inkferro_core/layout/

taffy_engine.rs

//! `TaffyEngine` — the Taffy 0.10 backend for `LayoutEngine`.
//!
//! See `mod.rs` for measure-seam and rounding rationale.
//!
//! ## Id mapping
//! The dom arena owns u32 ids allocated by the JS reconciler.  `TaffyEngine`
//! maintains a `HashMap<u32, taffy::NodeId>` (dom id → taffy id).  Each taffy
//! node carries the corresponding dom id as its `NodeContext` (`TaffyTree<u32>`),
//! so the measure closure receives it directly as a parameter — no reverse map
//! needed, no per-calculate clone.

use std::collections::HashMap;

use taffy::{
    NodeId, TaffyTree, TraversePartialTree,
    geometry::{Point, Rect as TaffyRect, Size},
    style::{
        AlignContent, AlignItems, AlignSelf, AvailableSpace, Dimension, Display as TaffyDisplay,
        FlexDirection, FlexWrap as TaffyFlexWrap, JustifyContent, LengthPercentage,
        LengthPercentageAuto, Overflow as TaffyOverflow, Position as TaffyPosition,
        Style as TaffyStyle,
    },
};

use crate::dom::{
    Align, ContentAlign, Dim, Display, FlexDir, FlexWrap, Lp, Overflow, Position, Style,
};

use super::engine::{LayoutEngine, MeasureFn, Rect};

// ─── Style mapping ───────────────────────────────────────────────────────────

/// Convert an inkferro `dom::Style` to a `taffy::Style`.
///
/// Mirrors the `apply*` functions in ink's `styles.ts`, reading every
/// group in the same order (styles.ts:415–777).  Divergences from yoga
/// are noted inline.
///
/// ### Percentage scale
/// ink/yoga use 0–100 (e.g. `parseInt("50%", 10)` → 50).  Taffy wants
/// 0.0–1.0.  All `Dim::Percent(p)` and `Lp::Percent(p)` values are
/// divided by 100 exactly once in this function.
pub fn style_to_taffy(s: &Style) -> TaffyStyle {
    TaffyStyle {
        // ── position (styles.ts:415–442) ──────────────────────────────────
        // Divergence: Yoga has POSITION_TYPE_STATIC; Taffy only has
        // Relative / Absolute.  `static` maps to Relative. The difference
        // is visible only when inset is set on a static node: yoga ignores
        // top/right/bottom/left for static (styles.ts:21), this mapping
        // honors them. Accepted: ink documents static as ignoring offsets
        // and Box never defaults to static.
        position: map_position(s.position),

        // ── inset / top/right/bottom/left (styles.ts:430–442) ─────────────
        inset: TaffyRect {
            top: map_dim_lpa(s.top.as_ref()),
            right: map_dim_lpa(s.right.as_ref()),
            bottom: map_dim_lpa(s.bottom.as_ref()),
            left: map_dim_lpa(s.left.as_ref()),
        },

        // ── margin (styles.ts:444–472) ────────────────────────────────────
        // Cascade: per-edge > axis shorthand > all shorthand (later yoga call
        // overrides earlier, so per-edge wins — mirrored with Option::or).
        margin: TaffyRect {
            top: map_lpa(
                s.margin_top
                    .as_ref()
                    .or(s.margin_y.as_ref())
                    .or(s.margin.as_ref()),
            ),
            bottom: map_lpa(
                s.margin_bottom
                    .as_ref()
                    .or(s.margin_y.as_ref())
                    .or(s.margin.as_ref()),
            ),
            left: map_lpa(
                s.margin_left
                    .as_ref()
                    .or(s.margin_x.as_ref())
                    .or(s.margin.as_ref()),
            ),
            right: map_lpa(
                s.margin_right
                    .as_ref()
                    .or(s.margin_x.as_ref())
                    .or(s.margin.as_ref()),
            ),
        },

        // ── padding (styles.ts:474–502) ───────────────────────────────────
        padding: TaffyRect {
            top: map_lp(
                s.padding_top
                    .as_ref()
                    .or(s.padding_y.as_ref())
                    .or(s.padding.as_ref()),
            ),
            bottom: map_lp(
                s.padding_bottom
                    .as_ref()
                    .or(s.padding_y.as_ref())
                    .or(s.padding.as_ref()),
            ),
            left: map_lp(
                s.padding_left
                    .as_ref()
                    .or(s.padding_x.as_ref())
                    .or(s.padding.as_ref()),
            ),
            right: map_lp(
                s.padding_right
                    .as_ref()
                    .or(s.padding_x.as_ref())
                    .or(s.padding.as_ref()),
            ),
        },

        // ── border (styles.ts:729–763) ────────────────────────────────────
        // borderWidth = 1 iff borderStyle is set (styles.ts:745).
        // Each edge = 0 if that edge is explicitly `false` (styles.ts:748-762).
        // Uses the shared Style::border_edges() helper — single source of truth
        // shared with the render clip inset in walk.rs.
        border: {
            let [top, right, bottom, left] = s.border_edges();
            TaffyRect {
                top: LengthPercentage::length(top as f32),
                right: LengthPercentage::length(right as f32),
                bottom: LengthPercentage::length(bottom as f32),
                left: LengthPercentage::length(left as f32),
            }
        },

