverage class as
/// the recall-validated 48-of-256 query window while scaling with the
/// population.
pub(crate) const RABITQ_ADMIT_CELL_SHORTLIST_FRACTION: f64 = 0.20;

/// Minimum meaningful prefilter window, from the recall-validated
/// 48-of-256 measurement: when the 20% slice comes out narrower than
/// this, the population is small enough that the exact scan is cheap and
/// the 1-bit estimate has nothing to buy — the query window floors here
/// (scoring everything below ~240 cells) and the write-side assignment
/// shortlist disengages entirely (exact scan).
pub(crate) const RABITQ_ADMIT_CELL_SHORTLIST_MIN: usize = 48;

/// Shared per-column state for the 1-bit admit prefilter: the column's
/// rotation, sign quantizer, and the Hamming→cosine lookup table
/// (`cos(π·h/dim)` — the standard sign-sketch angle estimator). Built
/// **once per query or per assignment batch** and shared across every
/// encoded vector — building rotation state per vector re-derives the
/// rotation thousands of times (measured ~51 ms of admit at 1M pre-drain
/// vs ~1 ms with shared state; the same waste per row on the write side).
#[derive(Debug, Clone)]
pub(crate) struct RabitqAdmitContext {
    rot_seed: u64,
    dim: usize,
    rotation: Arc<RandomRotation>,
    quant: BitQuantizer,
    /// `cos(π·h/dim)` for h in `0..=dim`.
    cos_table: Arc<Vec<f32>>,
}

impl RabitqAdmitContext {
    pub(crate) fn new(dim: usize, rot_seed: u64) -> Self {
        Self {
            rot_seed,
            dim,
            rotation: Arc::new(RandomRotation::new(dim, rot_seed)),
            quant: BitQuantizer::new(dim),
            cos_table: Arc::new(
                (0..=dim)
                    .map(|h| (PI * h as f32 / dim as f32).cos())
                    .collect(),
            ),
        }
    }

    /// Encode one vector against this context: rotate, sign-pack, and
    /// carry the norms the metric transforms need. Cheap per call (the
    /// rotation and cosine table are shared by `Arc`).
    pub(crate) fn encode(&self, vector: &[f32]) -> RabitqAdmitQuery {
        debug_assert_eq!(vector.len(), self.dim);
        let mut rotated = vec![0.0f32; self.dim];
        self.rotation.apply(vector, &mut rotated);
        let mut code = vec![0u8; self.quant.code_bytes()];
        self.quant.encode_rotated_into(&rotated, &mut code);
        let q_l2sq = dot(vector, vector);
        RabitqAdmitQuery {
            rot_seed: self.rot_seed,
            rotation: Arc::clone(&self.rotation),
            quant: self.quant.clone(),
            q_words: pack_code_bytes_to_words(&code),
            q_norm: q_l2sq.sqrt(),
            q_l2sq,
            cos_table: Arc::clone(&self.cos_table),
        }
    }
}

/// One encoded vector's 1-bit admit state: the packed sign code plus the
/// shared column context (rotation / quantizer / cosine table by `Arc`).
#[derive(Debug)]
pub(crate) struct RabitqAdmitQuery {
    rot_seed: u64,
    rotation: Arc<RandomRotation>,
    quant: BitQuantizer,
    /// Sign code packed into u64 words (zero-padded past `dim`).
    q_words: Vec<u64>,
    /// `‖q‖` and `‖q‖²` for the metric transforms.
    q_norm: f32,
    q_l2sq: f32,
    /// `cos(π·h/dim)` for h in `0..=dim`.
    cos_table: Arc<Vec<f32>>,
}

impl RabitqAdmitQuery {
    pub(crate) fn new(dim: usize, rot_seed: u64, query: &[f32]) -> Self {
        RabitqAdmitContext::new(dim, rot_seed).encode(query)
    }
}

/// One shared rotation + sign quantizer per vector column, for
/// hydration-time slab work over every summary instance.
fn admit_encoders(
    vector_columns: &[VectorConfig],
) -> HashMap<&str, (RandomRotation, BitQuantizer, u64)> {
    vector_columns
        .iter()
        .map(|vc| {
            (
                vc.column.as_str(),
                (
                    RandomRotation::new(vc.dim, vc.rot_seed),
                    BitQuantizer::new(vc.dim),
                    vc.rot_seed,
                ),
            )
        })
        .collect()
}

/// Read-only-consumer memory mode: for every uniquely-owned entry, build
/// each summary cell's 1-bit admit slab from its resident fp32 centroids
/// and then drop the fp32 vectors. One rotation + quantizer pair per
/// column, shared across all entries. Entries whose `Arc` is shared (a
/// previous snapshot or a loaded manifest part also references them) are
/// skipped — they were either stripped by the earlier load or belong to
/// maintenance state that needs fp32.
fn strip_summary_centroids(
    superfiles: &mut [Arc<SuperfileEntry>],
    vector_columns: &[VectorConfig],
) {
    let encoders = admit_encoders(vector_columns);
    if encoders.is_empty() {
        return;
    }
    for entry in superfiles.iter_mut() {
        let Some(entry) = Arc::get_mut(entry) else {
            continue;
        };
        for (column, summary) in entry.vector_summary.iter_mut() {
            let Some((rotation, quant, rot_seed)) = encoders.get(column.as_str()) else {
                continue;
            };
            for cell in &mut summary.cells {
                if cell.clusters.dim as usize != quant.dim {
                    continue;
                }
                cell.clusters
                    .strip_centroids_after_slab(rotation, quant, *rot_seed);
            }
        }
    }
}

/// Pre-build every summary cell's 1-bit admit slab at hydration, in
/// parallel on the table's reader pool. The slab is otherwise built
/// lazily on first scan, which lands the whole encode on the first
/// (cold) query — measured +1.4 s on a 100M-doc cold search (~105K fine
/// centroids, one rotation+sign-pack each, single-threaded). Open
/// absorbs the same work in a rayon pass instead. Idempotent: stripped
/// or already-warm instances are `OnceLock` no-ops.
fn prewarm_summary_admit_slabs(
    superfiles: &[Arc<SuperfileEntry>],
    vector_columns: &[VectorConfig],
    pool: &ThreadPool,
) {
    let encoders = admit_encoders(vector_columns);
    if encoders.is_empty() {
        return;
    }
    pool.install(|| {
        superfiles.par_iter().for_each(|entry| {
            for (column, summary) in &entry.vector_summary {
                let Some((rotation, quant, rot_seed)) = encoders.get(column.as_str()) else {
                    continue;
                };
                for cell in &summary.cells {
                    if cell.clusters.dim as usize != quant.dim || !cell.clusters.vectors_resident()
                    {
                        continue;
                    }
                    cell.clusters
                        .prewarm_admit_codes(rotation, quant, *rot_seed);
                }
            }
        });
    });
}

/// Pack a byte sign code into little-endian u64 words, zero-padding the
/// tail. Zero pad bits match on both sides of an XOR, so they never
/// contribute to the Hamming distance.
fn pack_code_bytes_to_words(code: &[u8]) -> Vec<u64> {
    let bytes_per_word = ADMIT_CODE_WORD_BITS / 8;
    code.chunks(bytes_per_word)
        .map(|chunk| {
            let mut word = [0u8; 8];
            word[..chunk.len()].copy_from_slice(chunk);
            u64::from_le_bytes(word)
        })
        .collect()
}

/// XOR + popcount Hamming distance over packed sign codes. Safe Rust —
/// `count_ones` lowers to the POPCNT instruction on x86-64.
#[inline]
fn hamming_words(a: &[u64], b: &[u64]) -> u32 {
    debug_assert_eq!(a.len(), b.len());
    a.iter().zip(b).map(|(x, y)| (x ^ y).count_ones()).sum()
}

/// Packed 1-bit sign codes for every centroid in a [`ClusterCentroids`],
/// plus per-centroid norms for the metric transforms. Computed wherever
/// the centroids are computed (commit staging, drain packs) and persisted
/// beside the fp32 in the summary wire blob, so hydration decodes the
/// slab instead of re-deriving one rotation per fine centroid; legacy
/// fp32-only blobs still derive it at hydration.
#[derive(Debug, Clone, PartialEq)]
pub(crate) struct RabitqAdmitCodes {
    pub(crate) rot_seed: u64,
    pub(crate) words_per_code: usize,
    /// `n_cent * words_per_code`, cluster-major.
    pub(crate) codes: Vec<u64>,
    /// `‖centroid[c]‖` per cluster.
    pub(crate) norms: Vec<f32>,
}

/// Per-cluster IVF centroids for one vector column, stored canonically as fp32
/// cluster-major (`n_cent * dim`) plus a derived block-transposed cache for hot
/// routing. Carried in the manifest so a query can rank every superfile's
/// clusters globally — without opening the superfile — and probe only the
/// globally-closest clusters. The 1-bit shortlist + rerank still run on the
/// superfile's on-disk compressed vectors; these drive cluster *selection* only.
///
/// Centroids are `n_cent * dim` (~1% of index bytes), so they are kept
/// fp32, no per-query dequant. (Rerank rows, the bulk of the index, stay
/// Sq8+ε; representation follows cardinality.) Every scan-shaped read —
/// [`Self::score_clusters_into`], [`Self::rank_cells`],
/// [`Self::nearest_cell`], boundary assignment — goes through the blocked
/// SIMD kernels in `superfile::vector::distance` over [`Self::transposed`],
/// the lazily-built block-transposed cache. [`Self::score_one`] stays a
/// zero-copy single-centroid [`distance`] probe.
///
/// The 1-bit admit prefilter ([`Self::estimate_min_admit_score`]) ranks
/// whole instances cheaply from packed sign codes; exact fp32 scoring then
/// runs only on the shortlisted cells, so final routing scores are always
/// exact.
#[derive(Debug, Default)]
pub struct ClusterCentroids {
    pub n_cent: u32,
    pub dim: u32,
    /// Per-cluster centroid, fp32, cluster-major (`n_cent * dim`).
    pub centroids: Vec<f32>,
    /// Per-cluster indexed doc count; length `n_cent`. Count-0 clusters
    /// are skipped by the selector.
    pub counts: Vec<u32>,
    /// Lazily-built block-transposed centroid cache feeding the blocked
    /// SIMD scan kernels in `superfile::vector::distance`. Built once per
    /// instance on first scan; reset by `Clone` (a clone may mutate
    /// `centroids`, so it re-derives its own cache on first use).
    transposed: OnceLock<Vec<f32>>,
    /// Lazily-built packed sign codes for the 1-bit admit prefilter.
    admit_codes: OnceLock<RabitqAdmitCodes>,
}

impl Clone for ClusterCentroids {
    fn clone(&self) -> Self {
        // Preserve warm scan caches when present. Dropping the transposed
        // cache on every clone forced the query path (which historically
        // cloned the global grid / VectorCell strategy each search) to
        // rebuild the scalar block-transpose — milliseconds at dim=1024 —
        // before the SIMD scan could run. Callers that mutate `centroids`
        // after cloning must [`Self::invalidate_transposed`].
        let transposed = OnceLock::new();
        if let Some(cache) = self.transposed.get() {
            let _ = transposed.set(cache.clone());
        }
        let admit_codes = OnceLock::new();
        if let Some(cache) = self.admit_codes.get() {
            let _ = admit_codes.set(cache.clone());
        }
        Self {
            n_cent: self.n_cent,
            dim: self.dim,
            centroids: self.centroids.clone(),
            counts: self.counts.clone(),
            transposed,
            admit_codes,
        }
    }
}

impl PartialEq for ClusterCentroids {
    fn eq(&self, other: &Self) -> bool {
        self.n_cent == other.n_cent
            && self.dim == other.dim
            && self.centroids == other.centroids
            && self.counts == other.counts
    }
}

impl Eq for ClusterCentroids {}

impl ClusterCentroids {
    /// The "no cluster centroids" value — a superfile without a vector
    /// index for the column.
    pub fn empty() -> Self {
        Self::default()
    }

    pub fn is_empty(&self) -> bool {
        self.n_cent == 0
    }

    /// Zero-copy fp32 slice of cluster `c`'s centroid (length `dim`).
    pub fn centroid(&self, c: usize) -> &[f32] {
        // Same residency guard as `transposed()` / `build_admit_codes()`:
        // on a stripped summary this would otherwise fail as an
        // out-of-bounds slice, hiding the actual invariant breach.
        assert!(
            self.vectors_resident(),
            "centroid() on a stripped summary — fp32 centroids are not resident"
        );
        let d = self.dim as usize;
        let base = c * d;
        &self.centroids[base..base + d]
    }

    /// Cluster-major fp32 centroids (`n_cent * dim`) — a clone of the
    /// stored buffer.
    pub fn to_fp32(&self) -> Vec<f32> {
        self.centroids.clone()
    }

    /// Store fp32 cluster centroids (`centroids` is cluster-major,
    /// `n_cent * dim` floats) directly. Non-finite components are clamped
    /// to zero so routing distance stays well-defined.
    pub fn from_fp32(n_cent: u32, dim: u32, centroids: &[f32], counts: Vec<u32>) -> Self {
        let stored: Vec<f32> = centroids
            .iter()
            .map(|v| if v.is_finite() { *v } else { 0.0 })
            .collect();
        Self::from_decoded(n_cent, dim, stored, counts)
    }

    /// Wrap already-validated fp32 centroids (wire decode path — bytes were
    /// written by [`Self::from_fp32`], so the clamp already happened).
    pub(crate) fn from_decoded(
        n_cent: u32,
        dim: u32,
        centroids: Vec<f32>,
        counts: Vec<u32>,
    ) -> Self {
        // A grid must carry exactly one count and one centroid per cell. A
        // mismatch (e.g. counts left at the old length after a split) silently
        // passes in memory but truncates the wire encoding — counts and centroids
        // are serialized adjacently — so the grid fails to reopen from storage.
        // Assert here to catch the malformed construction at its source.
        debug_assert_eq!(
            counts.len(),
            n_cent as usize,
            "cluster grid counts ({}) must match n_cent ({n_cent})",
            counts.len()
        );
        debug_assert_eq!(
            centroids.len(),
            n_cent as usize * dim as usize,
            "cluster grid centroids ({}) must be n_cent*dim ({}*{})",
            centroids.len(),
            n_cent,
            dim
        );
        Self {
            n_cent,
            dim,
            centroids,
            counts,
            transposed: OnceLock::new(),
            admit_codes: OnceLock::new(),
        }
    }

    /// The block-transposed centroid cache feeding the blocked SIMD scan
    /// kernels — built once per instance on first scan, shared by every
    /// scan-shaped method below and by boundary assignment. This is the ONLY
    /// sanctioned way to scan these centroids; do not hand-roll
    /// `(0..n_cent).map(distance)` loops against [`Self::centroid`].
    pub(crate) fn transposed(&self) -> &[f32] {
        assert!(
            self.vectors_resident(),
            "fp32 centroids were dropped (summary_centroids_from_superfiles); \
             exact scans must read the superfile centroid regions"
        );
        self.transposed.get_or_init(|| {
            transpose_centroids_cluster_major(
                &self.centroids,
                self.n_cent as usize,
                self.dim as usize,
            )
        })
    }

    /// Drop the transposed / admit-code scan caches after mutating
    /// [`Self::centroids`] (or `counts` / `n_cent` / `dim`) on a value that
    /// may already have been scanned. The next scan rebuilds them.
    ///
    /// Not called on the read path today (centroids are immutable after
    /// decode); kept for write/maintenance sites that mutate in place.
    #[allow(dead_code)]
    pub(crate) fn invalidate_transposed(&mut self) {
        self.transposed = OnceLock::new();
        self.admit_codes = OnceLock::new();
    }

    /// Whether the fp32 centroid vectors are resident. `false` only after
    /// [`Self::strip_centroids_after_slab`] (read-only consumer memory
    /// mode) — exact scans must then read the superfile centroid regions
    /// instead of this struct.
    pub(crate) fn vectors_resident(&self) -> bool {
        self.n_cent == 0 || !self.centroids.is_empty()
    }

    /// Build the packed 1-bit admit codes + norms from the resident fp32
    /// centroids. Shared by the lazy per-query cache fill and the eager
    /// hydration-time build that precedes a centroid strip.
    fn build_admit_codes(
        &self,
        rotation: &RandomRotation,
        quant: &BitQuantizer,
        rot_seed: u64,
    ) -> RabitqAdmitCodes {
        assert!(
            self.vectors_resident(),
            "admit codes need resident fp32 centroids; this summary was stripped"
        );
        let dim = self.dim as usize;
        let n_cent = self.n_cent as usize;
        let words_per_code = dim.div_ceil(ADMIT_CODE_WORD_BITS);
        let mut codes = vec![0u64; n_cent.saturating_mul(words_per_code)];
        let mut norms = vec![0.0f32; n_cent];
        let mut rotated = vec![0.0f32; dim];
        let mut byte_code = vec![0u8; quant.code_bytes()];
        for c in 0..n_cent {
            let centroid = self.centroid(c);
            norms[c] = dot(centroid, centroid).sqrt();
            rotation.apply(centroid, &mut rotated);
            quant.encode_rotated_into(&rotated, &mut byte_code);
            codes[c * words_per_code..(c + 1) * words_per_code]
                .copy_from_slice(&pack_code_bytes_to_words(&byte_code));
        }
        RabitqAdmitCodes {
            rot_seed,
            words_per_code,
            codes,
            norms,
        }
    }

    /// Read-only-consumer memory mode: eagerly build the 1-bit admit slab,
    /// then drop the fp32 centroid vectors (and the transposed cache) from
    /// memory. `counts`, `n_cent`, and `dim` stay resident — the flat
    /// cluster id math and posting budgets depend on them. Idempotent.
    pub(crate) fn strip_centroids_after_slab(
        &mut self,
        rotation: &RandomRotation,
        quant: &BitQuantizer,
        rot_seed: u64,
    ) {
        if self.n_cent == 0 || self.centroids.is_empty() {
            return;
        }
        let codes = self.build_admit_codes(rotation, quant, rot_seed);
        self.admit_codes = OnceLock::new();
        let _ = self.admit_codes.set(codes);
        self.centroids = Vec::new();
        self.transposed = OnceLock::new();
    }