        // ── flex (styles.ts:504–661) ──────────────────────────────────────
        // Box.tsx defaults (flexDirection:row, flexWrap:nowrap, flexGrow:0,
        // flexShrink:1) equal taffy's defaults, so None → taffy default is
        // correct with no special-casing needed.
        flex_direction: map_flex_dir(s.flex_direction),
        flex_wrap: map_flex_wrap(s.flex_wrap),
        flex_grow: s.flex_grow.unwrap_or(0.0),
        flex_shrink: s.flex_shrink.unwrap_or(1.0),
        flex_basis: map_dim(s.flex_basis.as_ref()),
        align_items: s.align_items.map(map_align_items),
        // alignSelf: taffy has no Auto variant — None encodes auto.
        align_self: s.align_self.map(map_align_self),
        // alignContent: Yoga's node default is flex-start (verified empirically
        // against ink's yoga-layout: getAlignContent() == ALIGN_FLEX_START),
        // while Taffy's None resolves to stretch. ink never sets alignContent
        // unless the prop is given (styles.ts), so None must map to FlexStart
        // or wrapped lines stretch/spread across the container cross axis.
        align_content: Some(
            s.align_content
                .map(map_content_align_content)
                .unwrap_or(AlignContent::FlexStart),
        ),
        justify_content: s.justify_content.map(map_content_align_justify),

        // ── dimensions (styles.ts:663–719) ────────────────────────────────
        size: Size {
            width: map_dim(s.width.as_ref()),
            height: map_dim(s.height.as_ref()),
        },
        // Divergence (width only): yoga ignores percent minWidth/maxWidth
        // (styles.ts:220/231, yoga#872); Taffy honors them. minHeight/
        // maxHeight percent is honored by BOTH — no divergence there
        // (styles.ts:225/236).  We map faithfully for all four fields.
        min_size: Size {
            width: map_dim(s.min_width.as_ref()),
            height: map_dim(s.min_height.as_ref()),
        },
        max_size: Size {
            width: map_dim(s.max_width.as_ref()),
            height: map_dim(s.max_height.as_ref()),
        },
        // aspectRatio: faithful f32 passthrough. Yoga-vs-Taffy resolution
        // order against size constraints is unverified; styles.ts:243
        // advises use with ≥1 size constraint.
        aspect_ratio: s.aspect_ratio,

        // ── display (styles.ts:721–727) ───────────────────────────────────
        display: map_display(s.display),

        // ── gap (styles.ts:765–777) ───────────────────────────────────────
        // Cascade: per-axis > all shorthand (column_gap/row_gap override gap).
        gap: Size {
            width: map_gap(s.column_gap.or(s.gap)),
            height: map_gap(s.row_gap.or(s.gap)),
        },

        // ── overflow (styles.ts; Box.tsx resolves shorthand JS-side) ──────
        overflow: Point {
            x: map_overflow(s.overflow_x),
            y: map_overflow(s.overflow_y),
        },

        // All remaining taffy fields (scrollbar_width, direction, etc.) not
        // present in ink's Styles type — use taffy defaults.
        ..Default::default()
    }
}

// ─── Mapping helpers (flat — ≤2 indent levels inside each fn) ────────────────

fn map_position(p: Option<Position>) -> TaffyPosition {
    match p.unwrap_or(Position::Relative) {
        Position::Absolute => TaffyPosition::Absolute,
        Position::Relative | Position::Static => TaffyPosition::Relative,
    }
}

fn map_dim(d: Option<&Dim>) -> Dimension {
    match d {
        None | Some(Dim::Auto) => Dimension::auto(),
        Some(Dim::Points(v)) => Dimension::length(*v),
        Some(Dim::Percent(p)) => Dimension::percent(p / 100.0),
    }
}

fn map_dim_lpa(d: Option<&Dim>) -> LengthPercentageAuto {
    match d {
        None | Some(Dim::Auto) => LengthPercentageAuto::auto(),
        Some(Dim::Points(v)) => LengthPercentageAuto::length(*v),
        Some(Dim::Percent(p)) => LengthPercentageAuto::percent(p / 100.0),
    }
}

fn map_lp(lp: Option<&Lp>) -> LengthPercentage {
    match lp {
        None => LengthPercentage::length(0.0),
        Some(Lp::Points(v)) => LengthPercentage::length(*v),
        Some(Lp::Percent(p)) => LengthPercentage::percent(p / 100.0),
    }
}

/// Margin edges: `None` → `0` (yoga default for unset margins).
/// Do NOT use `auto()` here — taffy auto-margins distribute free space,
/// producing centering that ink never exhibits on unset margins.
fn map_lpa(lp: Option<&Lp>) -> LengthPercentageAuto {
    match lp {
        // Yoga default for unset margins is 0, not auto.  Taffy auto margins
        // distribute free space (centering effect) — must not use auto for None.
        None => LengthPercentageAuto::length(0.0),
        Some(Lp::Points(v)) => LengthPercentageAuto::length(*v),
        Some(Lp::Percent(p)) => LengthPercentageAuto::percent(p / 100.0),
    }
}

fn map_flex_dir(d: Option<FlexDir>) -> FlexDirection {
    match d.unwrap_or(FlexDir::Row) {
        FlexDir::Row => FlexDirection::Row,
        FlexDir::Column => FlexDirection::Column,
        FlexDir::RowReverse => FlexDirection::RowReverse,
        FlexDir::ColumnReverse => FlexDirection::ColumnReverse,
    }
}

fn map_flex_wrap(w: Option<FlexWrap>) -> TaffyFlexWrap {
    match w.unwrap_or(FlexWrap::NoWrap) {
        FlexWrap::NoWrap => TaffyFlexWrap::NoWrap,
        FlexWrap::Wrap => TaffyFlexWrap::Wrap,
        FlexWrap::WrapReverse => TaffyFlexWrap::WrapReverse,
    }
}

fn map_align_items(a: Align) -> AlignItems {
    match a {
        Align::Stretch => AlignItems::Stretch,
        Align::FlexStart => AlignItems::FlexStart,
        Align::Center => AlignItems::Center,
        Align::FlexEnd => AlignItems::FlexEnd,
        Align::Baseline => AlignItems::Baseline,
    }
}

fn map_align_self(a: Align) -> AlignSelf {
    match a {
        Align::Stretch => AlignSelf::Stretch,
        Align::FlexStart => AlignSelf::FlexStart,
        Align::Center => AlignSelf::Center,
        Align::FlexEnd => AlignSelf::FlexEnd,
        Align::Baseline => AlignSelf::Baseline,
    }
}

fn map_content_align_content(c: ContentAlign) -> AlignContent {
    match c {
        ContentAlign::FlexStart => AlignContent::FlexStart,
        ContentAlign::Center => AlignContent::Center,
        ContentAlign::FlexEnd => AlignContent::FlexEnd,
        ContentAlign::SpaceBetween => AlignContent::SpaceBetween,
        ContentAlign::SpaceAround => AlignContent::SpaceAround,
        ContentAlign::SpaceEvenly => AlignContent::SpaceEvenly,
        ContentAlign::Stretch => AlignContent::Stretch,
    }
}

fn map_content_align_justify(c: ContentAlign) -> JustifyContent {
    match c {
        ContentAlign::FlexStart => JustifyContent::FlexStart,
        ContentAlign::Center => JustifyContent::Center,
        ContentAlign::FlexEnd => JustifyContent::FlexEnd,
        ContentAlign::SpaceBetween => JustifyContent::SpaceBetween,
        ContentAlign::SpaceAround => JustifyContent::SpaceAround,
        ContentAlign::SpaceEvenly => JustifyContent::SpaceEvenly,
        ContentAlign::Stretch => JustifyContent::Stretch,
    }
}

fn map_display(d: Option<Display>) -> TaffyDisplay {
    match d.unwrap_or(Display::Flex) {
        Display::Flex => TaffyDisplay::Flex,
        Display::None => TaffyDisplay::None,
    }
}

fn map_gap(g: Option<f32>) -> LengthPercentage {
    match g {
        None => LengthPercentage::length(0.0),
        Some(v) => LengthPercentage::length(v),
    }
}

fn map_overflow(o: Option<Overflow>) -> TaffyOverflow {
    match o.unwrap_or(Overflow::Visible) {
        Overflow::Visible => TaffyOverflow::Visible,
        Overflow::Hidden => TaffyOverflow::Hidden,
    }
}

// ─── TaffyEngine ─────────────────────────────────────────────────────────────

/// Taffy 0.10 backend.
///
/// Invariant: every dom id in `id_map` has a valid `NodeId` in `tree`.
pub struct TaffyEngine {
    /// The taffy tree (flexbox layout).  Taffy's built-in rounding is DISABLED
    /// at construction (`disable_rounding`); `calculate` runs a Yoga-compatible
    /// pixel-grid post-pass instead (see `round_layout_yoga` / `mod.rs`).
    /// Each node's context is the dom id (`u32`) so the measure closure can
    /// dispatch into `measures` without a secondary reverse map.
    tree: TaffyTree<u32>,

    /// dom id → taffy NodeId.
    id_map: HashMap<u32, NodeId>,

    /// Measure callbacks keyed by dom id.  Populated by `set_measure`; called
    /// by the closure passed to `compute_layout_with_measure`.  A registered
    /// measure marks the node as a Yoga "Text" node for rounding purposes
    /// (`PixelGrid.cpp` `node->getNodeType() == NodeType::Text`).
    measures: HashMap<u32, Box<MeasureFn>>,

    /// Rounded, parent-relative rects keyed by dom id, produced by the
    /// Yoga-compatible post-pass at the end of `calculate`.  `computed` reads
    /// from here; it falls back to the live (unrounded) taffy layout for ids
    /// not present (e.g. a node created but never laid out).
    rounded: HashMap<u32, Rect>,