    /// Packed sign codes for the 1-bit admit prefilter — built once per
    /// instance from the resident fp32 centroids with the query's shared
    /// rotation/quantizer (no per-instance rotation state). Pre-populated
    /// at hydration ([`prewarm_summary_admit_slabs`]) and by
    /// [`Self::strip_centroids_after_slab`] on stripped summaries.
    fn admit_codes(&self, admit: &RabitqAdmitQuery) -> &RabitqAdmitCodes {
        let cache = self.admit_codes.get_or_init(|| {
            self.build_admit_codes(admit.rotation.as_ref(), &admit.quant, admit.rot_seed)
        });
        // Release assert, mirroring the superfile reader's hard error on a
        // rot_seed mismatch: scoring a slab built under a different
        // rotation silently corrupts admit ranking (a recall bug with no
        // crash), which is strictly worse than failing loudly here.
        assert_eq!(
            cache.rot_seed, admit.rot_seed,
            "admit codes built with a different rot_seed"
        );
        cache
    }

    /// Hydration-time slab fill: build the packed admit codes now so the
    /// first query does not pay the encode. `OnceLock` no-op when already
    /// built (a reload reusing warm entries, or a stripped summary).
    pub(crate) fn prewarm_admit_codes(
        &self,
        rotation: &RandomRotation,
        quant: &BitQuantizer,
        rot_seed: u64,
    ) {
        let _ = self
            .admit_codes
            .get_or_init(|| self.build_admit_codes(rotation, quant, rot_seed));
    }

    /// The built admit slab, if any — the summary wire encoder persists it
    /// beside the fp32 centroids when present.
    pub(crate) fn admit_codes_built(&self) -> Option<&RabitqAdmitCodes> {
        self.admit_codes.get()
    }

    /// Wire-decode constructor for routing-only summary blocks (`CFR0`):
    /// no fp32 payload on the wire, so the instance lands directly in the
    /// stripped shape ([`Self::vectors_resident`] = false) with the admit
    /// slab seeded — the same state [`Self::strip_centroids_after_slab`]
    /// produces from a full instance.
    pub(crate) fn from_decoded_routing(
        n_cent: u32,
        dim: u32,
        counts: Vec<u32>,
        admit: RabitqAdmitCodes,
    ) -> Self {
        debug_assert_eq!(
            counts.len(),
            n_cent as usize,
            "routing cluster counts ({}) must match n_cent ({n_cent})",
            counts.len()
        );
        Self {
            n_cent,
            dim,
            centroids: Vec::new(),
            counts,
            transposed: OnceLock::new(),
            admit_codes: {
                let lock = OnceLock::new();
                let _ = lock.set(admit);
                lock
            },
        }
    }

    /// 1-bit prefilter: the best (smallest) estimated admit score across
    /// this instance's populated clusters, from XOR+popcount over packed
    /// sign codes. `None` when no cluster is populated. Estimates rank
    /// cells for the exact-rescore shortlist only — they never feed
    /// routing or near-tie logic directly.
    pub(crate) fn estimate_min_admit_score(
        &self,
        metric: Metric,
        admit: &RabitqAdmitQuery,
    ) -> Option<f32> {
        let mut best: Option<f32> = None;
        self.estimate_admit_scores_into(metric, admit, |_, score| {
            best = Some(best.map_or(score, |b: f32| b.min(score)));
        });
        best
    }

    /// 1-bit prefilter shortlist over this instance's clusters: rank every
    /// populated cluster by its estimated admit score (same XOR+popcount
    /// estimator as [`Self::estimate_min_admit_score`]) and return the top
    /// `window` cluster ids, ascending by estimate. The write-side
    /// assignment prefilter: exact fp32 scoring then runs only on the
    /// returned ids, so the final placement is exact within the window.
    pub(crate) fn admit_shortlist(
        &self,
        metric: Metric,
        admit: &RabitqAdmitQuery,
        window: usize,
    ) -> Vec<(u32, f32)> {
        let mut top: Vec<(u32, f32)> = Vec::with_capacity(window.saturating_add(1));
        self.estimate_admit_scores_into(metric, admit, |c, score| {
            insert_ranked(&mut top, window, c, score);
        });
        top
    }

    /// Emit every populated cluster's estimated admit score — the shared
    /// XOR+popcount estimator behind [`Self::estimate_min_admit_score`],
    /// [`Self::admit_shortlist`], and the user-path stripped-summary fine
    /// scoring (which ranks fragments on the resident 1-bit slab instead
    /// of fetching fp32 per (file, cell)).
    pub(crate) fn estimate_admit_scores_into(
        &self,
        metric: Metric,
        admit: &RabitqAdmitQuery,
        mut emit: impl FnMut(u32, f32),
    ) {
        debug_assert_eq!(admit.cos_table.len(), self.dim as usize + 1);
        let cache = self.admit_codes(admit);
        let w = cache.words_per_code;
        for c in 0..self.n_cent as usize {
            if self.counts[c] == 0 {
                continue;
            }
            let code = &cache.codes[c * w..(c + 1) * w];
            let h = hamming_words(&admit.q_words, code) as usize;
            let est_dot = admit.cos_table[h] * admit.q_norm * cache.norms[c];
            let score = match metric {
                Metric::Cosine => COSINE_DISTANCE_BASE - est_dot,
                Metric::NegDot => -est_dot,
                Metric::L2Sq => {
                    let c_norm = cache.norms[c];
                    admit.q_l2sq + c_norm * c_norm - L2_CROSS_TERM_COEFF * est_dot
                }
            };
            emit(c as u32, score);
        }
    }

    /// Score cluster `c` against `query`: [`distance`] on the fp32 centroid
    /// slice (zero-copy, no dequant). Single-centroid probe — for scans use
    /// [`Self::score_clusters_into`] / [`Self::rank_cells`].
    pub fn score_one(&self, metric: Metric, c: usize, query: &[f32]) -> f32 {
        debug_assert_eq!(query.len(), self.dim as usize);
        distance(metric, query, self.centroid(c))
    }

    /// Score every populated cluster via the blocked SIMD kernel over the
    /// cached transposed layout. Calls `emit(cluster_id, score)` in ascending
    /// cluster order for each cluster with a nonzero indexed count.
    pub fn score_clusters_into(
        &self,
        metric: Metric,
        query: &[f32],
        mut emit: impl FnMut(u32, f32),
    ) {
        debug_assert_eq!(query.len(), self.dim as usize);
        let n_cent = self.n_cent as usize;
        let scores = all_centroid_scores_transposed(
            metric,
            query,
            self.transposed(),
            n_cent,
            self.dim as usize,
        );
        for (c, &score) in scores.iter().enumerate() {
            if self.counts[c] == 0 {
                continue;
            }
            emit(c as u32, score);
        }
    }

    /// Rank every cell (including count-0 cells) against `query`: ascending
    /// score, ties broken by lower cell id. The full-ranking shape the cell
    /// routing cutoff consumes; scored by the blocked SIMD kernel.
    pub fn rank_cells(&self, metric: Metric, query: &[f32]) -> Vec<(u32, f32)> {
        debug_assert_eq!(query.len(), self.dim as usize);
        let n_cent = self.n_cent as usize;
        let scores = all_centroid_scores_transposed(
            metric,
            query,
            self.transposed(),
            n_cent,
            self.dim as usize,
        );
        let mut ranked: Vec<(u32, f32)> = scores
            .into_iter()
            .enumerate()
            .map(|(c, score)| (c as u32, score))
            .collect();
        ranked.sort_unstable_by(|a, b| {
            a.1.partial_cmp(&b.1)
                .unwrap_or(Ordering::Equal)
                .then_with(|| a.0.cmp(&b.0))
        });
        ranked
    }

    /// Return the cell whose centroid is closest to `query` under `metric`
    /// (count-0 cells excluded; 0 when every cell is empty). Blocked SIMD
    /// top-1 over the cached transposed layout.
    pub fn nearest_cell(&self, metric: Metric, query: &[f32]) -> u32 {
        debug_assert_eq!(query.len(), self.dim as usize);
        nearest_k_centroids_transposed(
            metric,
            query,
            self.transposed(),
            self.n_cent as usize,
            self.dim as usize,
            Some(&self.counts),
            1,
        )
        .first()
        .map(|&(cell, _)| cell)
        .unwrap_or(0)
    }

    /// Assign each row in `vectors` to its nearest cell. Parallel over rows;
    /// each assignment uses [`Self::nearest_cell`].
    pub fn assign_rows(&self, metric: Metric, vectors: &[f32], assignments: &mut [u32]) {
        let dim = self.dim as usize;
        assert_eq!(vectors.len() % dim, 0, "assign_rows: vectors len mismatch");
        let n = vectors.len() / dim;
        assert_eq!(
            assignments.len(),
            n,
            "assign_rows: assignments len mismatch"
        );
        if n == 0 {
            return;
        }
        assignments
            .par_iter_mut()
            .enumerate()
            .for_each(|(d, slot)| {
                *slot = self.nearest_cell(metric, &vectors[d * dim..(d + 1) * dim]);
            });
    }
}

#[cfg(test)]
mod tests {
    use std::{hint::black_box, slice::from_ref, sync::Arc, time::Instant};

    use arrow_array::{
        Array, Date32Array, Date64Array, Int64Array, Time64MicrosecondArray,
        TimestampMicrosecondArray,
    };
    use arrow_schema::{DataType, Field, Schema, TimeUnit};
    use dashmap::DashMap;
    use datafusion::scalar::ScalarValue;
    use tempfile::TempDir;
    use tokio::sync::OnceCell;

    use super::*;
    use crate::{
        storage::LocalFsStorageProvider,
        superfile::{builder::FtsConfig, vector::distance::distance},
        supertable::manifest::{
            commit::{PartWriteResult, write_manifest_part},
            list::{Manifest, PartitionStrategy},
        },
        test_helpers::default_tokenizer,
    };

    /// Deterministic synthetic fp32 centroids for cluster-scoring tests.
    fn synth_clusters(n_cent: u32, dim: u32, seed: u64) -> (ClusterCentroids, Vec<f32>) {
        let (nc, d) = (n_cent as usize, dim as usize);
        let mut centroids = vec![0f32; nc * d];
        for c in 0..nc {
            for j in 0..d {
                let v = ((seed + (c * d + j) as u64 * 2_654_435_761) % 1000) as f32 / 250.0 - 2.0
                    + c as f32 * 0.1;
                centroids[c * d + j] = v;
            }
        }
        let counts: Vec<u32> = (0..nc).map(|c| if c == nc / 2 { 0 } else { 10 }).collect();
        let cc = ClusterCentroids::from_fp32(n_cent, dim, &centroids, counts);
        (cc, centroids)
    }

    #[test]
    fn min_max_stats_record_and_fold_all_null_columns() {
        let arr = |vals: Vec<Option<i64>>| Arc::new(Int64Array::from(vals)) as ArrayRef;
        let scalar = |a: &ArrayRef| ScalarValue::try_from_array(a, 0).expect("decode");

        // All-null column still yields a stat, with null min/max (so the
        // null count is recorded and `IS [NOT] NULL` can prune on it).
        let (mn, mx) = column_min_max(&arr(vec![None, None])).expect("all-null stat");
        assert!(mn.is_null(0) && mx.is_null(0));

        // Populated column → real min/max, nulls ignored.
        let (mn, mx) = column_min_max(&arr(vec![Some(5), Some(2), None])).expect("stat");
        assert_eq!(scalar(&mn), ScalarValue::Int64(Some(2)));
        assert_eq!(scalar(&mx), ScalarValue::Int64(Some(5)));

        // Fold: a real bound wins over a null bound; both-null stays null.
        let null1 = arr(vec![None]);
        let (mn, mx) =
            merge_min_max_arrays(&null1, &arr(vec![Some(2)]), &null1, &arr(vec![Some(9)]))
                .expect("merge real over null");
        assert_eq!(scalar(&mn), ScalarValue::Int64(Some(2)));
        assert_eq!(scalar(&mx), ScalarValue::Int64(Some(9)));
        let (mn, mx) = merge_min_max_arrays(&null1, &null1, &null1, &null1).expect("merge null");
        assert!(mn.is_null(0) && mx.is_null(0));
    }

    #[test]
    fn min_max_stats_cover_temporal_columns() {
        let scalar = |a: &ArrayRef| ScalarValue::try_from_array(a, 0).expect("decode");

        // Date32 (the ClickBench `EventDate` case that used to carry no stat):
        // numeric-backed, so min/max record and fold like an integer.
        let d: ArrayRef = Arc::new(Date32Array::from(vec![Some(20100), Some(19000), None]));
        let (mn, mx) = column_min_max(&d).expect("date stat");
        assert_eq!(scalar(&mn), ScalarValue::Date32(Some(19000)));
        assert_eq!(scalar(&mx), ScalarValue::Date32(Some(20100)));

        // Two superfiles' date bounds fold to the outer extremes.
        let lo: ArrayRef = Arc::new(Date32Array::from(vec![Some(19000)]));
        let hi: ArrayRef = Arc::new(Date32Array::from(vec![Some(20100)]));
        let olo: ArrayRef = Arc::new(Date32Array::from(vec![Some(18000)]));
        let ohi: ArrayRef = Arc::new(Date32Array::from(vec![Some(21000)]));
        let (mn, mx) = merge_min_max_arrays(&lo, &olo, &hi, &ohi).expect("date merge");
        assert_eq!(scalar(&mn), ScalarValue::Date32(Some(18000)));
        assert_eq!(scalar(&mx), ScalarValue::Date32(Some(21000)));

        // Timestamp keeps its timezone through both build and merge. A
        // naive-vs-zoned mismatch would fail the merge and silently drop the
        // stat, so assert the type survives, not just the value.
        let tz = "+05:30";
        let ts: ArrayRef = Arc::new(
            TimestampMicrosecondArray::from(vec![Some(200i64), Some(100)]).with_timezone(tz),
        );
        let zoned = DataType::Timestamp(TimeUnit::Microsecond, Some(tz.into()));
        let (mn, mx) = column_min_max(&ts).expect("ts stat");
        assert_eq!(mn.data_type(), &zoned);
        assert_eq!(
            scalar(&mn),
            ScalarValue::TimestampMicrosecond(Some(100), Some(tz.into()))
        );
        assert_eq!(
            scalar(&mx),
            ScalarValue::TimestampMicrosecond(Some(200), Some(tz.into()))
        );
        let (mmn, _mmx) = merge_min_max_arrays(&mn, &mn, &mx, &mx).expect("ts merge keeps tz");
        assert_eq!(mmn.data_type(), &zoned);

        // Date64 (ms-since-epoch) and Time64 ride the same `prim!` arm as
        // Date32; spot-check that each records and reconstructs to its type.
        let d64: ArrayRef = Arc::new(Date64Array::from(vec![Some(9i64), Some(2)]));
        assert_eq!(
            scalar(&column_min_max(&d64).expect("date64 stat").0),
            ScalarValue::Date64(Some(2))
        );
        let t64: ArrayRef = Arc::new(Time64MicrosecondArray::from(vec![Some(7i64), Some(3)]));
        assert_eq!(
            scalar(&column_min_max(&t64).expect("time64 stat").0),
            ScalarValue::Time64Microsecond(Some(3))
        );
    }

    /// Every supported column type must fold through `merge_min_max_arrays`
    /// keeping the smaller `min` and the larger `max`, and the merged bound
    /// must reconstruct to the column's own scalar type. A missing arm (or a
    /// type drift on reconstruction) fails the downcast and silently drops the
    /// stat, regressing the range prune for that type — so assert both the
    /// value fold and the reconstructed `ScalarValue` for each.
    #[test]
    fn merge_min_max_folds_every_supported_column_type() {
        let scalar = |a: &ArrayRef| ScalarValue::try_from_array(a, 0).expect("decode");
        // min-pair = (hi, lo) ⇒ lo survives; max-pair = (lo, hi) ⇒ hi survives.
        let fold =
            |lo: ArrayRef, hi: ArrayRef| merge_min_max_arrays(&hi, &lo, &lo, &hi).expect("merge");

        macro_rules! prim_case {
            ($arr:ty, $sv:path, $lo:expr, $hi:expr) => {{
                let lo: ArrayRef = Arc::new(<$arr>::from(vec![Some($lo)]));
                let hi: ArrayRef = Arc::new(<$arr>::from(vec![Some($hi)]));
                let (mn, mx) = fold(lo, hi);
                assert_eq!(
                    scalar(&mn),
                    $sv(Some($lo)),
                    concat!(stringify!($arr), " min")
                );
                assert_eq!(
                    scalar(&mx),
                    $sv(Some($hi)),
                    concat!(stringify!($arr), " max")
                );
            }};
        }

        prim_case!(UInt8Array, ScalarValue::UInt8, 1u8, 9u8);
        prim_case!(UInt16Array, ScalarValue::UInt16, 1u16, 9u16);
        prim_case!(UInt32Array, ScalarValue::UInt32, 1u32, 9u32);
        prim_case!(UInt64Array, ScalarValue::UInt64, 1u64, 9u64);
        prim_case!(Int8Array, ScalarValue::Int8, -3i8, 4i8);
        prim_case!(Int16Array, ScalarValue::Int16, -3i16, 4i16);
        prim_case!(Int32Array, ScalarValue::Int32, -3i32, 4i32);
        prim_case!(Float32Array, ScalarValue::Float32, -1.5f32, 2.5f32);
        prim_case!(Float64Array, ScalarValue::Float64, -1.5f64, 2.5f64);
        prim_case!(Date64Array, ScalarValue::Date64, 2i64, 9i64);
        prim_case!(Time32SecondArray, ScalarValue::Time32Second, 2i32, 9i32);
        prim_case!(
            Time32MillisecondArray,
            ScalarValue::Time32Millisecond,
            2i32,
            9i32
        );
        prim_case!(
            Time64NanosecondArray,
            ScalarValue::Time64Nanosecond,
            2i64,
            9i64
        );