    /// Rounded, ABSOLUTE (root-relative) rects keyed by dom id — the same
    /// post-pass also accumulates the rounded parent-relative offsets down the
    /// recursion (the renderer paints each node at exactly this sum, and the
    /// jacob314/ink fork's `getBoundingBox` computes the same sum by walking
    /// `getComputedLeft/Top` up the parent chain).  `computed_absolute` reads
    /// from here.  ADDITIVE alongside `rounded`: the parent-relative map and
    /// `computed`'s contract are unchanged.
    rounded_absolute: HashMap<u32, Rect>,
}

impl TaffyEngine {
    /// Create an empty engine.
    pub fn new() -> Self {
        let mut tree = TaffyTree::new();
        // Disable taffy's cumulative round-half-away rounding; we apply Yoga's
        // pixel-grid rounding in `round_layout_yoga` after each `calculate`, so
        // tie-breaks and text-node floor/ceil match ink's yoga 3.2.1 exactly.
        tree.disable_rounding();
        Self {
            tree,
            id_map: HashMap::new(),
            measures: HashMap::new(),
            rounded: HashMap::new(),
            rounded_absolute: HashMap::new(),
        }
    }

    /// Resolve `dom_id` to a taffy `NodeId`.
    fn taffy_id(&self, dom_id: u32) -> Result<NodeId, String> {
        self.id_map
            .get(&dom_id)
            .copied()
            .ok_or_else(|| format!("layout: unknown dom id {dom_id}"))
    }

    /// The node's rounded ABSOLUTE (root-relative) rect — `x`/`y` are the sum
    /// of the rounded parent-relative offsets down the ancestor chain (the
    /// integer cell where the renderer paints the node); `width`/`height` are
    /// identical to [`LayoutEngine::computed`]'s.
    ///
    /// ADDITIVE companion to `computed` (which stays parent-relative —
    /// wire/API covenant): produced by the same `round_node` post-pass, so the
    /// two are coherent per `calculate`.  Returns `None` for unknown, freed,
    /// or never-calculated ids.  A node detached AFTER the last `calculate`
    /// (`remove_child` without `destroy`) serves its last-calculated rect
    /// until the next `calculate` evicts it — the same staleness contract as
    /// `rounded` (see `destroy`'s eviction note).  No live-taffy fallback
    /// like `computed`'s: an absolute position requires the ancestor chain
    /// walked by `calculate`, which a not-yet-calculated node does not have.
    /// The rendered path (build → `calculate` → read) never hits that case.
    pub fn computed_absolute(&self, id: u32) -> Option<Rect> {
        self.rounded_absolute.get(&id).copied()
    }
}

// ─── Yoga-compatible pixel-grid rounding (yoga 3.2.1 PixelGrid.cpp) ───────────
//
// Ink uses yoga-layout 3.2.1 (ink/package.json: "yoga-layout": "~3.2.1").  Yoga
// rounds layout results to the pixel grid *after* the flex solve, in
// `roundLayoutResultsToPixelGrid` (yoga/algorithm/PixelGrid.cpp), using
// `roundValueToPixelGrid` for the actual half-up / floor / ceil decision.  Taffy
// 0.10 rounds differently (cumulative round-half-away in `compute::round_layout`,
// compute/mod.rs:219), which diverges from yoga by ±1 on tie-breaks and on
// text-node sizing.  We disable taffy rounding and port yoga's algorithm here so
// our integer rects match ink cell-for-cell.
//
// `pointScaleFactor` is 1.0 for terminals (one cell == one "point"); we hardcode
// it and drop the `* pointScaleFactor` / `/ pointScaleFactor` no-ops.  All math
// is done in f64 (yoga uses `double` throughout PixelGrid.cpp) and only narrowed
// to integer cells at the very end.

/// Yoga's `inexactEquals(double, double)` — yoga/numeric/Comparison.h:
/// `std::abs(a - b) < 0.0001`.  (Both args are always defined here, so the
/// undefined-handling branch is omitted.)
fn inexact_equals(a: f64, b: f64) -> bool {
    (a - b).abs() < 0.0001
}