        // `false < true`: min folds like AND, max like OR.
        let (mn, mx) = fold(
            Arc::new(BooleanArray::from(vec![Some(false)])),
            Arc::new(BooleanArray::from(vec![Some(true)])),
        );
        assert_eq!(scalar(&mn), ScalarValue::Boolean(Some(false)), "bool min");
        assert_eq!(scalar(&mx), ScalarValue::Boolean(Some(true)), "bool max");

        // Utf8 / LargeUtf8 fold lexicographically.
        let (mn, mx) = fold(
            Arc::new(StringArray::from(vec![Some("apple")])),
            Arc::new(StringArray::from(vec![Some("pear")])),
        );
        assert_eq!(
            scalar(&mn),
            ScalarValue::Utf8(Some("apple".into())),
            "utf8 min"
        );
        assert_eq!(
            scalar(&mx),
            ScalarValue::Utf8(Some("pear".into())),
            "utf8 max"
        );
        let (mn, mx) = fold(
            Arc::new(LargeStringArray::from(vec![Some("apple")])),
            Arc::new(LargeStringArray::from(vec![Some("pear")])),
        );
        assert_eq!(
            scalar(&mn),
            ScalarValue::LargeUtf8(Some("apple".into())),
            "largeutf8 min"
        );
        assert_eq!(
            scalar(&mx),
            ScalarValue::LargeUtf8(Some("pear".into())),
            "largeutf8 max"
        );

        // Decimal128 keeps precision/scale through the fold.
        let dec = |v: i128| -> ArrayRef {
            Arc::new(
                Decimal128Array::from(vec![Some(v)])
                    .with_precision_and_scale(10, 2)
                    .expect("decimal"),
            )
        };
        let (mn, mx) = fold(dec(125), dec(999));
        assert_eq!(
            scalar(&mn),
            ScalarValue::Decimal128(Some(125), 10, 2),
            "dec min"
        );
        assert_eq!(
            scalar(&mx),
            ScalarValue::Decimal128(Some(999), 10, 2),
            "dec max"
        );

        // Timestamp arms other than the Microsecond one covered above; a
        // naive (tz-less) timestamp must fold and reconstruct with `None` tz.
        let (mn, mx) = fold(
            Arc::new(TimestampSecondArray::from(vec![Some(100i64)])),
            Arc::new(TimestampSecondArray::from(vec![Some(200i64)])),
        );
        assert_eq!(
            scalar(&mn),
            ScalarValue::TimestampSecond(Some(100), None),
            "ts-sec min"
        );
        assert_eq!(
            scalar(&mx),
            ScalarValue::TimestampSecond(Some(200), None),
            "ts-sec max"
        );
        let (mn, _mx) = fold(
            Arc::new(TimestampNanosecondArray::from(vec![Some(100i64)])),
            Arc::new(TimestampNanosecondArray::from(vec![Some(200i64)])),
        );
        assert_eq!(
            scalar(&mn),
            ScalarValue::TimestampNanosecond(Some(100), None),
            "ts-nano min"
        );
    }

    /// Cloning a warm [`ClusterCentroids`] must keep the transposed cache so a
    /// subsequent scan does not pay the scalar transpose rebuild.
    #[test]
    fn clone_preserves_warm_transposed_cache() {
        let (cc, _) = synth_clusters(32, 128, 3);
        let warm = cc.transposed().as_ptr();
        assert!(cc.transposed.get().is_some());
        let cloned = cc.clone();
        assert!(
            cloned.transposed.get().is_some(),
            "clone must carry a warm transposed cache"
        );
        // Same bytes, distinct allocation (Vec clone) — pointer differs, length matches.
        assert_eq!(cloned.transposed().len(), cc.transposed().len());
        assert_ne!(
            cloned.transposed().as_ptr(),
            warm,
            "clone owns its own cache buffer"
        );
        let mut mutated = cc.clone();
        mutated.centroids[0] += 1.0;
        mutated.invalidate_transposed();
        assert!(mutated.transposed.get().is_none());
        let _ = mutated.transposed(); // rebuild
        assert!(mutated.transposed.get().is_some());
    }

    /// The 1-bit admit estimate must prefer the instance holding the
    /// query's true nearest centroid on separated fixtures, for every
    /// metric — the property the exact-rescore cell shortlist rides on.
    #[test]
    fn admit_estimate_prefers_matching_centroid_instance() {
        const DIM: usize = 128;
        const ROT_SEED: u64 = 7;
        // Two single-centroid instances on different axes.
        let mut near = vec![0.0f32; DIM];
        near[0] = 1.0;
        let mut far = vec![0.0f32; DIM];
        far[5] = 1.0;
        let a = ClusterCentroids::from_fp32(1, DIM as u32, &near, vec![1]);
        let b = ClusterCentroids::from_fp32(1, DIM as u32, &far, vec![1]);
        // Query beside `near`, small off-axis noise.
        let mut query = near.clone();
        query[1] = 0.05;
        let admit = RabitqAdmitQuery::new(DIM, ROT_SEED, &query);
        for metric in [Metric::Cosine, Metric::L2Sq, Metric::NegDot] {
            let ea = a
                .estimate_min_admit_score(metric, &admit)
                .expect("a populated");
            let eb = b
                .estimate_min_admit_score(metric, &admit)
                .expect("b populated");
            assert!(
                ea < eb,
                "{metric:?}: matching instance must rank first ({ea} vs {eb})"
            );
        }
        // Count-0 clusters are skipped: an unpopulated instance has no
        // estimate to contribute.
        let unpopulated = ClusterCentroids::from_fp32(1, DIM as u32, &near, vec![0]);
        assert!(
            unpopulated
                .estimate_min_admit_score(Metric::Cosine, &admit)
                .is_none()
        );
        // Clone carries the warm admit-code slab.
        let cloned = a.clone();
        assert!(cloned.admit_codes.get().is_some());
    }

    /// Stripping keeps `counts`/`n_cent`/`dim` and the pre-built admit
    /// slab, drops the fp32 vectors, and stays idempotent; estimates keep
    /// serving from the slab afterward.
    #[test]
    fn strip_centroids_keeps_slab_and_counts() {
        const DIM: usize = 64;
        const ROT_SEED: u64 = 7;
        let mut flat = vec![0.0f32; 2 * DIM];
        flat[0] = 1.0;
        flat[DIM + 5] = 1.0;
        let mut cc = ClusterCentroids::from_fp32(2, DIM as u32, &flat, vec![3, 4]);
        let rotation = RandomRotation::new(DIM, ROT_SEED);
        let quant = BitQuantizer::new(DIM);
        cc.strip_centroids_after_slab(&rotation, &quant, ROT_SEED);
        assert!(!cc.vectors_resident());
        assert_eq!(cc.n_cent, 2);
        assert_eq!(cc.counts, vec![3, 4]);
        assert!(cc.centroids.is_empty());
        let mut query = vec![0.0f32; DIM];
        query[0] = 1.0;
        let admit = RabitqAdmitQuery::new(DIM, ROT_SEED, &query);
        assert!(
            cc.estimate_min_admit_score(Metric::Cosine, &admit)
                .is_some(),
            "estimates must keep serving from the pre-built slab"
        );
        // Idempotent (a reload may strip already-stripped clones).
        cc.strip_centroids_after_slab(&rotation, &quant, ROT_SEED);
        assert!(!cc.vectors_resident());
        // Clone carries the stripped state + slab.
        let cloned = cc.clone();
        assert!(!cloned.vectors_resident());
        assert!(cloned.admit_codes.get().is_some());
    }

    /// Exact scans on a stripped summary must fail loudly — the caller is
    /// required to route through the superfile centroid regions instead.
    #[test]
    #[should_panic(expected = "fp32 centroids were dropped")]
    fn transposed_on_stripped_summary_panics() {
        const DIM: usize = 64;
        const ROT_SEED: u64 = 7;
        let mut flat = vec![0.0f32; DIM];
        flat[0] = 1.0;
        let mut cc = ClusterCentroids::from_fp32(1, DIM as u32, &flat, vec![1]);
        cc.strip_centroids_after_slab(
            &RandomRotation::new(DIM, ROT_SEED),
            &BitQuantizer::new(DIM),
            ROT_SEED,
        );
        let _ = cc.transposed();
    }

    /// `score_clusters_into` must match [`distance`] on the fp32 centroid slice.
    #[test]
    fn score_clusters_into_matches_centroid_distance() {
        let (n_cent, dim) = (17u32, 96u32);
        let (cc, centroids) = synth_clusters(n_cent, dim, 7);
        let query: Vec<f32> = (0..dim)
            .map(|j| ((j as u64 * 40_503 + 11) % 997) as f32 / 500.0 - 1.0)
            .collect();

        for metric in [Metric::Cosine, Metric::L2Sq, Metric::NegDot] {
            let mut scored: Vec<(u32, f32)> = Vec::new();
            cc.score_clusters_into(metric, &query, |c, s| {
                scored.push((c, s));
            });

            let mut reference: Vec<(u32, f32)> = Vec::new();
            for c in 0..n_cent as usize {
                if cc.counts[c] == 0 {
                    continue;
                }
                let d = distance(metric, &query, cc.centroid(c));
                // Single-cluster probe must equal the direct distance.
                assert_eq!(
                    cc.score_one(metric, c, &query),
                    d,
                    "{metric:?}: score_one c{c}"
                );
                reference.push((c as u32, d));
            }

            assert_eq!(
                scored.len(),
                reference.len(),
                "{metric:?}: cluster sets differ (count-0 skip)"
            );
            for ((sc, ss), (rc, rs)) in scored.iter().zip(&reference) {
                assert_eq!(sc, rc, "{metric:?}: cluster order");
                assert!(
                    (ss - rs).abs() <= 1e-5 * (1.0 + rs.abs()),
                    "{metric:?} cluster {sc}: {ss} vs {rs}"
                );
            }
        }

        // fp32 storage is lossless: to_fp32 returns the input centroids verbatim.
        let roundtrip = cc.to_fp32();
        for (i, (&got, &want)) in roundtrip.iter().zip(centroids.iter()).enumerate() {
            assert_eq!(got, want, "roundtrip[{i}]: {got} vs {want}");
        }
    }

    /// Microbench: Sq8+ε dequant + distance cluster scoring at supertable scale.
    #[test]
    #[ignore = "perf microbench, not a correctness gate"]
    fn score_clusters_microbench() {
        let (n_cent, dim) = (4096u32, 384u32);
        let iters = 50usize;
        let (cc, _) = synth_clusters(n_cent, dim, 99);
        let query: Vec<f32> = (0..dim).map(|j| (j as f32).sin()).collect();

        for metric in [Metric::Cosine, Metric::L2Sq] {
            let t0 = Instant::now();
            for _ in 0..iters {
                let mut acc = 0f32;
                cc.score_clusters_into(metric, &query, |_, s| acc += s);
                black_box(acc);
            }
            let us = t0.elapsed().as_micros() as f64 / iters as f64;
            println!("score_clusters {metric:?}: {us:.0} µs/query");
        }
    }

    fn schema() -> Arc<Schema> {
        Arc::new(Schema::new(vec![Field::new(
            "title",
            DataType::LargeUtf8,
            false,
        )]))
    }

    fn opts() -> Arc<SupertableOptions> {
        let tk = default_tokenizer();
        Arc::new(
            SupertableOptions::new(
                schema(),
                vec![FtsConfig {
                    column: "title".into(),
                    positions: false,
                }],
                vec![],
                Some(tk),
            )
            .expect("valid options"),
        )
    }

    fn seg_entry(uuid: Uuid, n_docs: u64) -> Arc<SuperfileEntry> {
        Arc::new(SuperfileEntry {
            birth_version: 0,
            superfile_id: uuid,
            uri: SuperfileUri(uuid),
            n_docs,
            id_min: 0,
            id_max: n_docs.saturating_sub(1) as i128,
            scalar_stats: HashMap::new(),
            fts_summary: HashMap::new(),
            vector_summary: HashMap::new(),
            partition_key: Vec::new(),
            partition_hint: None,
            vector_layout: VectorLayout::Ivf,
            subsection_offsets: None,
        })
    }

    #[test]
    fn empty_manifest_starts_at_zero() {
        let m = ManifestSnapshot::empty(opts());
        assert_eq!(m.manifest_id, 0);
        assert_eq!(m.superfiles.len(), 0);
        assert_eq!(m.n_docs_total(), 0);
    }

    #[test]
    fn with_appended_increments_manifest_id_and_extends_superfiles() {
        let m0 = ManifestSnapshot::empty(opts());
        let entry = seg_entry(Uuid::new_v4(), 100);
        let m1 = m0.with_appended(vec![entry.clone()]);
        assert_eq!(m1.manifest_id, 1);
        assert_eq!(m1.superfiles.len(), 1);
        assert_eq!(m1.n_docs_total(), 100);
        // Original m0 unchanged — the immutability invariant.
        assert_eq!(m0.manifest_id, 0);
        assert_eq!(m0.superfiles.len(), 0);
        assert_eq!(m0.n_docs_total(), 0);
    }

    #[test]
    fn with_appended_chains_to_higher_manifest_ids() {
        let m0 = ManifestSnapshot::empty(opts());
        let m1 = m0.with_appended(vec![seg_entry(Uuid::new_v4(), 50)]);
        let m2 = m1.with_appended(vec![seg_entry(Uuid::new_v4(), 75)]);
        assert_eq!(m0.manifest_id, 0);
        assert_eq!(m1.manifest_id, 1);
        assert_eq!(m2.manifest_id, 2);
        assert_eq!(m0.superfiles.len(), 0);
        assert_eq!(m1.superfiles.len(), 1);
        assert_eq!(m2.superfiles.len(), 2);
        assert_eq!(m2.n_docs_total(), 50 + 75);
    }

    #[test]
    fn with_appended_shares_old_superfiles_via_arc() {
        // The new manifest's superfiles[0] should be the SAME Arc as
        // the original's superfiles[0] — copy-on-write doesn't
        // re-allocate per-superfile. (Verified by Arc::ptr_eq.)
        let entry = seg_entry(Uuid::new_v4(), 1);
        let m0 = ManifestSnapshot::empty(opts()).with_appended(vec![entry.clone()]);
        let m1 = m0.with_appended(vec![seg_entry(Uuid::new_v4(), 2)]);
        assert!(Arc::ptr_eq(&m0.superfiles[0], &m1.superfiles[0]));
    }

    #[test]
    fn with_appended_empty_input_still_bumps_manifest_id() {
        // Edge case: with_appended(vec![]) is a no-op for superfiles
        // but should still produce a new manifest_id. (Whether this
        // is a "should" decision or "ok behavior" is fine here —
        // the writer won't call it with empty input in practice;
        // the test pins the current behavior.)
        let m0 = ManifestSnapshot::empty(opts());
        let m1 = m0.with_appended(vec![]);
        assert_eq!(m1.manifest_id, 1);
        assert_eq!(m1.superfiles.len(), 0);
    }

    #[test]
    fn new_from_superfiles_builds_manifest_at_id_one_with_entries() {
        // `new_from_superfiles` is `empty(opts).with_appended(...)`:
        // one append hop off the empty manifest, so manifest_id lands
        // at 1 and the manifest carries exactly the entries handed in.
        let a = seg_entry(Uuid::new_v4(), 10);
        let b = seg_entry(Uuid::new_v4(), 20);
        let m = ManifestSnapshot::new_from_superfiles(opts(), vec![a.clone(), b.clone()]);
        assert_eq!(m.manifest_id, 1);
        assert_eq!(m.superfiles.len(), 2);
        assert_eq!(m.n_docs_total(), 30);
        // Copy-on-write shares the passed-in Arcs rather than
        // re-allocating per-superfile.
        assert!(Arc::ptr_eq(&m.superfiles[0], &a));
        assert!(Arc::ptr_eq(&m.superfiles[1], &b));
        // No storage attached, so it's an in-process-only manifest
        // (no Manifest / loader).
        assert!(m.is_in_process_only());
    }

    #[test]
    fn new_from_superfiles_with_empty_input_is_empty_at_id_one() {
        // Mirrors `with_appended(vec![])`: no superfiles, but the
        // single append hop still advances manifest_id to 1.
        let m = ManifestSnapshot::new_from_superfiles(opts(), vec![]);
        assert_eq!(m.manifest_id, 1);
        assert_eq!(m.superfiles.len(), 0);
        assert_eq!(m.n_docs_total(), 0);
    }

    #[test]
    fn get_next_manifest_id_is_current_plus_one() {
        let m0 = ManifestSnapshot::empty(opts());
        assert_eq!(m0.get_manifest_id(), 0);
        assert_eq!(m0.get_next_manifest_id(), 1);

        let m1 = m0.with_appended(vec![seg_entry(Uuid::new_v4(), 1)]);
        assert_eq!(m1.get_manifest_id(), 1);
        assert_eq!(m1.get_next_manifest_id(), 2);
    }

    #[test]
    fn get_next_manifest_id_is_a_pure_read() {
        // Querying the successor id is side-effect-free: the
        // manifest's own id is untouched and repeat calls are stable.
        let m = ManifestSnapshot::empty(opts());
        let _ = m.get_next_manifest_id();
        assert_eq!(m.get_manifest_id(), 0, "current id unchanged");
        assert_eq!(m.get_next_manifest_id(), m.get_next_manifest_id());
    }

    #[test]
    fn superfile_uri_is_distinct_per_call() {
        let a = SuperfileUri::new_v4();
        let b = SuperfileUri::new_v4();
        assert_ne!(a, b);
    }

    // ============================================================
    // In-memory `ManifestSnapshot` with lazy-load parts — content-hash-
    // verified per-part fetch through an injected
    // `StorageProvider`, OnceCell coalescing on cold cells,
    // typed errors for missing loader / missing part / hash
    // mismatch.
    // ============================================================

    mod lazy_load {
        use std::{
            collections::HashMap,
            error::Error,
            ops::Range,
            slice::from_ref,
            sync::{
                Arc,
                atomic::{AtomicUsize, Ordering},
            },
            time::SystemTime,
        };

        use arrow_schema::{DataType, Field, Schema};
        use async_trait::async_trait;
        use bytes::Bytes;
        use dashmap::DashMap;
        use tokio::spawn;
        use uuid::Uuid;

        use super::super::*;
        use crate::{
            storage::{ObjectMeta, StorageError, StorageProvider},
            supertable::{
                SupertableOptions,
                manifest::{
                    list::{FORMAT_VERSION as LIST_FORMAT_VERSION, Manifest, PartitionStrategy},
                    part::{self as part_mod, ContentHash, ManifestPart, PartId},
                },
            },
        };

        #[derive(Debug)]
        struct CountingMockStorage {
            objects: HashMap<String, Bytes>,
            get_calls: AtomicUsize,
        }

        impl CountingMockStorage {
            fn new(objects: HashMap<String, Bytes>) -> Self {
                Self {
                    objects,
                    get_calls: AtomicUsize::new(0),
                }
            }

            fn get_call_count(&self) -> usize {
                self.get_calls.load(Ordering::Acquire)
            }
        }

        #[async_trait]
        impl StorageProvider for CountingMockStorage {
            async fn head(&self, uri: &str) -> Result<ObjectMeta, StorageError> {
                match self.objects.get(uri) {
                    Some(b) => Ok(ObjectMeta {
                        size: b.len() as u64,
                        etag: Some("mock-etag".into()),
                        last_modified: SystemTime::UNIX_EPOCH,
                    }),
                    None => Err(StorageError::NotFound { uri: uri.into() }),
                }
            }

            async fn get(&self, uri: &str) -> Result<(Bytes, ObjectMeta), StorageError> {
                self.get_calls.fetch_add(1, Ordering::AcqRel);
                match self.objects.get(uri) {
                    Some(b) => Ok((
                        b.clone(),
                        ObjectMeta {
                            size: b.len() as u64,
                            etag: Some("mock-etag".into()),
                            last_modified: SystemTime::UNIX_EPOCH,
                        },
                    )),
                    None => Err(StorageError::NotFound { uri: uri.into() }),
                }
            }

            async fn get_range(
                &self,
                uri: &str,
                _range: Range<u64>,
            ) -> Result<Bytes, StorageError> {
                Err(permanent(uri, "get_range unimplemented for mock"))
            }

            async fn put_atomic(
                &self,
                uri: &str,
                _bytes: Bytes,
            ) -> Result<Option<String>, StorageError> {
                Err(permanent(uri, "put_atomic unimplemented for mock"))
            }

            async fn put_if_match(
                &self,
                uri: &str,
                _bytes: Bytes,
                _expected_etag: Option<&str>,
            ) -> Result<Option<String>, StorageError> {
                Err(permanent(uri, "put_if_match unimplemented for mock"))
            }

            async fn put_multipart(
                &self,
                uri: &str,
            ) -> Result<Box<dyn object_store::MultipartUpload>, StorageError> {
                Err(permanent(uri, "put_multipart unimplemented for mock"))
            }

            async fn delete(&self, _uri: &str) -> Result<(), StorageError> {
                Ok(())
            }
        }

        fn permanent(uri: &str, msg: &'static str) -> StorageError {
            let boxed: Box<dyn Error + Send + Sync> = msg.into();
            StorageError::Permanent {
                uri: uri.into(),
                source: boxed,
            }
        }

        fn make_test_part(seed: u8) -> ManifestPart {
            ManifestPart {
                format_version: part_mod::FORMAT_VERSION.into(),
                part_id: PartId(Uuid::from_bytes([seed; 16])),
                superfiles: vec![],
            }
        }

        fn encode_and_index(
            parts: &[ManifestPart],
        ) -> (HashMap<String, Bytes>, Vec<ManifestPartEntry>) {
            let mut objects = HashMap::new();
            let mut entries = Vec::new();
            for p in parts {
                let bytes = part_mod::encode(p);
                let hash = ContentHash::of(&bytes);
                let uri = format!("manifests/part-{}.avro.zst", hash.to_hex());
                let size_compressed = bytes.len() as u64;
                objects.insert(uri.clone(), Bytes::from(bytes));
                entries.push(ManifestPartEntry {
                    part_id: p.part_id,
                    uri,
                    n_superfiles: p.superfiles.len() as u64,
                    size_bytes_compressed: size_compressed,
                    size_bytes_uncompressed: size_compressed,
                    content_hash: hash,
                    routing: None,
                    id_range: (0, 0),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                });
            }
            (objects, entries)
        }

        fn fresh_list(entries: Vec<ManifestPartEntry>) -> Manifest {
            Manifest {
                drained_ranges: Default::default(),
                global_vector_index: None,
                tombstone_seqs: Default::default(),
                format_version: LIST_FORMAT_VERSION.into(),
                manifest_id: 1,
                options_hash: ContentHash([0u8; 32]),
                schema: Vec::new(),
                id_column: "doc_id".into(),
                fts_columns: vec![],
                vector_columns: vec![],
                partition_strategy: PartitionStrategy::Hash {
                    column: "doc_id".into(),
                    n_buckets: 64,
                },
                vector_index_storage_prefix: None,
                deleted_user_ids_inline: None,
                slow_vector_state_uri: None,
                slow_vector_state_content_hash: None,
                slow_vector_state_centroids: None,
                parts: entries,
            }
        }

        fn options_for_test() -> Arc<SupertableOptions> {
            let s = Arc::new(Schema::new(vec![Field::new(
                "title",
                DataType::LargeUtf8,
                false,
            )]));
            Arc::new(SupertableOptions::new(s, vec![], vec![], None).expect("opts"))
        }

        fn build_manifest_with_loader(
            list: Manifest,
            storage: Arc<dyn StorageProvider>,
        ) -> ManifestSnapshot {
            let loader = Arc::new(ManifestPartLoader::new(Arc::clone(&storage), &list));
            ManifestSnapshot {
                superfile_list: SuperfileList::empty(options_for_test()),
                list: Some(list),
                parts: DashMap::new(),
                loader: Some(loader),
                stamped_partition_strategy: None,
                stamped_global_vector_index: None,
                stamped_drained_ranges: None,
            }
        }

        #[tokio::test]
        async fn part_first_touch_loads_and_caches() {
            let part = make_test_part(7);
            let (objects, entries) = encode_and_index(from_ref(&part));
            let storage = Arc::new(CountingMockStorage::new(objects));
            let list = fresh_list(entries);
            let manifest =
                build_manifest_with_loader(list, Arc::clone(&storage) as Arc<dyn StorageProvider>);

            let loaded = manifest.get_part_by_id(part.part_id).await.expect("load");
            assert_eq!(loaded.part_id, part.part_id);
            assert_eq!(storage.get_call_count(), 1, "exactly one storage.get");
        }

        #[tokio::test]
        async fn second_touch_hits_cache_zero_additional_gets() {
            let part = make_test_part(11);
            let (objects, entries) = encode_and_index(from_ref(&part));
            let storage = Arc::new(CountingMockStorage::new(objects));
            let list = fresh_list(entries);
            let manifest =
                build_manifest_with_loader(list, Arc::clone(&storage) as Arc<dyn StorageProvider>);

            let a = manifest
                .get_part_by_id(part.part_id)
                .await
                .expect("first load");
            let b = manifest
                .get_part_by_id(part.part_id)
                .await
                .expect("second load");
            assert!(Arc::ptr_eq(&a, &b), "second touch must return cached Arc");
            assert_eq!(storage.get_call_count(), 1, "cache hit ⇒ no extra get");
        }

        #[tokio::test]
        async fn concurrent_loaders_coalesce_to_one_get() {
            let part = make_test_part(13);
            let (objects, entries) = encode_and_index(from_ref(&part));
            let storage = Arc::new(CountingMockStorage::new(objects));
            let list = fresh_list(entries);
            let manifest = Arc::new(build_manifest_with_loader(
                list,
                Arc::clone(&storage) as Arc<dyn StorageProvider>,
            ));

            // 100 concurrent tasks on the same cold cell.
            let mut handles = Vec::with_capacity(100);
            for _ in 0..100 {
                let m = Arc::clone(&manifest);
                let pid = part.part_id;
                handles.push(spawn(async move { m.get_part_by_id(pid).await }));
            }
            let mut first: Option<Arc<ManifestPart>> = None;
            for h in handles {
                let p = h.await.expect("join").expect("load");
                match &first {
                    None => first = Some(p),
                    Some(f) => assert!(
                        Arc::ptr_eq(f, &p),
                        "all concurrent loaders must share the same Arc"
                    ),
                }
            }
            assert_eq!(
                storage.get_call_count(),
                1,
                "100 concurrent loaders on cold cell ⇒ exactly one storage.get"
            );
        }

        #[tokio::test]
        async fn content_hash_mismatch_surfaces_typed_error_without_refetch() {
            let part = make_test_part(17);
            let (mut objects, entries) = encode_and_index(from_ref(&part));
            // Tamper with the stored bytes — content_hash on
            // the list entry no longer matches.
            let bytes = objects.values().next().expect("one obj").clone();
            let mut tampered = bytes.to_vec();
            let last = tampered.len() - 1;
            tampered[last] ^= 0xff;
            let uri = entries[0].uri.clone();
            objects.insert(uri, Bytes::from(tampered));
            let (_, fresh_entries) = encode_and_index(from_ref(&part));
            let list = fresh_list(fresh_entries);

            let storage = Arc::new(CountingMockStorage::new(objects));
            let manifest =
                build_manifest_with_loader(list, Arc::clone(&storage) as Arc<dyn StorageProvider>);

            let err = manifest
                .get_part_by_id(part.part_id)
                .await
                .expect_err("must reject tampered bytes");
            assert!(
                matches!(err, ManifestLoadError::ContentHashMismatch { .. }),
                "expected ContentHashMismatch, got {err:?}"
            );
            // Bad bytes are NOT auto-refetched. Retry returns
            // the same error. OnceCell behavior on Err futures
            // is implementation-defined (cached vs re-issued);
            // load-bearing assertion is just that retry does
            // not magically succeed.
            let _pre = storage.get_call_count();
            let err2 = manifest
                .get_part_by_id(part.part_id)
                .await
                .expect_err("must reject on retry too");
            assert!(matches!(
                err2,
                ManifestLoadError::ContentHashMismatch { .. }
            ));
        }

        #[tokio::test]
        async fn part_id_not_in_list_surfaces_typed_error() {
            let part = make_test_part(19);
            let (objects, entries) = encode_and_index(&[part]);
            let storage = Arc::new(CountingMockStorage::new(objects));
            let list = fresh_list(entries);
            let manifest =
                build_manifest_with_loader(list, Arc::clone(&storage) as Arc<dyn StorageProvider>);

            let stranger = PartId(Uuid::from_bytes([0xff; 16]));
            let err = manifest
                .get_part_by_id(stranger)
                .await
                .expect_err("must reject");
            assert!(
                matches!(err, ManifestLoadError::PartNotInList { .. }),
                "expected PartNotInList, got {err:?}"
            );
            assert_eq!(
                storage.get_call_count(),
                0,
                "missing-id check happens before any storage.get"
            );
        }

        #[tokio::test]
        async fn disk_cache_hit_serves_second_loader_without_storage_get() {
            // Two independent loaders sharing one on-disk manifest cache
            // (models a fresh manifest snapshot, or a process restart):
            // the first populates the cache from storage, the second
            // reads the part bytes off local disk with zero storage GETs.
            let part = make_test_part(23);
            let (objects, entries) = encode_and_index(from_ref(&part));
            let storage = Arc::new(CountingMockStorage::new(objects));
            let storage_dyn = Arc::clone(&storage) as Arc<dyn StorageProvider>;
            let list = fresh_list(entries);

            let cache_root = std::env::temp_dir()
                .join("infino-manifest-cache-loader-test-disk_cache_hit_second_loader");
            let _ = std::fs::remove_dir_all(&cache_root);
            let cache = ManifestDiskCache::new(cache_root.clone(), 1 << 20).expect("cache");

            // Loader A: cold — one storage GET, cache populated.
            let loader_a = ManifestPartLoader::new_with_cache(
                Arc::clone(&storage_dyn),
                &list,
                Some(Arc::clone(&cache)),
            );
            let a = loader_a.load(part.part_id).await.expect("first load");
            assert_eq!(a.part_id, part.part_id);
            assert_eq!(storage.get_call_count(), 1, "first loader fetches once");
            assert_eq!(cache.stats().n_entries, 1, "part bytes cached on disk");

            // Loader B: fresh loader, same cache — disk hit, no new GET.
            let loader_b = ManifestPartLoader::new_with_cache(
                Arc::clone(&storage_dyn),
                &list,
                Some(Arc::clone(&cache)),
            );
            let b = loader_b.load(part.part_id).await.expect("second load");
            assert_eq!(b.part_id, part.part_id);
            assert_eq!(
                storage.get_call_count(),
                1,
                "disk-cache hit ⇒ no additional storage.get"
            );
            assert!(cache.stats().n_hits >= 1, "recorded a cache hit");

            let _ = std::fs::remove_dir_all(&cache_root);
        }

        #[tokio::test]
        async fn loader_without_cache_always_hits_storage() {
            // Sanity: with no cache attached, each loader load is a
            // storage GET — confirms the cache is what removes them.
            let part = make_test_part(29);
            let (objects, entries) = encode_and_index(from_ref(&part));
            let storage = Arc::new(CountingMockStorage::new(objects));
            let storage_dyn = Arc::clone(&storage) as Arc<dyn StorageProvider>;
            let list = fresh_list(entries);

            let loader = ManifestPartLoader::new(Arc::clone(&storage_dyn), &list);
            loader.load(part.part_id).await.expect("load 1");
            loader.load(part.part_id).await.expect("load 2");
            assert_eq!(
                storage.get_call_count(),
                2,
                "no cache ⇒ every load round-trips to storage"
            );
        }

        #[tokio::test]
        async fn no_loader_attached_surfaces_typed_error() {
            // In-process-only manifest — ManifestSnapshot::empty has
            // no loader. Calling part() must error cleanly,
            // not panic.
            let manifest = ManifestSnapshot::empty(options_for_test());
            let err = manifest
                .get_part_by_id(PartId(Uuid::nil()))
                .await
                .expect_err("must error");
            assert!(
                matches!(err, ManifestLoadError::NoLoaderAttached),
                "expected NoLoaderAttached, got {err:?}"
            );
        }
    }

    // ============================================================
    // SuperfileUri path helpers, Debug formatters, and the
    // `add_sum_arrays` additive-sum helper (the scalar-stats build /
    // merge logic itself is tested on `ScalarStatsAgg` in `list.rs`).
    // ============================================================

    #[test]
    fn superfile_uri_path_helpers_share_the_same_uuid() {
        let uri = SuperfileUri(Uuid::from_u128(0x1234_5678));
        let id = uri.0;
        assert_eq!(uri.storage_path(), format!("data/seg-{id}.sf.parquet"));
        assert_eq!(uri.cache_filename(), format!("seg-{id}.sf.parquet"));
        assert_eq!(uri.cache_tmp_filename(), format!("seg-{id}.sf.parquet.tmp"));
    }

    #[test]
    fn manifest_debug_reports_counts() {
        let m = ManifestSnapshot::empty(opts()).with_appended(vec![seg_entry(Uuid::new_v4(), 3)]);
        let dbg = format!("{m:?}");
        assert!(dbg.contains("ManifestSnapshot"));
        assert!(dbg.contains("manifest_id"));
        assert!(dbg.contains("n_superfiles"));
        // No storage attached ⇒ has_loader false, has_list false.
        assert!(dbg.contains("has_loader"));
    }

    #[test]
    fn manifest_debug_with_list_reports_part_count() {
        // A ManifestSnapshot carrying a `list` exercises the Some-arm of the
        // `n_parts` closure in Debug (the empty-ManifestSnapshot test above
        // only hits the `unwrap_or(0)` None-arm).
        use list::{Manifest, PartitionStrategy};
        let entry = part::PartId::new_v4();
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 1,
            options_hash: part::ContentHash([0u8; 32]),
            schema: Vec::new(),
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![list::ManifestPartEntry {
                part_id: entry,
                uri: "manifests/part-x".into(),
                n_superfiles: 0,
                size_bytes_compressed: 0,
                size_bytes_uncompressed: 0,
                content_hash: part::ContentHash([0u8; 32]),
                routing: None,
                id_range: (0, 0),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let m = ManifestSnapshot {
            superfile_list: SuperfileList::empty(opts()),
            list: Some(list),
            parts: DashMap::new(),
            loader: None,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        };
        let dbg = format!("{m:?}");
        assert!(dbg.contains("n_parts: 1"), "{dbg}");
        assert!(dbg.contains("has_list: true"), "{dbg}");
    }

    #[test]
    fn cluster_centroids_empty_is_empty_and_default_matches() {
        let cc = ClusterCentroids::empty();
        assert!(cc.is_empty());
        assert_eq!(cc.n_cent, 0);
        // A populated one is not empty.
        let cc = ClusterCentroids::from_fp32(2, 4, &[0.0; 8], vec![1, 1]);
        assert!(!cc.is_empty());
        assert_eq!(cc.n_cent, 2);
        assert_eq!(cc.dim, 4);
    }

    #[test]
    fn add_sum_arrays_handles_each_type_and_overflow() {
        use arrow_array::{Float64Array, Int64Array, UInt64Array};
        // Int64 + Int64.
        let r = add_sum_arrays(
            &(Arc::new(Int64Array::from(vec![3])) as ArrayRef),
            &(Arc::new(Int64Array::from(vec![4])) as ArrayRef),
        )
        .expect("int sum");
        assert_eq!(
            r.as_any()
                .downcast_ref::<Int64Array>()
                .expect("test")
                .value(0),
            7
        );
        // UInt64 + UInt64.
        let r = add_sum_arrays(
            &(Arc::new(UInt64Array::from(vec![3u64])) as ArrayRef),
            &(Arc::new(UInt64Array::from(vec![4u64])) as ArrayRef),
        )
        .expect("uint sum");
        assert_eq!(
            r.as_any()
                .downcast_ref::<UInt64Array>()
                .expect("test")
                .value(0),
            7
        );
        // Float64 + Float64.
        let r = add_sum_arrays(
            &(Arc::new(Float64Array::from(vec![1.5])) as ArrayRef),
            &(Arc::new(Float64Array::from(vec![2.5])) as ArrayRef),
        )
        .expect("float sum");
        assert!(
            (r.as_any()
                .downcast_ref::<Float64Array>()
                .expect("test")
                .value(0)
                - 4.0)
                .abs()
                < 1e-9
        );
        // Overflow → None.
        let r = add_sum_arrays(
            &(Arc::new(Int64Array::from(vec![i64::MAX])) as ArrayRef),
            &(Arc::new(Int64Array::from(vec![1])) as ArrayRef),
        );
        assert!(r.is_none(), "i64 overflow drops the stat");
        // Type mismatch → None.
        let r = add_sum_arrays(
            &(Arc::new(Int64Array::from(vec![1])) as ArrayRef),
            &(Arc::new(UInt64Array::from(vec![1u64])) as ArrayRef),
        );
        assert!(r.is_none(), "type mismatch drops the stat");
    }