/// Port of yoga 3.2.1 `roundValueToPixelGrid` (PixelGrid.cpp), specialized to
/// `pointScaleFactor == 1.0`.
///
/// ```text
/// double scaledValue = value;            // value * 1.0
/// double fractial = fmod(scaledValue, 1.0);
/// if (fractial < 0) ++fractial;          // make fractial in [0,1) even for value<0
/// if      (inexactEquals(fractial, 0.0)) scaledValue -= fractial;        // already whole
/// else if (inexactEquals(fractial, 1.0)) scaledValue += 1.0 - fractial;  // ~whole below
/// else if (forceCeil)  scaledValue += 1.0 - fractial;                    // ceil
/// else if (forceFloor) scaledValue -= fractial;                          // floor
/// else                 scaledValue += (fractial > 0.5 || inexactEquals(fractial, 0.5))
///                                          ? (1.0 - fractial) : -fractial; // round half up
/// return scaledValue;                    // / 1.0
/// ```
fn round_value_to_pixel_grid(value: f64, force_ceil: bool, force_floor: bool) -> f64 {
    let mut scaled = value;
    // fmod keeps the sign of the dividend (matches C++ fmod): e.g.
    // fmod(-2.2, 1.0) == -0.2.  Add 1 so `scaled - fractial == floor(scaled)`
    // for negatives too (PixelGrid.cpp comment).
    let mut fractial = scaled % 1.0;
    if fractial < 0.0 {
        fractial += 1.0;
    }
    // Yoga's PixelGrid.cpp branches in this exact order (order matters — e.g.
    // `fractial ≈ 1.0` must ceil even when `force_floor` is set):
    //   1. fractial ≈ 0.0        → floor (already whole):       scaled -= fractial
    //   2. fractial ≈ 1.0        → ceil  (whole, just below):   scaled += 1 - fractial
    //   3. forceCeil             → ceil:                        scaled += 1 - fractial
    //   4. forceFloor            → floor:                       scaled -= fractial
    //   5. else (round half up)  → +1 iff fractial >= 0.5, else +0
    //
    // We preserve that order exactly.  To satisfy clippy's `if_same_then_else`
    // without reordering, the arithmetic is expressed as a single delta computed
    // in yoga's priority order, then applied once.
    let delta = if inexact_equals(fractial, 0.0) {
        // (1) already whole → floor
        -fractial
    } else if inexact_equals(fractial, 1.0) || force_ceil {
        // (2)/(3) ~whole-just-below or forced ceil → round up
        1.0 - fractial
    } else if force_floor {
        // (4) forced floor (text nodes never round down)
        -fractial
    } else if fractial > 0.5 || inexact_equals(fractial, 0.5) {
        // (5) round half up — exactly-0.5 ties go toward +inf, matching yoga
        1.0 - fractial
    } else {
        // (5) round half down
        -fractial
    };
    scaled += delta;
    scaled
}

/// Parent origins threaded through `round_node`'s recursion.
///
/// `absolute_left`/`absolute_top` are yoga's `absoluteLeft`/`absoluteTop` —
/// the *unrounded* absolute offset of the parent, used only for the
/// edge-rounding of dimensions.  `rounded_left`/`rounded_top` are the sum of
/// the ROUNDED parent-relative offsets of all ancestors — the integer cell
/// origin the renderer actually paints the parent at — used to accumulate the
/// absolute rects (`TaffyEngine::rounded_absolute`).
struct RoundOrigin {
    absolute_left: f64,
    absolute_top: f64,
    rounded_left: i32,
    rounded_top: i32,
}

/// Recursive port of yoga 3.2.1 `roundLayoutResultsToPixelGrid` (PixelGrid.cpp),
/// specialized to `pointScaleFactor == 1.0`.
///
/// `absolute_left` / `absolute_top` are the *unrounded* absolute offsets of this
/// node's parent (yoga threads these through the recursion).  We compute each
/// node's rounded parent-relative position and rounded dimension and store the
/// result keyed by dom id; the renderer re-accumulates absolute offsets from the
/// parent-relative rects, so storing parent-relative here matches yoga's
/// `setLayoutPosition` (which overwrites the *relative* position).
///
/// `is_text(dom_id)` is true iff the node has a measure fn registered — that is
/// our equivalent of yoga's `node->getNodeType() == NodeType::Text`, the flag
/// yoga uses to floor (never round down) text positions/sizes so glyphs are not
/// truncated.
fn round_node(
    tree: &TaffyTree<u32>,
    is_text: &dyn Fn(u32) -> bool,
    nid: NodeId,
    dom_id: u32,
    origin: RoundOrigin,
    out: &mut HashMap<u32, Rect>,
    out_absolute: &mut HashMap<u32, Rect>,
) {
    let RoundOrigin {
        absolute_left,
        absolute_top,
        rounded_left,
        rounded_top,
    } = origin;
    // Read the unrounded layout taffy produced for this node.
    let Ok(layout) = tree.layout(nid) else {
        return;
    };
    let node_left = f64::from(layout.location.x);
    let node_top = f64::from(layout.location.y);
    let node_width = f64::from(layout.size.width);
    let node_height = f64::from(layout.size.height);

    let absolute_node_left = absolute_left + node_left;
    let absolute_node_top = absolute_top + node_top;
    let absolute_node_right = absolute_node_left + node_width;
    let absolute_node_bottom = absolute_node_top + node_height;

    // pointScaleFactor (== 1.0) is never 0, so we always take yoga's rounding
    // branch.  textRounding: yoga floors text nodes so they never shrink below
    // their measured glyph extent (PixelGrid.cpp).
    let text_rounding = is_text(dom_id);

    // Position: parent-relative, rounded from the *relative* nodeLeft/nodeTop
    // (PixelGrid.cpp: roundValueToPixelGrid(nodeLeft, …, forceFloor=textRounding)).
    let rx = round_value_to_pixel_grid(node_left, false, text_rounding);
    let ry = round_value_to_pixel_grid(node_top, false, text_rounding);

    // Dimensions: round(absoluteRight) - round(absoluteLeft) so cumulative edges
    // line up with neighbors.  For text nodes, ceil when there is a fractional
    // remainder and floor otherwise (PixelGrid.cpp hasFractionalWidth/Height).
    let has_fractional_width =
        !inexact_equals(node_width % 1.0, 0.0) && !inexact_equals(node_width % 1.0, 1.0);
    let has_fractional_height =
        !inexact_equals(node_height % 1.0, 0.0) && !inexact_equals(node_height % 1.0, 1.0);

    let rw = round_value_to_pixel_grid(
        absolute_node_right,
        text_rounding && has_fractional_width,
        text_rounding && !has_fractional_width,
    ) - round_value_to_pixel_grid(absolute_node_left, false, text_rounding);
    let rh = round_value_to_pixel_grid(
        absolute_node_bottom,
        text_rounding && has_fractional_height,
        text_rounding && !has_fractional_height,
    ) - round_value_to_pixel_grid(absolute_node_top, false, text_rounding);

    let rect = Rect {
        x: rx.round() as i32,
        y: ry.round() as i32,
        width: rw.max(0.0).round() as u16,
        height: rh.max(0.0).round() as u16,
    };
    out.insert(dom_id, rect);

    // Absolute (root-relative) position: the sum of the ROUNDED parent-relative
    // offsets down the ancestor chain — exactly where the renderer paints this
    // node (it re-accumulates the rounded relative rects), and exactly what the
    // jacob314/ink fork's `getBoundingBox` computes by summing yoga's
    // `getComputedLeft/Top` (post-pixel-grid values) up `parentNode`.  NOT
    // `round(absolute_node_left)` — rounding the unrounded absolute can differ
    // by ±1 from the painted position on fractional ancestors.
    let abs_x = rounded_left + rect.x;
    let abs_y = rounded_top + rect.y;
    out_absolute.insert(
        dom_id,
        Rect {
            x: abs_x,
            y: abs_y,
            ..rect
        },
    );

    // Recurse with this node's *unrounded* absolute origin (yoga passes
    // absoluteNodeLeft/absoluteNodeTop, not the rounded values) plus the
    // rounded painted origin for the absolute-rect accumulation.
    let child_count = tree.child_count(nid);
    for index in 0..child_count {
        let Ok(child_nid) = tree.child_at_index(nid, index) else {
            continue;
        };
        // The dom id is the node's taffy context.
        let Some(child_dom) = tree.get_node_context(child_nid).copied() else {
            continue;
        };
        round_node(
            tree,
            is_text,
            child_nid,
            child_dom,
            RoundOrigin {
                absolute_left: absolute_node_left,
                absolute_top: absolute_node_top,
                rounded_left: abs_x,
                rounded_top: abs_y,
            },
            out,
            out_absolute,
        );
    }
}

impl Default for TaffyEngine {
    fn default() -> Self {
        Self::new()
    }
}

impl LayoutEngine for TaffyEngine {
    fn create(&mut self, id: u32) -> Result<(), String> {
        // Idempotent: if already present, no-op (mirrors dom Create no-op on
        // an occupied slot — `arena.rs:30-32`).
        if self.id_map.contains_key(&id) {
            return Ok(());
        }
        // Store the dom id as the node's context so the measure closure can
        // read it directly from the `ctx` parameter — no reverse map needed.
        let nid = self
            .tree
            .new_leaf_with_context(TaffyStyle::default(), id)
            .map_err(|e| e.to_string())?;
        self.id_map.insert(id, nid);
        Ok(())
    }

    fn apply_style(&mut self, id: u32, style: &Style) -> Result<(), String> {
        let nid = self.taffy_id(id)?;
        self.tree
            .set_style(nid, style_to_taffy(style))
            .map_err(|e| e.to_string())
    }

    fn set_measure(&mut self, id: u32, f: Box<MeasureFn>) {
        // Store; dispatched during `calculate`.  The dom id is available via
        // the node's taffy context (`TaffyTree<u32>`), so no reverse map is
        // needed here or in `calculate`.
        self.measures.insert(id, f);
    }

    fn insert_child(&mut self, parent: u32, child: u32, index: usize) -> Result<(), String> {
        let pnid = self.taffy_id(parent)?;
        let cnid = self.taffy_id(child)?;

        let child_count = self.tree.child_count(pnid);
        if index >= child_count {
            // Clamp to append — callers with a stale index must not panic.
            self.tree.add_child(pnid, cnid).map_err(|e| e.to_string())
        } else {
            self.tree
                .insert_child_at_index(pnid, index, cnid)
                .map_err(|e| e.to_string())
        }
    }

    fn remove_child(&mut self, parent: u32, child: u32) -> Result<(), String> {
        let pnid = self.taffy_id(parent)?;
        let cnid = self.taffy_id(child)?;
        self.tree
            .remove_child(pnid, cnid)
            .map(|_| ())
            .map_err(|e| e.to_string())
    }