    // ---- ManifestSnapshot::update-------------------------------------------
    /// Base builder for a synthetic superfile entry. `pk` is the on-disk
    /// `partition_key`: pass a stamped key to model a prior-commit entry (as
    /// stored in an existing part), or `Vec::new()` for an unstamped entry
    /// destined for `update()`, which derives and stamps the key itself.
    fn make_entry(docs: u64, pk: Vec<u8>, hint: Option<u32>) -> Arc<SuperfileEntry> {
        Arc::new(SuperfileEntry {
            birth_version: 0,
            superfile_id: uuid::Uuid::new_v4(),
            uri: SuperfileUri::new_v4(),
            n_docs: docs,
            id_min: 0,
            id_max: docs as i128 - 1,
            scalar_stats: Default::default(),
            fts_summary: Default::default(),
            vector_summary: Default::default(),
            partition_key: pk,
            partition_hint: hint,
            vector_layout: VectorLayout::Ivf,
            subsection_offsets: None,
        })
    }

    /// Stamped prior-commit entry (non-empty `partition_key`), for placing
    /// into existing on-disk parts.
    fn make_superfile_entry(docs: u64, pk: Vec<u8>) -> Arc<SuperfileEntry> {
        make_entry(docs, pk, None)
    }

    /// Builds an UNSTAMPED entry (empty partition_key) for passing to
    /// `update()`, which derives and stamps the key. Entries that model a
    /// prior commit (placed into existing parts) keep `make_superfile_entry*`,
    /// which carries the already-stamped key.
    fn make_new_entry(docs: u64) -> Arc<SuperfileEntry> {
        make_entry(docs, Vec::new(), None)
    }

    fn hash_bucket_0_pk() -> Vec<u8> {
        // Hash partition with n_buckets=1 encodes to [0, 0, 0, 0] in little-endian
        vec![0, 0, 0, 0]
    }

    fn simple_schema() -> Arc<Schema> {
        Arc::new(Schema::new(vec![Field::new(
            "text",
            DataType::LargeUtf8,
            false,
        )]))
    }

    fn make_opts() -> Arc<SupertableOptions> {
        SupertableOptions::new(simple_schema(), vec![], vec![], None)
            .map(Arc::new)
            .expect("valid options")
    }

    fn empty_manifest(opts: &Arc<SupertableOptions>) -> Arc<ManifestSnapshot> {
        Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList::empty(opts.clone()),
            list: Some(Manifest {
                drained_ranges: Default::default(),
                global_vector_index: None,
                tombstone_seqs: Default::default(),
                format_version: list::FORMAT_VERSION.into(),
                manifest_id: 0,
                options_hash: ContentHash([0u8; 32]),
                schema: vec![],
                id_column: "_id".into(),
                fts_columns: vec![],
                vector_columns: vec![],
                partition_strategy: PartitionStrategy::Hash {
                    column: "_id".into(),
                    n_buckets: 1,
                },
                vector_index_storage_prefix: None,
                deleted_user_ids_inline: None,
                slow_vector_state_uri: None,
                slow_vector_state_content_hash: None,
                slow_vector_state_centroids: None,
                parts: vec![],
            }),
            parts: DashMap::new(),
            loader: None,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        })
    }

    /// Slow-CAS section semantics: `with_slow_vector_state` stamps the ref
    /// (bumping manifest_id, preserving membership); `update` — the
    /// membership-change path — CLEARS it in the successor list; the
    /// deleted-ids stamper preserves it (list-only churn keeps residency).
    #[tokio::test]
    async fn slow_vector_state_ref_stamp_clear_and_preserve() {
        let opts = make_opts();
        let manifest = empty_manifest(&opts);
        assert!(manifest.slow_vector_state_blob().is_none());

        let hash = ContentHash([3u8; 32]);
        let centroids = RoutingRef {
            uri: "slow-vector-state/state-c.bin".into(),
            content_hash: ContentHash([5u8; 32]),
        };
        let stamped = manifest.with_slow_vector_state(
            "slow-vector-state/state-x.bin".into(),
            hash,
            centroids.clone(),
        );
        let (uri, got_hash) = stamped.slow_vector_state_blob().expect("ref stamped");
        assert_eq!(uri, "slow-vector-state/state-x.bin");
        assert_eq!(got_hash, hash);
        assert_eq!(
            stamped.slow_vector_state_centroids_blob(),
            Some(&centroids),
            "centroid-section sibling stamped with the state ref"
        );
        assert_eq!(stamped.get_manifest_id(), manifest.get_next_manifest_id());
        assert_eq!(
            stamped.get_all_superfiles().len(),
            manifest.get_all_superfiles().len(),
            "stamp must not change membership"
        );

        // A deleted-ids stamp (list-only churn: the user-delete path) must
        // NOT disturb the slow-state ref — this is the residency invariant.
        let deleted_stamped = stamped.with_deleted_user_ids(Vec::new());
        assert!(
            deleted_stamped.slow_vector_state_blob().is_some(),
            "deleted-ids stamp must preserve the slow-state ref"
        );
        assert!(
            deleted_stamped.slow_vector_state_centroids_blob().is_some(),
            "deleted-ids stamp must preserve the centroid-section ref"
        );

        // A membership change (update) must CLEAR the ref: the blob no
        // longer describes the new membership; only maintenance restamps.
        let new_entry = make_new_entry(100);
        let (updated, _parts) = stamped
            .update(from_ref(&new_entry), &[])
            .await
            .expect("update");
        assert!(
            updated.slow_vector_state_blob().is_none(),
            "membership change must clear the slow-state ref"
        );
        assert!(
            updated.slow_vector_state_centroids_blob().is_none(),
            "membership change must clear the centroid-section ref"
        );
    }

    /// A manifest whose list carries a slow-state ref hydrated its
    /// membership from the blob — hidden manifests write NO parts. The
    /// undrained load must trust the resident flat view there: summing
    /// `parts[].n_superfiles` gives zero, and the part fan it used to
    /// trigger flattened zero parts into zero entries, silently dropping
    /// every undrained superfile.
    #[tokio::test]
    async fn undrained_load_trusts_resident_view_with_slow_state_ref() {
        let opts = make_opts();
        let entries = vec![
            make_superfile_entry(100, hash_bucket_0_pk()),
            make_superfile_entry(50, hash_bucket_0_pk()),
        ];
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 1,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: Some("slow-vector-state/state-abc.bin".into()),
            slow_vector_state_content_hash: Some(ContentHash([7u8; 32])),
            slow_vector_state_centroids: None,
            parts: Vec::new(),
        };
        // Storage must be attached: `new` only keeps the list (and builds
        // the part loader this test's fan path needs) when it is.
        let (_dir, storage) = local_storage();
        let manifest = ManifestSnapshot::new(1, opts, entries.clone(), Some(storage), Some(list));
        let drained = list::DrainedVersionRanges::default();
        let got = manifest
            .get_undrained_superfiles_loaded(&drained)
            .await
            .expect("undrained load");
        assert_eq!(
            got.len(),
            entries.len(),
            "resident blob-hydrated membership must be returned, not the empty part fan"
        );
    }

    #[tokio::test]
    async fn update_fresh_start_cold_partition_should_create_entry() {
        let opts = make_opts();
        let old_manifest = empty_manifest(&opts);

        let new_entry = make_new_entry(100);
        let new_entries = vec![new_entry];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);
        assert_eq!(list_entries[0].n_superfiles, 1);
        assert_eq!(parts[0].part.superfiles.len(), 1);
        assert_eq!(parts[0].part.superfiles[0].n_docs, 100);
    }

    #[tokio::test]
    async fn update_fresh_start_multiple_cold_partitions_should_create_entries() {
        // Multiple new entries in a single commit all land in one table-level
        // part (well under the default target).
        let opts = make_opts();
        let old_manifest = empty_manifest(&opts);

        let entry1 = make_new_entry(100);
        let entry2 = make_new_entry(200);
        let new_entries = vec![entry1, entry2];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);
        assert_eq!(list_entries[0].n_superfiles, 2);
        assert_eq!(parts[0].part.superfiles.len(), 2);
        let total_docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 300);
    }

    fn local_storage() -> (TempDir, Arc<dyn StorageProvider>) {
        let dir = TempDir::new().expect("tempdir");
        let store: Arc<dyn StorageProvider> =
            Arc::new(LocalFsStorageProvider::new(dir.path()).expect("local"));
        (dir, store)
    }

    /// Number of parts whose `OnceCell` actually holds decoded bytes —
    /// distinct from `get_num_parts_loaded()`, which counts map slots (the
    /// lazy and hydrated branches pre-insert empty cells for every part).
    fn n_parts_initialized(m: &ManifestSnapshot) -> usize {
        m.parts
            .iter()
            .filter(|kv| kv.value().get().is_some())
            .count()
    }

    /// Persist one part (two entries) + a list referencing it + the pointer.
    /// `slow_ref` optionally stamps the list's slow-CAS section, letting the
    /// hydration tests choose a valid ref, a corrupt one, or none.
    async fn persist_two_entry_table(
        storage: &Arc<dyn StorageProvider>,
        slow_ref: Option<(String, ContentHash)>,
    ) -> Vec<Arc<SuperfileEntry>> {
        let entries = vec![
            make_superfile_entry(100, hash_bucket_0_pk()),
            make_superfile_entry(50, hash_bucket_0_pk()),
        ];
        let part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: entries.clone(),
        };
        let pw = write_manifest_part(storage.as_ref(), &part)
            .await
            .expect("write part");
        let (slow_uri, slow_hash) = match slow_ref {
            Some((u, h)) => (Some(u), Some(h)),
            None => (None, None),
        };
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 1,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: slow_uri,
            slow_vector_state_content_hash: slow_hash,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 99),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let lw = write_manifest(storage.as_ref(), &list)
            .await
            .expect("write list");
        write_pointer(
            storage.as_ref(),
            &PointerFile {
                manifest_id: 1,
                manifest_uri: lw.uri,
                content_hash: lw.content_hash,
            },
            None,
        )
        .await
        .expect("write pointer");
        entries
    }

    /// Hydration: a list carrying a verified slow-state ref builds the flat
    /// view from the blob with ZERO part loads; the parts stay lazily
    /// loadable for maintenance.
    #[tokio::test]
    async fn load_hydrates_flat_view_from_slow_state_blob() {
        let opts = make_opts();
        let (_dir, storage) = local_storage();
        let entries = vec![
            make_superfile_entry(100, hash_bucket_0_pk()),
            make_superfile_entry(50, hash_bucket_0_pk()),
        ];
        let published = slow_vector_state::write_state(storage.as_ref(), &entries, None)
            .await
            .expect("write blob");
        let (blob_uri, blob_hash) = (published.uri, published.content_hash);
        // Rebuild the same membership durably with the ref stamped.
        let (_dir2, storage2) = local_storage();
        let _ = _dir2;
        drop(storage2); // single-storage test; helper writes to `storage`.
        let persisted = persist_two_entry_table(&storage, Some((blob_uri, blob_hash))).await;

        let loaded = ManifestSnapshot::load(None, Arc::clone(&storage), Some(opts))
            .await
            .expect("load");
        assert_eq!(loaded.superfiles.len(), 2);
        let want: HashSet<Uuid> = persisted.iter().map(|e| e.superfile_id).collect();
        let got: HashSet<Uuid> = loaded.superfiles.iter().map(|e| e.superfile_id).collect();
        assert_eq!(
            got.len(),
            2,
            "blob-hydrated flat view must carry both entries"
        );
        assert_eq!(want.len(), 2);
        assert_eq!(
            n_parts_initialized(&loaded),
            0,
            "hydration must not fetch any manifest part"
        );
        assert!(loaded.slow_vector_state_blob().is_some());
    }

    /// Dim for the routing-hydration fixture summaries.
    const ROUTING_TEST_DIM: usize = 16;
    /// Rot seed for the routing-hydration fixture slabs.
    const ROUTING_TEST_ROT_SEED: u64 = 5;

    /// Stamped entry carrying a one-cell vector summary whose admit slab is
    /// built — the shape drain-published entries have at republish time.
    fn make_summary_entry(docs: u64) -> Arc<SuperfileEntry> {
        let base = make_superfile_entry(docs, hash_bucket_0_pk());
        let mut entry = (*base).clone();
        let mut flat = vec![0.0f32; 2 * ROUTING_TEST_DIM];
        flat[0] = 1.0;
        flat[ROUTING_TEST_DIM + 1] = -1.0;
        let clusters = ClusterCentroids::from_fp32(2, ROUTING_TEST_DIM as u32, &flat, vec![3, 4]);
        clusters.prewarm_admit_codes(
            &RandomRotation::new(ROUTING_TEST_DIM, ROUTING_TEST_ROT_SEED),
            &BitQuantizer::new(ROUTING_TEST_DIM),
            ROUTING_TEST_ROT_SEED,
        );
        entry.vector_summary.insert(
            "emb".into(),
            VectorSummary {
                centroid: vec![0.5; ROUTING_TEST_DIM],
                cells: vec![CellVectorSummary {
                    cell_id: Some(0),
                    clusters,
                }],
            },
        );
        Arc::new(entry)
    }

    /// Two-object slow-CAS model: the state blob is routing-shaped, so
    /// EVERY consumer — knob on or off — hydrates stripped entries (no
    /// fp32) with the write-time slab seeded; exact centroid scores come
    /// from the published section. The fixture options carry no vector
    /// columns, so the hydration-time strip pass is inert — stripped
    /// entries can only have come from the blob's wire form itself.
    #[tokio::test]
    async fn state_blob_hydrates_stripped_for_all_consumers() {
        let (_dir, storage) = local_storage();
        let entries = vec![make_summary_entry(100), make_summary_entry(50)];
        let published = slow_vector_state::write_state(storage.as_ref(), &entries, None)
            .await
            .expect("write blobs");
        persist_two_entry_table(
            &storage,
            Some((published.uri.clone(), published.content_hash)),
        )
        .await;

        let consumer_opts = |knob: bool| {
            Arc::new(
                SupertableOptions::new(simple_schema(), vec![], vec![], None)
                    .expect("valid options")
                    .with_summary_centroids_from_superfiles(knob),
            )
        };
        let resident = |m: &ManifestSnapshot| {
            m.superfiles
                .iter()
                .map(|e| {
                    let clusters = &e.vector_summary["emb"].cells[0].clusters;
                    assert!(clusters.admit_codes_built().is_some(), "slab always rides");
                    clusters.vectors_resident()
                })
                .collect::<Vec<bool>>()
        };

        let knob_on = ManifestSnapshot::load(None, Arc::clone(&storage), Some(consumer_opts(true)))
            .await
            .expect("knob-on load");
        assert_eq!(
            resident(&knob_on),
            vec![false, false],
            "the routing-shaped state blob hydrates stripped entries"
        );

        let knob_off =
            ManifestSnapshot::load(None, Arc::clone(&storage), Some(consumer_opts(false)))
                .await
                .expect("knob-off load");
        assert_eq!(
            resident(&knob_off),
            vec![false, false],
            "knob-off hydrates the same routing-shaped blob — fp32 lives in the section"
        );
    }

    /// Persist a one-part table whose entries carry vector summaries. The
    /// part ships in both wire forms; `with_routing` controls whether the
    /// list entry stamps the sibling ref (absent models a pre-sibling
    /// manifest). No slow-state ref, so hydration goes through the part
    /// loader — the user-table shape.
    async fn persist_summary_part_table(storage: &Arc<dyn StorageProvider>, with_routing: bool) {
        let entries = vec![make_summary_entry(100), make_summary_entry(50)];
        let part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: entries,
        };
        let full = part::encode(&part);
        let full_hash = ContentHash::of(&full);
        let routing = part::encode_with_mode(&part, SummaryWireMode::RoutingOnly);
        let routing_hash = ContentHash::of(&routing);
        assert!(
            routing.len() < full.len(),
            "routing part must shed the fp32 payload ({} vs {} bytes)",
            routing.len(),
            full.len()
        );
        write_part_bytes(storage.as_ref(), &full)
            .await
            .expect("put full part");
        write_part_bytes(storage.as_ref(), &routing)
            .await
            .expect("put routing part");
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 1,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: part.part_id,
                uri: part_uri(&full_hash),
                content_hash: full_hash,
                routing: with_routing.then(|| RoutingRef {
                    uri: part_uri(&routing_hash),
                    content_hash: routing_hash,
                }),
                size_bytes_compressed: full.len() as u64,
                size_bytes_uncompressed: full.len() as u64,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let lw = write_manifest(storage.as_ref(), &list)
            .await
            .expect("write list");
        write_pointer(
            storage.as_ref(),
            &PointerFile {
                manifest_id: 1,
                manifest_uri: lw.uri,
                content_hash: lw.content_hash,
            },
            None,
        )
        .await
        .expect("write pointer");
    }

    /// The user-table shape (no slow-state ref, hydration through the part
    /// loader): consumer memory mode loads each part's routing sibling —
    /// summaries arrive stripped with the write-time slab, without
    /// downloading the fp32 payload. Knob-off loads (writers) and knob-on
    /// loads of pre-sibling manifests keep the full part. The fixture
    /// options carry no vector columns, so the strip pass is inert and a
    /// stripped summary can only have come from the routing part.
    #[tokio::test]
    async fn consumer_mode_hydrates_parts_from_routing_sibling() {
        let consumer_opts = |knob: bool| {
            Arc::new(
                SupertableOptions::new(simple_schema(), vec![], vec![], None)
                    .expect("valid options")
                    .with_summary_centroids_from_superfiles(knob),
            )
        };
        // (fp32 resident, slab present) per entry. The routing wire is the
        // slab's ONLY home now: full-part decodes carry fp32 and no slab
        // (real tables rebuild writer-side slabs in the hydration prewarm;
        // this fixture declares no vector columns, so the prewarm is inert).
        let shape = |m: &ManifestSnapshot| {
            m.superfiles
                .iter()
                .map(|e| {
                    let clusters = &e.vector_summary["emb"].cells[0].clusters;
                    (
                        clusters.vectors_resident(),
                        clusters.admit_codes_built().is_some(),
                    )
                })
                .collect::<Vec<(bool, bool)>>()
        };

        let (_dir, storage) = local_storage();
        persist_summary_part_table(&storage, true).await;
        let knob_on = ManifestSnapshot::load(None, Arc::clone(&storage), Some(consumer_opts(true)))
            .await
            .expect("knob-on load");
        assert_eq!(
            shape(&knob_on),
            vec![(false, true), (false, true)],
            "knob-on consumer must hydrate stripped entries (slab riding) from the routing part"
        );
        let knob_off =
            ManifestSnapshot::load(None, Arc::clone(&storage), Some(consumer_opts(false)))
                .await
                .expect("knob-off load");
        assert_eq!(
            shape(&knob_off),
            vec![(true, false), (true, false)],
            "knob-off load must keep the full part's resident fp32 (slab rebuilt by prewarm \
             on real tables)"
        );

        // Pre-sibling manifest: knob-on falls back to the full part.
        let (_dir2, storage2) = local_storage();
        persist_summary_part_table(&storage2, false).await;
        let fallback =
            ManifestSnapshot::load(None, Arc::clone(&storage2), Some(consumer_opts(true)))
                .await
                .expect("fallback load");
        assert_eq!(
            shape(&fallback),
            vec![(true, false), (true, false)],
            "knob-on without a routing ref must fall back to the full part"
        );
    }

    /// [`rebuild_part_and_entry`] stamps the routing sibling on USER
    /// manifests: the entry's ref addresses exactly the sibling bytes
    /// returned for the commit PUT. Hidden (VectorCell) manifests write
    /// the part routing-shaped and skip the sibling entirely — the
    /// primary IS the slim form and fp32 lives in the slow-CAS section.
    #[tokio::test]
    async fn rebuild_part_and_entry_stamps_routing_sibling() {
        let (entry, encoded_part) =
            rebuild_part_and_entry(vec![], vec![make_summary_entry(10)], None, false);
        let routing = entry.routing.expect("sibling stamped");
        let routing_encoded = encoded_part
            .routing_encoded
            .as_ref()
            .expect("user part carries sibling bytes");
        assert_eq!(
            routing.content_hash,
            ContentHash::of(routing_encoded),
            "entry ref must address the returned sibling bytes"
        );
        assert_eq!(routing.uri, part_uri(&routing.content_hash));
        assert_eq!(entry.content_hash, ContentHash::of(&encoded_part.encoded));
        assert!(
            routing_encoded.len() < encoded_part.encoded.len(),
            "sibling must shed the fp32 payload"
        );

        let (hidden_entry, hidden_encoded) =
            rebuild_part_and_entry(vec![], vec![make_summary_entry(10)], None, true);
        assert!(
            hidden_entry.routing.is_none(),
            "hidden part must not stamp a sibling — its primary is routing-shaped"
        );
        assert!(
            hidden_encoded.routing_encoded.is_none(),
            "hidden part must not carry sibling bytes"
        );
        assert!(
            hidden_encoded.encoded.len() < encoded_part.encoded.len(),
            "hidden primary must shed the fp32 payload ({} vs {} bytes)",
            hidden_encoded.encoded.len(),
            encoded_part.encoded.len()
        );
    }

    /// Residency invariant: a refresh whose slow-state ref is unchanged
    /// (list-only churn — here a deleted-ids stamp) reuses the decoded
    /// entries — same `Arc`s, zero part loads, zero blob refetch.
    #[tokio::test]
    async fn refresh_with_unchanged_slow_ref_reuses_entries() {
        let opts = make_opts();
        let (_dir, storage) = local_storage();
        let entries = vec![
            make_superfile_entry(100, hash_bucket_0_pk()),
            make_superfile_entry(50, hash_bucket_0_pk()),
        ];
        let published = slow_vector_state::write_state(storage.as_ref(), &entries, None)
            .await
            .expect("write blob");
        let (blob_uri, blob_hash) = (published.uri, published.content_hash);
        persist_two_entry_table(&storage, Some((blob_uri, blob_hash))).await;

        let a = ManifestSnapshot::load(None, Arc::clone(&storage), Some(Arc::clone(&opts)))
            .await
            .expect("load A");
        // List-only churn: stamp deleted-ids (preserves the slow ref) and
        // publish it so the pointer advances past A.
        let (_, meta) = read_pointer(storage.as_ref())
            .await
            .expect("read pointer")
            .expect("pointer present");
        let etag = meta.etag.expect("localfs pointer etag");
        let stamped = a.with_deleted_user_ids(Vec::new());
        stamped
            .write(storage.as_ref(), Some(etag.as_str()), &[])
            .await
            .expect("stamp publish");

        let b = ManifestSnapshot::load(Some(Arc::clone(&a)), Arc::clone(&storage), None)
            .await
            .expect("refresh");
        assert_eq!(b.get_manifest_id(), a.get_manifest_id() + 1);
        assert!(b.slow_vector_state_blob().is_some(), "ref preserved");
        assert_eq!(b.superfiles.len(), a.superfiles.len());
        for (be, ae) in b.superfiles.iter().zip(a.superfiles.iter()) {
            assert!(
                Arc::ptr_eq(be, ae),
                "unchanged ref must reuse the SAME decoded entries — \
                 the centroid state never leaves memory on list-only churn"
            );
        }
        assert_eq!(
            n_parts_initialized(&b),
            0,
            "refresh with unchanged ref must not fetch parts"
        );
    }

    /// A list that carries a slow-state ref whose blob is missing or
    /// corrupt is a CORRUPT manifest: the load must raise
    /// [`ManifestLoadError::SlowStateHydration`] — never silently degrade
    /// to the part fan. (The old quiet fallback concealed hydration
    /// defects behind normal-looking, slower opens.)
    #[tokio::test]
    async fn load_with_corrupt_slow_ref_raises_hydration_error() {
        let opts = make_opts();
        let (_dir, storage) = local_storage();
        let bogus = (
            "slow-vector-state/state-missing.bin".to_string(),
            ContentHash([9u8; 32]),
        );
        persist_two_entry_table(&storage, Some(bogus)).await;

        let err = ManifestSnapshot::load(None, Arc::clone(&storage), Some(opts))
            .await
            .expect_err("corrupt slow-state ref must fail the load loudly");
        assert!(
            matches!(err, ManifestLoadError::SlowStateHydration(_)),
            "expected SlowStateHydration, got: {err:?}"
        );
    }

    #[tokio::test]
    async fn update_add_to_existing_partition_rewrites_part() {
        // Adding a new entry to the single existing part rewrites it in place.
        let opts = make_opts();

        let (_dir, storage) = local_storage();

        let old_superfile = make_superfile_entry(100, hash_bucket_0_pk());
        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![old_superfile.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 1,
                id_range: (0, 99),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);

        let parts = DashMap::new();
        parts.insert(
            pw.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![old_superfile],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // Add new entry to the SAME partition (not a new/cold partition)
        let new_entry = make_new_entry(50);
        let new_entries = vec![new_entry];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Should have 1 list entry (rewritten old one)
        assert_eq!(list_entries.len(), 1);
        // Should have 1 new part (the rewritten one)
        assert_eq!(parts.len(), 1);

        assert_eq!(list_entries[0].n_superfiles, 2);

        // Part should have combined superfiles
        assert_eq!(parts[0].part.superfiles.len(), 2);
        let total_docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 150);
    }

    #[tokio::test]
    async fn update_leaves_unchanged_parts_untouched() {
        // Start with three parts, two superfiles each, forming one table-level
        // lineage in list order: [part_0, part_1, part_2]. New entries append to
        // the LAST part (the latest), which here has room for one more superfile
        // (target = 3, so 2 + 1 = 3 stays within target → rewrite, no split). We
        // commit a single new superfile. After update ONLY the last part
        // changes; the two earlier parts must carry over byte-for-byte — same
        // part_id, uri, and content_hash — and must NOT be re-emitted into
        // `parts_to_write` (no re-encode, no PUT).
        const SUPERFILES_PER_PART: u64 = 2;
        const TARGET_SUPERFILES_PER_PART: u64 = 3;

        let (_dir, storage) = local_storage();

        // Attach storage so the manifests `update` derives also carry
        // a loader — the second (removal) phase loads carried-over parts
        // (part_0, part_1) back from storage.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = TARGET_SUPERFILES_PER_PART;
        let opts = Arc::new(base_opts.with_storage(storage.clone()));

        let pk_a = hash2_pk(0);
        let pk_b = hash2_pk(1);

        // Helper: build a 2-superfile part for a partition and persist it.
        async fn two_superfile_part(
            storage: &dyn StorageProvider,
            pk: &[u8],
            hint: u32,
            docs: [u64; 2],
        ) -> (ManifestPart, PartWriteResult) {
            let part = ManifestPart {
                format_version: part::FORMAT_VERSION.into(),
                part_id: PartId::new_v4(),
                superfiles: vec![
                    make_superfile_entry_hinted(docs[0], pk.to_vec(), hint),
                    make_superfile_entry_hinted(docs[1], pk.to_vec(), hint),
                ],
            };
            let pw = write_manifest_part(storage, &part)
                .await
                .expect("write part");
            (part, pw)
        }

        let (part_a_old, pw_a_old) =
            two_superfile_part(storage.as_ref(), &pk_a, 0, [100, 110]).await;
        let (_part_a_latest, pw_a_latest) =
            two_superfile_part(storage.as_ref(), &pk_a, 0, [120, 130]).await;
        let (part_b, pw_b) = two_superfile_part(storage.as_ref(), &pk_b, 1, [200, 210]).await;

        // Build a list entry mirroring a persisted part.
        let entry_for = |pw: &PartWriteResult| -> ManifestPartEntry {
            ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri.clone(),
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: SUPERFILES_PER_PART,
                id_range: (0, 0),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }
        };

        // List order: [part_0, part_1, part_2]. part_2 is the last
        // (rewrite candidate under option-B); part_0 and part_1 are
        // frozen earlier parts.
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 2,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                entry_for(&pw_a_old),
                entry_for(&pw_a_latest),
                entry_for(&pw_b),
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);

        // Only the latest (last) part is needed in-cache for the rewrite to
        // load + combine; the loader serves the rest from storage.
        let parts_map = DashMap::new();
        parts_map.insert(
            part_b.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_b.clone())))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: part_a_old
                    .superfiles
                    .iter()
                    .chain(part_b.superfiles.iter())
                    .cloned()
                    .collect(),
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // Commit one new superfile. Keep `new_entry` around — the second
        // phase below removes it again.
        let new_entry = make_new_entry_hinted(140, 0);
        let (new_manifest, parts_to_write) = old_manifest
            .update(from_ref(&new_entry), &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Three list entries remain (part_0 carried over, part_1 carried over,
        // part_2 rewritten in place), and only ONE part is re-emitted for
        // writing — the rewritten last part.
        assert_eq!(list_entries.len(), 3, "list entry count");
        assert_eq!(
            parts_to_write.len(),
            1,
            "only the rewritten last part should be re-emitted; \
             unchanged parts must not be re-encoded/PUT",
        );

        // Locate the carried-over entries by their original part_id and
        // assert they are byte-for-byte identical to what was persisted.
        let find = |part_id: PartId| {
            list_entries
                .iter()
                .find(|e| e.part_id == part_id)
                .unwrap_or_else(|| panic!("entry for part {part_id:?} missing after update"))
        };

        // part_0 carries over unchanged.
        let part0_after = find(pw_a_old.part_id);
        assert_eq!(part0_after.uri, pw_a_old.uri, "carried-over part_0 uri");
        assert_eq!(
            part0_after.content_hash, pw_a_old.content_hash,
            "carried-over part_0 content_hash",
        );
        assert_eq!(part0_after.n_superfiles, SUPERFILES_PER_PART);

        // part_1 carries over unchanged too.
        let part1_after = find(pw_a_latest.part_id);
        assert_eq!(part1_after.uri, pw_a_latest.uri, "carried-over part_1 uri");
        assert_eq!(
            part1_after.content_hash, pw_a_latest.content_hash,
            "carried-over part_1 content_hash",
        );
        assert_eq!(part1_after.n_superfiles, SUPERFILES_PER_PART);

        // The one re-emitted part is the rewritten last part: it now holds the
        // original two superfiles plus the new one.
        assert_eq!(
            parts_to_write[0].part.superfiles.len(),
            (SUPERFILES_PER_PART + 1) as usize,
            "rewritten last part should hold its 2 superfiles + the new one",
        );
        // And the original last part_id is gone from the list (it was
        // rewritten, not carried over).
        assert!(
            !list_entries.iter().any(|e| e.part_id == pw_b.part_id),
            "the rewritten last part is replaced, so its old part_id must not survive",
        );
        // The rewritten (last) entry is the one that is neither of the two
        // carried-over parts — it holds the combined superfiles.
        let rewritten_after = list_entries
            .iter()
            .find(|e| e.part_id != pw_a_old.part_id && e.part_id != pw_a_latest.part_id)
            .expect("rewritten last entry present after the add");
        assert_eq!(rewritten_after.n_superfiles, SUPERFILES_PER_PART + 1);

        // ---- Second phase: remove the superfile we just added --------
        //
        // The new superfile lives in the rewritten last part. Remove it. Only
        // that part should change. The two earlier parts never held the removed
        // superfile — both must carry over byte-for-byte.
        //
        // Capture the rewritten last part's identity (the part the removal will
        // legitimately rebuild).
        let rewritten_v1_part_id = rewritten_after.part_id;

        let (after_removal, removal_parts) = new_manifest
            .update(&[], from_ref(&new_entry))
            .await
            .expect("update removal");
        let entries_after = after_removal.get_all_list_entries();

        assert_eq!(entries_after.len(), 3, "list entry count after removal");

        // The part we removed from MUST change: its v1 part_id is gone.
        assert!(
            !entries_after
                .iter()
                .any(|e| e.part_id == rewritten_v1_part_id),
            "the part we removed a superfile from must be rebuilt (new part_id)",
        );

        // part_0 held none of the removed superfile — same part identity.
        let part0_after_removal = entries_after
            .iter()
            .find(|e| e.part_id == pw_a_old.part_id)
            .expect("part_0 must survive the removal unchanged");
        assert_eq!(
            part0_after_removal.uri, pw_a_old.uri,
            "part_0 uri after removal",
        );
        assert_eq!(
            part0_after_removal.content_hash, pw_a_old.content_hash,
            "part_0 content_hash after removal",
        );

        // part_1 held none of the removed superfile — same part identity.
        let part1_after_removal = entries_after
            .iter()
            .find(|e| e.part_id == pw_a_latest.part_id)
            .expect("part_1 must survive the removal unchanged");
        assert_eq!(
            part1_after_removal.uri, pw_a_latest.uri,
            "part_1 uri after removal",
        );
        assert_eq!(
            part1_after_removal.content_hash, pw_a_latest.content_hash,
            "part_1 content_hash after removal",
        );

        // Only the part that actually lost a superfile should be
        // re-emitted for writing.
        assert_eq!(
            removal_parts.len(),
            1,
            "only the part we removed from should be rewritten; unchanged parts \
             must not be re-encoded/PUT",
        );
    }

    #[tokio::test]
    async fn update_rewrite_partition_within_target() {
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 3;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf1 = make_superfile_entry(100, hash_bucket_0_pk());
        let sf2 = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf1.clone(), sf2.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);

        let parts = DashMap::new();
        parts.insert(
            pw.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf1, sf2],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // Add 1 new superfile to same partition (2 + 1 = 3, within target)
        let new_entry = make_new_entry(75);
        let new_entries = vec![new_entry];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Rewrite case: 1 list entry (old entry replaced), 1 new part
        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);

        assert_eq!(list_entries[0].n_superfiles, 3);

        // Part should have all 3 superfiles combined
        let part = &parts[0];
        assert_eq!(part.part.superfiles.len(), 3);
        // Verify combined doc count
        let total_docs: u64 = part.part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 325); // 100 + 150 + 75
    }

    #[tokio::test]
    async fn update_split_partition_exceeds_target() {
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 2;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf1 = make_superfile_entry(100, hash_bucket_0_pk());
        let sf2 = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf1.clone(), sf2.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);

        let parts = DashMap::new();
        parts.insert(
            pw.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf1, sf2],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // Add 2 new superfiles to same partition (2 + 2 = 4, exceeds target of 2)
        let new_entry1 = make_new_entry(75);
        let new_entry2 = make_new_entry(80);
        let new_entries = vec![new_entry1, new_entry2];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Split case: 2 list entries (old + fresh for split), 1 new part (fresh)
        assert_eq!(list_entries.len(), 2);
        assert_eq!(parts.len(), 1);

        // First entry is the carried-over existing part; the second is the
        // fresh split part holding the new superfiles.