    fn destroy(&mut self, id: u32) {
        // Look up the taffy NodeId; silently no-op if not present.
        let Some(nid) = self.id_map.remove(&id) else {
            return;
        };
        // Drop any measure function registered for this dom id.
        self.measures.remove(&id);
        // Evict from the rounded map so computed() cannot serve a stale rect
        // after the node is destroyed (violates the destroy→computed-None
        // contract).  Note: remove_child (detach without destroy) intentionally
        // does NOT evict — a detached-but-alive node retains its last-calculated
        // rect until the next calculate(), matching yoga's behavior (yoga also
        // serves the last layout for detached nodes until recompute).
        self.rounded.remove(&id);
        self.rounded_absolute.remove(&id);
        // Taffy 0.10 `remove` detaches the node from its parent and children
        // (children become orphan taffy leaves — their Free ops arrive
        // separately; see Free-no-cascade in dom/mod.rs).  Errors are swallowed
        // because a missing NodeId is a bug, not a recoverable condition here.
        let _ = self.tree.remove(nid);
    }

    fn mark_dirty(&mut self, id: u32) -> Result<(), String> {
        let nid = self.taffy_id(id)?;
        self.tree.mark_dirty(nid).map_err(|e| e.to_string())
    }

    fn calculate(
        &mut self,
        root_id: u32,
        viewport_width: f32,
        viewport_height: Option<f32>,
    ) -> Result<(), String> {
        let root_nid = self.taffy_id(root_id)?;

        // ink render-to-string.ts:62 — rootNode.yogaNode!.setWidth(columns).
        // The root container is given a DEFINITE width equal to the terminal
        // columns so no-width children stretch to fill it (instead of the root
        // shrink-wrapping to content under an auto width).
        // The other half of ink-root identity (column/stretch defaults) lives
        // in render::create_layout_nodes, which sees node kinds.
        if let Ok(mut s) = self.tree.style(root_nid).cloned() {
            s.size.width = Dimension::length(viewport_width);
            let _ = self.tree.set_style(root_nid, s);
        }

        // viewport_height: None → MaxContent (unconstrained, render-to-string.ts:62-68).
        let available = Size {
            width: AvailableSpace::Definite(viewport_width),
            height: match viewport_height {
                Some(h) => AvailableSpace::Definite(h),
                None => AvailableSpace::MaxContent,
            },
        };

        // Taffy 0.10 passes the node's context (`&mut u32` dom id) directly to
        // the measure closure — no reverse-map snapshot needed.  `ctx` is a
        // parameter, not a capture, so borrowing `self.measures` here does not
        // conflict with the `&mut self.tree` borrow held by taffy.
        self.tree
            .compute_layout_with_measure(root_nid, available, |known, avail, _nid, ctx, _style| {
                // `ctx` is `Option<&mut u32>` — the dom id stored on the node.
                if let Some(&mut did) = ctx
                    && let Some(f) = self.measures.get_mut(&did)
                {
                    return f(known, avail);
                }
                // No measure function registered → zero size (leaf with no
                // intrinsic size, e.g. a box with only flex children).
                Size::ZERO
            })
            .map_err(|e| e.to_string())?;

        // Yoga-compatible pixel-grid rounding post-pass.  Taffy's own rounding
        // is disabled (see `new`); we round the unrounded float layout exactly
        // like yoga 3.2.1 `roundLayoutResultsToPixelGrid` so integer cell rects
        // match ink.  Rebuild the map each calculate; the root recursion starts
        // at absolute (0.0, 0.0) (yoga calls it with absoluteLeft/Top = 0).
        self.rounded.clear();
        self.rounded_absolute.clear();
        let is_text = |dom_id: u32| self.measures.contains_key(&dom_id);
        round_node(
            &self.tree,
            &is_text,
            root_nid,
            root_id,
            RoundOrigin {
                absolute_left: 0.0,
                absolute_top: 0.0,
                rounded_left: 0,
                rounded_top: 0,
            },
            &mut self.rounded,
            &mut self.rounded_absolute,
        );
        Ok(())
    }

    fn computed(&self, id: u32) -> Option<Rect> {
        // Primary path: the Yoga-compatible rounded rect produced by the
        // post-pass in `calculate` (see `round_node`).  Parent-relative, integer
        // cells — same contract as before.
        if let Some(r) = self.rounded.get(&id) {
            return Some(*r);
        }

        // Fallback: a node that was created but never laid out (no `calculate`
        // covering it yet).  Return the live taffy layout, truncated.  Taffy's
        // own rounding is disabled, so these floats are unrounded; truncation
        // here is a best-effort placeholder for the not-yet-calculated case and
        // is never hit on the rendered path (which always runs `calculate`).
        // Detached-but-alive nodes (remove_child without destroy) also land here
        // after the next calculate() evicts them from `rounded` — they retain
        // their last-calculated rect from `tree.layout()` until recompute, which
        // matches yoga's behavior of serving the last layout for detached nodes.
        let nid = self.id_map.get(&id).copied()?;
        let lay = self.tree.layout(nid).ok()?;
        Some(Rect {
            x: lay.location.x as i32,
            y: lay.location.y as i32,
            width: lay.size.width as u16,
            height: lay.size.height as u16,
        })
    }
}