        // First entry (old) should still have original superfiles
        assert_eq!(list_entries[0].n_superfiles, 2);

        // Second entry (fresh) should have the new superfiles
        assert_eq!(list_entries[1].n_superfiles, 2);

        // The one new part should have exactly the 2 new superfiles
        let part = &parts[0];
        assert_eq!(part.part.superfiles.len(), 2);
        let total_docs: u64 = part.part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 155); // 75 + 80
    }

    /// Hinted counterpart to [`make_superfile_entry`] — stamped, with a
    /// routing `partition_hint`.
    fn make_superfile_entry_hinted(docs: u64, pk: Vec<u8>, hint: u32) -> Arc<SuperfileEntry> {
        make_entry(docs, pk, Some(hint))
    }

    /// Hinted counterpart to [`make_new_entry`] — UNSTAMPED (empty
    /// partition_key), carrying a routing `partition_hint` for `update()` to
    /// derive the key from.
    fn make_new_entry_hinted(docs: u64, hint: u32) -> Arc<SuperfileEntry> {
        make_entry(docs, Vec::new(), Some(hint))
    }

    fn hash2_pk(bucket: u32) -> Vec<u8> {
        bucket.to_le_bytes().to_vec()
    }

    #[tokio::test]
    async fn update_split_partition_exceeds_size_threshold() {
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 10_000;
        // Any real encoded part is bigger than 1 byte, so the latest part is
        // always considered at-cap.
        base_opts.part_size_threshold_bytes = 1;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf1 = make_superfile_entry(100, hash_bucket_0_pk());
        let sf2 = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf1.clone(), sf2.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri.clone(),
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let frozen_part_id = pw.part_id;
        let frozen_hash = pw.content_hash;
        let loader = ManifestPartLoader::new(storage, &list);

        let parts = DashMap::new();
        parts.insert(
            pw.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf1, sf2],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // 2 + 1 = 3 superfiles — far under the 10_000 count target, so only
        // the size cap can force the split.
        let new_entries = vec![make_new_entry(75)];
        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        assert_eq!(
            list_entries.len(),
            2,
            "size-capped latest part must freeze; new entries go to a fresh part"
        );
        assert_eq!(parts.len(), 1, "only the fresh part is encoded + written");

        // The frozen part carries over byte-identical: same id, same hash —
        // no re-encode, no re-PUT.
        assert_eq!(list_entries[0].part_id, frozen_part_id);
        assert_eq!(list_entries[0].content_hash, frozen_hash);
        assert_eq!(list_entries[0].n_superfiles, 2);

        // The fresh part holds exactly the new superfile.
        assert_eq!(list_entries[1].n_superfiles, 1);
        assert_eq!(parts[0].part.superfiles.len(), 1);
        assert_eq!(parts[0].part.superfiles[0].n_docs, 75);
    }

    #[tokio::test]
    async fn update_older_entry_preserved_when_latest_rewritten() {
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 2;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf_old = make_superfile_entry(100, hash_bucket_0_pk());
        let sf_latest = make_superfile_entry(150, hash_bucket_0_pk());

        let part_old = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_old.clone()],
        };
        let pw_old = write_manifest_part(storage.as_ref(), &part_old)
            .await
            .expect("write part_old");

        let part_latest = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_latest.clone()],
        };
        let pw_latest = write_manifest_part(storage.as_ref(), &part_latest)
            .await
            .expect("write part_latest");

        // Old manifest with TWO entries for same partition (result of prior split)
        // Second one is the "latest" for that partition
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_old.part_id,
                    uri: pw_old.uri.clone(),
                    content_hash: pw_old.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_old.size_bytes_compressed,
                    size_bytes_uncompressed: pw_old.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 99),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_latest.part_id,
                    uri: pw_latest.uri,
                    content_hash: pw_latest.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_latest.size_bytes_compressed,
                    size_bytes_uncompressed: pw_latest.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 149),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);

        let parts = DashMap::new();
        parts.insert(
            part_latest.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_latest)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_old, sf_latest],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // Add one new entry for the partition
        let new_entries = vec![make_new_entry(75)];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Expect: old entry (preserved) + latest entry (rewritten) = 2 list entries
        // Expect: 1 new part (latest rewrite)
        assert_eq!(list_entries.len(), 2);
        assert_eq!(parts.len(), 1);

        // First entry should carry over the old one unchanged
        assert_eq!(list_entries[0].n_superfiles, 1);
        // URI should be exactly the same as the original written part
        assert_eq!(list_entries[0].uri, pw_old.uri);

        // Second entry should be the rewritten latest (1 + 1 = 2 superfiles)
        assert_eq!(list_entries[1].n_superfiles, 2);

        // New part should have the combined latest + new
        assert_eq!(parts[0].part.superfiles.len(), 2);
        let total_docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 225); // 150 + 75
    }

    // ---- cross-partition tests --------------------------------------------

    #[tokio::test]
    async fn update_two_partitions_both_touched() {
        // Two existing parts hold superfiles tagged with different partition
        // hints. New entries carrying both hints are added in one commit. Parts
        // are a single table-level lineage now, so the new entries all append to
        // the LAST existing part (the latest); the earlier part carries over
        // unchanged. Each superfile keeps its own partition_hint/partition_key.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 3;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf_a = make_superfile_entry_hinted(100, hash2_pk(0), 0);
        let part_a = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a.clone()],
        };
        let pw_a = write_manifest_part(storage.as_ref(), &part_a)
            .await
            .expect("write part_a");

        let sf_b = make_superfile_entry_hinted(200, hash2_pk(1), 1);
        let part_b = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_b.clone()],
        };
        let pw_b = write_manifest_part(storage.as_ref(), &part_b)
            .await
            .expect("write part_b");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 2,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_a.part_id,
                    uri: pw_a.uri,
                    content_hash: pw_a.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 99),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_b.part_id,
                    uri: pw_b.uri,
                    content_hash: pw_b.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_b.size_bytes_compressed,
                    size_bytes_uncompressed: pw_b.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 199),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            part_a.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a)))),
        );
        parts_map.insert(
            part_b.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_b)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_a, sf_b],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let new_entries = vec![make_new_entry_hinted(50, 0), make_new_entry_hinted(80, 1)];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Single lineage: the earlier part carries over, the latest part is
        // rewritten with both new entries appended. 2 list entries, 1 new part.
        assert_eq!(list_entries.len(), 2);
        assert_eq!(parts.len(), 1);

        // [0] The earlier part carries over unchanged — original part_id
        // preserved, still its single original superfile.
        assert_eq!(list_entries[0].part_id, pw_a.part_id);
        assert_eq!(list_entries[0].n_superfiles, 1);
        assert_eq!(list_entries[0].content_hash, pw_a.content_hash);

        // [1] The latest part is rewritten: its 1 existing superfile + both new
        // ones = 3 superfiles.
        assert_eq!(list_entries[1].n_superfiles, 3);
        assert_eq!(parts[0].part.superfiles.len(), 3);
        let total_docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 330); // 200 (existing B) + 50 + 80

        // Each new superfile kept its own partition_hint (the routing tag is
        // independent of the part's table-level grouping key).
        let hints: Vec<_> = parts[0]
            .part
            .superfiles
            .iter()
            .map(|s| s.partition_hint)
            .collect();
        assert!(hints.contains(&Some(0)), "hint-0 new entry preserved");
        assert!(hints.contains(&Some(1)), "hint-1 new entry preserved");
    }

    #[tokio::test]
    async fn update_two_partitions_one_touched_exact_carry_over() {
        // One new entry is committed. Parts are a single table-level lineage, so
        // it appends to the LAST existing part (the latest), which is rewritten;
        // the earlier part carries over with the exact URI and content_hash that
        // were written — no re-encode, no PUT.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 3;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf_a = make_superfile_entry_hinted(100, hash2_pk(0), 0);
        let part_a = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a.clone()],
        };
        let pw_a = write_manifest_part(storage.as_ref(), &part_a)
            .await
            .expect("write part_a");

        let sf_b = make_superfile_entry_hinted(200, hash2_pk(1), 1);
        let part_b = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_b.clone()],
        };
        let pw_b = write_manifest_part(storage.as_ref(), &part_b)
            .await
            .expect("write part_b");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 2,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_a.part_id,
                    uri: pw_a.uri.clone(),
                    content_hash: pw_a.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 99),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_b.part_id,
                    uri: pw_b.uri,
                    content_hash: pw_b.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_b.size_bytes_compressed,
                    size_bytes_uncompressed: pw_b.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 199),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            part_a.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a)))),
        );
        parts_map.insert(
            part_b.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_b)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_a, sf_b],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // Only touch partition A
        let new_entries = vec![make_new_entry_hinted(50, 0)];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // 2 list entries (earlier part carried over, latest rewritten), 1 new part
        assert_eq!(list_entries.len(), 2);
        assert_eq!(parts.len(), 1);

        // [0] Earlier part: exact carry-over — part_id and content_hash unchanged.
        assert_eq!(list_entries[0].part_id, pw_a.part_id);
        assert_eq!(list_entries[0].n_superfiles, 1);
        assert_eq!(list_entries[0].content_hash, pw_a.content_hash);

        // [1] Latest part: rewritten with its existing superfile + the new one =
        // 2 superfiles, 250 docs.
        assert_eq!(list_entries[1].n_superfiles, 2);
        assert_eq!(parts[0].part.superfiles.len(), 2);
        let docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(docs, 250); // 200 (existing B) + 50 (new)
    }

    #[tokio::test]
    async fn update_two_partitions_each_with_prior_split() {
        // Four existing parts from prior splits, in one table-level lineage:
        // [p0, p1, p2, p3]. Two new entries (different partition hints) are
        // committed. They append to the LAST part (p3, the latest); p3 already
        // holds 1 superfile so 1 + 2 = 3 exceeds the target of 2 — a split. The
        // split keeps p3 as-is and emits a fresh part holding just the 2 new
        // entries. p0..p2 carry over unchanged. Each superfile keeps its own
        // partition_hint.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 2;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        // Partition A: two parts
        let sf_a_old = make_superfile_entry_hinted(100, hash2_pk(0), 0);
        let part_a_old = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_old.clone()],
        };
        let pw_a_old = write_manifest_part(storage.as_ref(), &part_a_old)
            .await
            .expect("write part_a_old");

        let sf_a_latest = make_superfile_entry_hinted(150, hash2_pk(0), 0);
        let part_a_latest = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_latest.clone()],
        };
        let pw_a_latest = write_manifest_part(storage.as_ref(), &part_a_latest)
            .await
            .expect("write part_a_latest");

        // Partition B: two parts
        let sf_b_old = make_superfile_entry_hinted(200, hash2_pk(1), 1);
        let part_b_old = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_b_old.clone()],
        };
        let pw_b_old = write_manifest_part(storage.as_ref(), &part_b_old)
            .await
            .expect("write part_b_old");

        let sf_b_latest = make_superfile_entry_hinted(250, hash2_pk(1), 1);
        let part_b_latest = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_b_latest.clone()],
        };
        let pw_b_latest = write_manifest_part(storage.as_ref(), &part_b_latest)
            .await
            .expect("write part_b_latest");

        // List order: [a_old, a_latest, b_old, b_latest]
        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 2,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_a_old.part_id,
                    uri: pw_a_old.uri.clone(),
                    content_hash: pw_a_old.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a_old.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a_old.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 99),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_a_latest.part_id,
                    uri: pw_a_latest.uri.clone(),
                    content_hash: pw_a_latest.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a_latest.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a_latest.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 149),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_b_old.part_id,
                    uri: pw_b_old.uri.clone(),
                    content_hash: pw_b_old.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_b_old.size_bytes_compressed,
                    size_bytes_uncompressed: pw_b_old.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 199),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_b_latest.part_id,
                    uri: pw_b_latest.uri.clone(),
                    content_hash: pw_b_latest.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_b_latest.size_bytes_compressed,
                    size_bytes_uncompressed: pw_b_latest.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 249),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            part_a_latest.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a_latest)))),
        );
        parts_map.insert(
            part_b_latest.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_b_latest)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_a_old, sf_a_latest, sf_b_old, sf_b_latest],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let new_entries = vec![make_new_entry_hinted(75, 0), make_new_entry_hinted(90, 1)];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // 5 list entries: the 4 existing parts all carry over, plus 1 fresh
        // split part holding the 2 new entries.
        assert_eq!(list_entries.len(), 5);
        // 1 new part: the fresh split.
        assert_eq!(parts.len(), 1);

        // [0..=3] The four existing parts carry over unchanged — original
        // part_ids preserved, one superfile each.
        assert_eq!(list_entries[0].part_id, pw_a_old.part_id);
        assert_eq!(list_entries[0].uri, pw_a_old.uri);
        assert_eq!(list_entries[0].content_hash, pw_a_old.content_hash);

        assert_eq!(list_entries[1].part_id, pw_a_latest.part_id);

        assert_eq!(list_entries[2].part_id, pw_b_old.part_id);
        assert_eq!(list_entries[2].uri, pw_b_old.uri);
        assert_eq!(list_entries[2].content_hash, pw_b_old.content_hash);

        assert_eq!(list_entries[3].part_id, pw_b_latest.part_id);

        for e in &list_entries[0..4] {
            assert_eq!(e.n_superfiles, 1);
        }

        // [4] Fresh split part: the 2 new entries. 165 docs (75 + 90).
        assert_eq!(list_entries[4].n_superfiles, 2);
        assert_eq!(parts[0].part.superfiles.len(), 2);
        let docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(docs, 165); // 75 (hint 0) + 90 (hint 1)

        // The new superfiles kept their own partition hints.
        let hints: Vec<_> = parts[0]
            .part
            .superfiles
            .iter()
            .map(|s| s.partition_hint)
            .collect();
        assert!(hints.contains(&Some(0)), "hint-0 new entry preserved");
        assert!(hints.contains(&Some(1)), "hint-1 new entry preserved");
    }

    #[tokio::test]
    async fn update_multiple_partitions_land_in_one_lineage() {
        // A single commit of several new superfiles carrying DIFFERENT
        // partition hints (well under the target) produces ONE table-level part
        // holding ALL of them. Each superfile keeps its own partition_hint —
        // the routing tag is independent of the part's table-level grouping.
        // Under the default single-bucket Hash strategy the commit-time
        // partition_key stamped on every entry is bucket 0, regardless of hint.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 8;
        let opts = Arc::new(base_opts);

        let old_manifest = empty_manifest(&opts);

        let hints = [0u32, 1, 2, 3];
        let new_entries: Vec<_> = hints
            .iter()
            .enumerate()
            .map(|(i, &h)| make_new_entry_hinted(100 + i as u64, h))
            .collect();

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, &[])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // One part holding all four.
        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);
        assert_eq!(list_entries[0].n_superfiles, hints.len() as u64);
        assert_eq!(parts[0].part.superfiles.len(), hints.len());

        // Every original superfile is present, each kept its own
        // partition_hint, and each carries the commit-time partition_key
        // stamped by `update` — bucket 0 under the single-bucket Hash default.
        for (&h, expected) in hints.iter().zip(new_entries.iter()) {
            let landed = parts[0]
                .part
                .superfiles
                .iter()
                .find(|s| s.superfile_id == expected.superfile_id)
                .unwrap_or_else(|| panic!("superfile with hint {h} landed in the part"));
            assert_eq!(landed.partition_hint, Some(h), "partition_hint preserved");
            assert_eq!(
                landed.partition_key,
                hash2_pk(0),
                "single-bucket Hash stamps bucket 0 on every entry"
            );
        }
    }

    // ---- removal tests ---------------------------------------------------

    #[tokio::test]
    async fn update_remove_one_superfile_from_partition() {
        // Partition has 2 superfiles; remove one. Verifies the part is
        // rewritten containing only the superfile that was not removed.
        let opts = make_opts();
        let (_dir, storage) = local_storage();

        let sf_keep = make_superfile_entry(100, hash_bucket_0_pk());
        let sf_remove = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_keep.clone(), sf_remove.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            existing_part.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_keep.clone(), sf_remove.clone()],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let (new_manifest, parts) = old_manifest
            .update(&[], from_ref(&sf_remove))
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Part rewritten with 1 superfile; no cold entries.
        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);
        assert_eq!(list_entries[0].n_superfiles, 1);
        assert_eq!(parts[0].part.superfiles.len(), 1);
        assert_eq!(
            parts[0].part.superfiles[0].superfile_id,
            sf_keep.superfile_id
        );
        let total_docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 100);
    }

    #[tokio::test]
    async fn update_add_and_remove_in_same_partition() {
        // One new superfile is added while one existing superfile is removed
        // in the same partition. The resulting part should contain the
        // surviving existing superfile plus the new one — not the removed one.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 3;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        let sf_keep = make_superfile_entry(100, hash_bucket_0_pk());
        let sf_remove = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_keep.clone(), sf_remove.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            existing_part.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_keep.clone(), sf_remove.clone()],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let sf_new = make_new_entry(75);
        let new_entries = vec![sf_new.clone()];

        let (new_manifest, parts) = old_manifest
            .update(&new_entries, from_ref(&sf_remove))
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Net result: 1 list entry, 1 part — sf_keep + sf_new, sf_remove absent
        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);
        assert_eq!(list_entries[0].n_superfiles, 2);
        assert_eq!(parts[0].part.superfiles.len(), 2);

        let ids: Vec<_> = parts[0]
            .part
            .superfiles
            .iter()
            .map(|s| s.superfile_id)
            .collect();
        assert!(ids.contains(&sf_keep.superfile_id));
        assert!(ids.contains(&sf_new.superfile_id));
        assert!(!ids.contains(&sf_remove.superfile_id));

        let total_docs: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(total_docs, 175); // 100 + 75
    }

    #[tokio::test]
    async fn update_remove_from_one_partition_other_carried_over_exactly() {
        // Two parts. The removed superfile lives only in the first part. Removals
        // are checked against every part: the first part matches and is
        // rewritten; the second holds no matching id and carries over with the
        // exact URI and content_hash — no re-encode, no PUT.
        let opts = make_opts();
        let (_dir, storage) = local_storage();

        let sf_a_keep = make_superfile_entry_hinted(100, hash2_pk(0), 0);
        let sf_a_remove = make_superfile_entry_hinted(150, hash2_pk(0), 0);
        let part_a = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_keep.clone(), sf_a_remove.clone()],
        };
        let pw_a = write_manifest_part(storage.as_ref(), &part_a)
            .await
            .expect("write part_a");

        let sf_b = make_superfile_entry_hinted(200, hash2_pk(1), 1);
        let part_b = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_b.clone()],
        };
        let pw_b = write_manifest_part(storage.as_ref(), &part_b)
            .await
            .expect("write part_b");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 2,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_a.part_id,
                    uri: pw_a.uri,
                    content_hash: pw_a.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a.size_bytes_uncompressed,
                    n_superfiles: 2,
                    id_range: (0, 149),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_b.part_id,
                    uri: pw_b.uri.clone(),
                    content_hash: pw_b.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_b.size_bytes_compressed,
                    size_bytes_uncompressed: pw_b.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 199),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            part_a.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a)))),
        );
        parts_map.insert(
            part_b.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_b)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf_a_keep.clone(), sf_a_remove.clone(), sf_b.clone()],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let (new_manifest, parts) = old_manifest
            .update(&[], from_ref(&sf_a_remove))
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // 2 list entries, 1 new part (only the first part was rewritten)
        assert_eq!(list_entries.len(), 2);
        assert_eq!(parts.len(), 1);

        // First part: rewritten with 1 surviving superfile.
        assert_eq!(list_entries[0].n_superfiles, 1);
        assert_eq!(parts[0].part.superfiles.len(), 1);
        assert_eq!(
            parts[0].part.superfiles[0].superfile_id,
            sf_a_keep.superfile_id
        );
        let docs_a: u64 = parts[0].part.superfiles.iter().map(|s| s.n_docs).sum();
        assert_eq!(docs_a, 100);

        // Second part: exact carry-over — URI and content_hash unchanged.
        assert_eq!(list_entries[1].n_superfiles, 1);
        assert_eq!(list_entries[1].uri, pw_b.uri);
        assert_eq!(list_entries[1].content_hash, pw_b.content_hash);
    }

    #[tokio::test]
    async fn update_remove_from_latest_part_in_split_partition() {
        // Two parts from a prior split: part_a_old (1 sf) and part_a_latest
        // (2 sfs). We remove sf_a_latest_remove, which lives in the SECOND
        // (latest) part. The removal set is checked against every part:
        // part_a_old holds no matching id and carries over unchanged, while
        // part_a_latest matches and is rewritten with only its surviving
        // superfile.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 2;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        // part_a_old: frozen entry from a prior split
        let sf_a_old = make_superfile_entry(100, hash_bucket_0_pk());
        let part_a_old = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_old.clone()],
        };
        let pw_a_old = write_manifest_part(storage.as_ref(), &part_a_old)
            .await
            .expect("write part_a_old");

        // part_a_latest: current mutable entry; contains the sf to remove
        let sf_a_latest_keep = make_superfile_entry(150, hash_bucket_0_pk());
        let sf_a_latest_remove = make_superfile_entry(200, hash_bucket_0_pk());
        let part_a_latest = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_latest_keep.clone(), sf_a_latest_remove.clone()],
        };
        let pw_a_latest = write_manifest_part(storage.as_ref(), &part_a_latest)
            .await
            .expect("write part_a_latest");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_a_old.part_id,
                    uri: pw_a_old.uri.clone(),
                    content_hash: pw_a_old.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a_old.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a_old.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 99),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_a_latest.part_id,
                    uri: pw_a_latest.uri.clone(),
                    content_hash: pw_a_latest.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a_latest.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a_latest.size_bytes_uncompressed,
                    n_superfiles: 2,
                    id_range: (0, 199),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            part_a_old.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a_old)))),
        );
        parts_map.insert(
            part_a_latest.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a_latest)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![
                    sf_a_old.clone(),
                    sf_a_latest_keep.clone(),
                    sf_a_latest_remove.clone(),
                ],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let (new_manifest, parts_to_write) = old_manifest
            .update(&[], from_ref(&sf_a_latest_remove))
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        assert_eq!(list_entries.len(), 2);
        // Only the part that actually held the removed superfile is rewritten;
        // the other carries over untouched.
        assert_eq!(parts_to_write.len(), 1);

        // [0] part_a_old carried over. [1] part_a_latest rewritten.

        // sf_a_old survives (in one of the output parts)
        // sf_a_latest_keep survives (in one of the output parts)
        // sf_a_latest_remove is absent from every output part
        let all_ids: Vec<_> = parts_to_write
            .iter()
            .flat_map(|ep| ep.part.superfiles.iter())
            .map(|s| s.superfile_id)
            .collect();
        assert!(
            all_ids.contains(&sf_a_latest_keep.superfile_id),
            "sf_a_latest_keep must survive"
        );
        assert!(
            !all_ids.contains(&sf_a_latest_remove.superfile_id),
            "sf_a_latest_remove must be absent"
        );

        // Each rewritten part has exactly 1 superfile
        assert_eq!(list_entries[0].n_superfiles, 1);
        assert_eq!(list_entries[1].n_superfiles, 1);
    }

    #[tokio::test]
    async fn update_remove_all_superfiles_empties_partition() {
        // All superfiles in a partition are removed. Documents the current
        // behavior: the list entry survives with n_superfiles=0 and the
        // part has no superfiles (empty partition).
        let opts = make_opts();
        let (_dir, storage) = local_storage();

        let sf1 = make_superfile_entry(100, hash_bucket_0_pk());
        let sf2 = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf1.clone(), sf2.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            existing_part.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf1.clone(), sf2.clone()],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let (new_manifest, parts) = old_manifest
            .update(&[], &[sf1.clone(), sf2.clone()])
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        // Both superfiles removed: list entry remains with n_superfiles=0.
        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts.len(), 1);
        assert_eq!(list_entries[0].n_superfiles, 0);
        assert_eq!(parts[0].part.superfiles.len(), 0);
    }

    #[tokio::test]
    async fn update_remove_nonexistent_superfile_id_is_noop() {
        // entries_to_remove contains a superfile_id that is not present in any
        // part. The filter matches nothing and both original superfiles survive.
        // The part is still rewritten (the removal loop doesn't skip parts where
        // no removal matched), so n_superfiles stays at 2.
        let opts = make_opts();
        let (_dir, storage) = local_storage();

        let sf1 = make_superfile_entry(100, hash_bucket_0_pk());
        let sf2 = make_superfile_entry(150, hash_bucket_0_pk());

        let existing_part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf1.clone(), sf2.clone()],
        };
        let pw = write_manifest_part(storage.as_ref(), &existing_part)
            .await
            .expect("write part");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![ManifestPartEntry {
                part_id: pw.part_id,
                uri: pw.uri,
                content_hash: pw.content_hash,
                routing: None,
                size_bytes_compressed: pw.size_bytes_compressed,
                size_bytes_uncompressed: pw.size_bytes_uncompressed,
                n_superfiles: 2,
                id_range: (0, 149),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            }],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            existing_part.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(existing_part)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![sf1.clone(), sf2.clone()],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        // sf_ghost was never added to any part; its superfile_id won't match anything
        let sf_ghost = make_superfile_entry(50, hash_bucket_0_pk());

        let (new_manifest, parts_to_write) = old_manifest
            .update(&[], from_ref(&sf_ghost))
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        assert_eq!(list_entries.len(), 1);
        assert_eq!(parts_to_write.len(), 0);
        assert_eq!(list_entries[0].n_superfiles, 2);
    }

    #[tokio::test]
    async fn update_remove_from_older_frozen_part_in_split_partition() {
        // Two parts from a prior split: part_a_old (2 sfs: sf_a_old_keep +
        // sf_a_old_remove) and part_a_latest (1 sf). We remove sf_a_old_remove,
        // which lives in the FIRST (older) part. The removal set is checked
        // against every part: part_a_old matches and is rewritten without the
        // removed superfile; part_a_latest holds no matching id and carries over
        // unchanged. sf_a_old_keep and sf_a_latest survive.
        let mut base_opts =
            SupertableOptions::new(simple_schema(), vec![], vec![], None).expect("valid options");
        base_opts.target_superfiles_per_part = 2;
        let opts = Arc::new(base_opts);

        let (_dir, storage) = local_storage();

        // part_a_old: frozen entry — contains the sf to remove
        let sf_a_old_keep = make_superfile_entry(100, hash_bucket_0_pk());
        let sf_a_old_remove = make_superfile_entry(150, hash_bucket_0_pk());
        let part_a_old = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_old_keep.clone(), sf_a_old_remove.clone()],
        };
        let pw_a_old = write_manifest_part(storage.as_ref(), &part_a_old)
            .await
            .expect("write part_a_old");

        // part_a_latest: mutable entry — does not contain the sf to remove
        let sf_a_latest = make_superfile_entry(200, hash_bucket_0_pk());
        let part_a_latest = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![sf_a_latest.clone()],
        };
        let pw_a_latest = write_manifest_part(storage.as_ref(), &part_a_latest)
            .await
            .expect("write part_a_latest");

        let list = Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 0,
            options_hash: ContentHash([0u8; 32]),
            schema: vec![],
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts: vec![
                ManifestPartEntry {
                    part_id: pw_a_old.part_id,
                    uri: pw_a_old.uri,
                    content_hash: pw_a_old.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a_old.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a_old.size_bytes_uncompressed,
                    n_superfiles: 2,
                    id_range: (0, 149),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
                ManifestPartEntry {
                    part_id: pw_a_latest.part_id,
                    uri: pw_a_latest.uri,
                    content_hash: pw_a_latest.content_hash,
                    routing: None,
                    size_bytes_compressed: pw_a_latest.size_bytes_compressed,
                    size_bytes_uncompressed: pw_a_latest.size_bytes_uncompressed,
                    n_superfiles: 1,
                    id_range: (0, 199),
                    scalar_stats_agg: Default::default(),
                    fts_summary_agg: Default::default(),
                },
            ],
        };
        let loader = ManifestPartLoader::new(storage, &list);
        let parts_map = DashMap::new();
        parts_map.insert(
            part_a_old.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a_old)))),
        );
        parts_map.insert(
            part_a_latest.part_id,
            Arc::new(OnceCell::new_with(Some(Arc::new(part_a_latest)))),
        );
        let old_manifest = Arc::new(ManifestSnapshot {
            superfile_list: SuperfileList {
                manifest_id: 0,
                options: opts.clone(),
                superfiles: vec![
                    sf_a_old_keep.clone(),
                    sf_a_old_remove.clone(),
                    sf_a_latest.clone(),
                ],
                vector_index_storage_prefix: None,
            },
            list: Some(list),
            parts: parts_map,
            loader: Some(Arc::new(loader)),
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        });

        let (new_manifest, parts_to_write) = old_manifest
            .update(&[], from_ref(&sf_a_old_remove))
            .await
            .expect("update");
        let list_entries = new_manifest.get_all_list_entries();

        assert_eq!(list_entries.len(), 2);
        // Only the part that held the removed superfile is rewritten; the other
        // carries over untouched.
        assert_eq!(parts_to_write.len(), 1);

        // [0] part_a_old rewritten. [1] part_a_latest carried over.

        // sf_a_old_keep and sf_a_latest survive; sf_a_old_remove is absent
        let all_ids: Vec<_> = parts_to_write
            .iter()
            .flat_map(|ep| ep.part.superfiles.iter())
            .map(|s| s.superfile_id)
            .collect();
        assert!(
            all_ids.contains(&sf_a_old_keep.superfile_id),
            "sf_a_old_keep must survive"
        );
        assert!(
            !all_ids.contains(&sf_a_old_remove.superfile_id),
            "sf_a_old_remove must be absent"
        );

        // Old part now has 1 sf (sf_a_old_remove was removed)
        assert_eq!(list_entries[0].n_superfiles, 1);
        // Latest part still has 1 sf (removal did not touch it)
        assert_eq!(list_entries[1].n_superfiles, 1);
    }

    /// Build a single-part `Manifest` carrying `n_parts` placeholder
    /// entries — enough to exercise the list-aware `ManifestSnapshot` accessors
    /// without attaching storage.
    fn list_with_parts(n_parts: usize) -> list::Manifest {
        use list::{Manifest, ManifestPartEntry, PartitionStrategy};
        let parts = (0..n_parts)
            .map(|i| ManifestPartEntry {
                part_id: part::PartId(Uuid::from_u128(i as u128 + 1)),
                uri: format!("manifests/part-{i}"),
                n_superfiles: 0,
                size_bytes_compressed: 0,
                size_bytes_uncompressed: 0,
                content_hash: part::ContentHash([0u8; 32]),
                routing: None,
                id_range: (0, 0),
                scalar_stats_agg: Default::default(),
                fts_summary_agg: Default::default(),
            })
            .collect();
        Manifest {
            drained_ranges: Default::default(),
            global_vector_index: None,
            tombstone_seqs: Default::default(),
            format_version: list::FORMAT_VERSION.into(),
            manifest_id: 1,
            options_hash: part::ContentHash([0u8; 32]),
            schema: Vec::new(),
            id_column: "_id".into(),
            fts_columns: vec![],
            vector_columns: vec![],
            partition_strategy: PartitionStrategy::Hash {
                column: "_id".into(),
                n_buckets: 1,
            },
            vector_index_storage_prefix: None,
            deleted_user_ids_inline: None,
            slow_vector_state_uri: None,
            slow_vector_state_content_hash: None,
            slow_vector_state_centroids: None,
            parts,
        }
    }

    fn manifest_with_list(list: list::Manifest) -> ManifestSnapshot {
        ManifestSnapshot {
            superfile_list: SuperfileList::empty(opts()),
            list: Some(list),
            parts: DashMap::new(),
            loader: None,
            stamped_partition_strategy: None,
            stamped_global_vector_index: None,
            stamped_drained_ranges: None,
        }
    }

    /// `get_num_parts` / `get_all_list_entries` read straight off the
    /// attached `Manifest` (the Some-arm of both accessors).
    #[test]
    fn list_accessors_read_from_attached_list() {
        let m = manifest_with_list(list_with_parts(3));
        assert_eq!(m.get_num_parts(), 3);
        assert_eq!(m.get_all_list_entries().len(), 3);
        assert_eq!(m.get_num_parts_loaded(), 0, "nothing eagerly loaded");
        assert!(!m.is_in_process_only(), "a list is attached");

        // No-list manifest takes the None-arms.
        let empty = ManifestSnapshot::empty(opts());
        assert_eq!(empty.get_num_parts(), 0);
        assert!(empty.get_all_list_entries().is_empty());
        assert!(empty.is_in_process_only());
    }

    #[test]
    fn complete_flat_superfiles_rejects_partial_part_view() {
        let mut list = list_with_parts(1);
        list.parts[0].n_superfiles = 1;
        let mut manifest = manifest_with_list(list);
        assert!(
            manifest.complete_flat_superfiles().is_none(),
            "empty resident view cannot represent one listed superfile"
        );

        manifest
            .superfile_list
            .superfiles
            .push(seg_entry(Uuid::new_v4(), 4));
        let complete = manifest
            .complete_flat_superfiles()
            .expect("resident count now matches list");
        assert_eq!(complete.len(), 1);
    }

    /// `get_cached_part_by_id` / `get_cached_part_by_list_idx` return
    /// `None` before any part is fetched into the per-part cache; the
    /// list-index variant resolves the index to a `PartId` first.
    #[test]
    fn cached_part_lookups_miss_before_load() {
        let m = manifest_with_list(list_with_parts(2));
        let known_id = part::PartId(Uuid::from_u128(1));
        assert!(m.get_cached_part_by_id(&known_id).is_none());
        assert!(m.get_cached_part_by_list_idx(0).is_none());
        assert!(m.get_cached_part_by_list_idx(1).is_none());

        // A manifest with no list has no parts to resolve by index.
        let empty = ManifestSnapshot::empty(opts());
        assert!(empty.get_cached_part_by_list_idx(0).is_none());
    }

    /// `ManifestSnapshot::new` with no storage/list takes the in-process-only
    /// constructor branch (loader + list both `None`).
    #[test]
    fn manifest_new_without_storage_is_in_process_only() {
        let m = ManifestSnapshot::new(7, opts(), vec![seg_entry(Uuid::new_v4(), 4)], None, None);
        assert_eq!(m.get_manifest_id(), 7);
        assert!(m.is_in_process_only());
        assert_eq!(m.get_num_parts(), 0);
        assert_eq!(m.superfiles.len(), 1);
    }

    /// `ClusterCentroids::from_fp32` clamps non-finite components to zero.
    #[test]
    fn from_fp32_handles_non_finite_components() {
        let centroids = [f32::INFINITY, f32::NEG_INFINITY, 0.0, 1.0];
        let cc = ClusterCentroids::from_fp32(1, 4, &centroids, vec![1]);
        let out = cc.centroid(0);
        assert!(out.iter().all(|v| v.is_finite()));
        assert_eq!(out[0], 0.0);
        assert_eq!(out[1], 0.0);
        assert_eq!(out[2], 0.0);
        assert_eq!(out[3], 1.0);
    }

    /// `decode_part_off_thread` decodes valid part bytes on the blocking pool
    /// back to a part equal to the original, and surfaces a typed error (not a
    /// panic / task-join failure) on garbage input.
    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn decode_part_off_thread_roundtrips_and_rejects_garbage() {
        let id = Uuid::new_v4();
        let seg = Arc::new(SuperfileEntry {
            birth_version: 0,
            superfile_id: id,
            uri: SuperfileUri(id),
            n_docs: 3,
            id_min: -5,
            id_max: 7,
            scalar_stats: HashMap::new(),
            fts_summary: HashMap::new(),
            vector_summary: HashMap::new(),
            partition_key: Vec::new(),
            partition_hint: None,
            vector_layout: VectorLayout::Ivf,
            subsection_offsets: None,
        });
        let part = ManifestPart {
            format_version: part::FORMAT_VERSION.into(),
            part_id: PartId::new_v4(),
            superfiles: vec![seg],
        };
        let bytes = part::encode(&part);

        let decoded = decode_part_off_thread(Bytes::from(bytes))
            .await
            .expect("valid part decodes off-thread");
        assert_eq!(decoded.part_id, part.part_id, "part_id round-trips");
        assert_eq!(decoded.superfiles.len(), 1);
        assert_eq!(decoded.superfiles[0].superfile_id, id);
        assert_eq!(decoded.superfiles[0].id_min, -5);
        assert_eq!(decoded.superfiles[0].id_max, 7);

        // Garbage bytes surface a typed error, not a panic.
        let err = decode_part_off_thread(Bytes::from_static(b"not-a-valid-part-blob"))
            .await
            .expect_err("garbage bytes must fail to decode");
        assert!(
            matches!(err, ManifestLoadError::Parse(_)),
            "expected a parse error, got {err:?}"
        );
    }
}