// ─── Tests ───────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;
    use crate::dom::BorderStyle;
    use taffy::style::FlexDirection as TFD;

    fn pt(v: f32) -> Dimension {
        Dimension::length(v)
    }

    /// Convenience: create a TaffyEngine with `ids` pre-registered.
    fn engine_with(ids: &[u32]) -> TaffyEngine {
        let mut e = TaffyEngine::new();
        for &id in ids {
            e.create(id).unwrap();
        }
        e
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Style mapping unit tests (prop-group by prop-group)
    // ═══════════════════════════════════════════════════════════════════════════

    // ── M1. position (styles.ts:415–442) ────────────────────────────────────
    #[test]
    fn map_position_absolute() {
        let s = Style {
            position: Some(Position::Absolute),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).position, TaffyPosition::Absolute);
    }

    #[test]
    fn map_position_relative() {
        let s = Style {
            position: Some(Position::Relative),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).position, TaffyPosition::Relative);
    }

    #[test]
    fn map_position_static_maps_to_relative() {
        // Divergence: Taffy has no Static; map to Relative.
        let s = Style {
            position: Some(Position::Static),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).position, TaffyPosition::Relative);
    }

    #[test]
    fn map_inset_points() {
        let s = Style {
            top: Some(Dim::Points(2.0)),
            left: Some(Dim::Points(5.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.inset.top, LengthPercentageAuto::length(2.0));
        assert_eq!(t.inset.left, LengthPercentageAuto::length(5.0));
        assert_eq!(t.inset.right, LengthPercentageAuto::auto());
        assert_eq!(t.inset.bottom, LengthPercentageAuto::auto());
    }

    #[test]
    fn map_inset_percent() {
        let s = Style {
            top: Some(Dim::Percent(50.0)),
            ..Default::default()
        };
        // 50% → 0.5 in taffy
        assert_eq!(
            style_to_taffy(&s).inset.top,
            LengthPercentageAuto::percent(0.5)
        );
    }

    // ── M2. margin cascade (styles.ts:444–472) ───────────────────────────────
    // Hand-derived: margin_all=2, margin_x=4, margin_left=7.
    // Expected: top=2, bottom=2, right=4, left=7.
    #[test]
    fn map_margin_cascade() {
        let s = Style {
            margin: Some(Lp::Points(2.0)),
            margin_x: Some(Lp::Points(4.0)),
            margin_left: Some(Lp::Points(7.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.margin.top, LengthPercentageAuto::length(2.0));
        assert_eq!(t.margin.bottom, LengthPercentageAuto::length(2.0));
        assert_eq!(t.margin.right, LengthPercentageAuto::length(4.0));
        assert_eq!(t.margin.left, LengthPercentageAuto::length(7.0));
    }

    #[test]
    fn map_margin_y_shorthand() {
        let s = Style {
            margin: Some(Lp::Points(1.0)),
            margin_y: Some(Lp::Points(3.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.margin.top, LengthPercentageAuto::length(3.0));
        assert_eq!(t.margin.bottom, LengthPercentageAuto::length(3.0));
        assert_eq!(t.margin.left, LengthPercentageAuto::length(1.0));
        assert_eq!(t.margin.right, LengthPercentageAuto::length(1.0));
    }

    #[test]
    fn map_margin_percent() {
        // Yoga/ink convention: 50 means 50%; taffy needs 0.5.
        let s = Style {
            margin: Some(Lp::Percent(50.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.margin.top, LengthPercentageAuto::percent(0.5));
    }

    // ── M3. padding cascade (styles.ts:474–502) ──────────────────────────────
    #[test]
    fn map_padding_cascade() {
        let s = Style {
            padding: Some(Lp::Points(2.0)),
            padding_x: Some(Lp::Points(4.0)),
            padding_top: Some(Lp::Points(1.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.padding.top, LengthPercentage::length(1.0));
        assert_eq!(t.padding.bottom, LengthPercentage::length(2.0));
        assert_eq!(t.padding.left, LengthPercentage::length(4.0));
        assert_eq!(t.padding.right, LengthPercentage::length(4.0));
    }

    // ── M4. flex (styles.ts:504–661) ─────────────────────────────────────────
    #[test]
    fn map_flex_direction_column() {
        let s = Style {
            flex_direction: Some(FlexDir::Column),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).flex_direction, FlexDirection::Column);
    }

    #[test]
    fn map_flex_direction_row_reverse() {
        let s = Style {
            flex_direction: Some(FlexDir::RowReverse),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).flex_direction, FlexDirection::RowReverse);
    }

    #[test]
    fn map_flex_wrap() {
        let s = Style {
            flex_wrap: Some(FlexWrap::Wrap),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).flex_wrap, TaffyFlexWrap::Wrap);
    }

    #[test]
    fn map_flex_grow_shrink() {
        let s = Style {
            flex_grow: Some(2.0),
            flex_shrink: Some(0.5),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.flex_grow, 2.0);
        assert_eq!(t.flex_shrink, 0.5);
    }

    #[test]
    fn map_flex_basis_points() {
        let s = Style {
            flex_basis: Some(Dim::Points(40.0)),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).flex_basis, Dimension::length(40.0));
    }

    #[test]
    fn map_flex_basis_percent() {
        // ink passes 50 for "50%"; taffy needs 0.5.
        let s = Style {
            flex_basis: Some(Dim::Percent(50.0)),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).flex_basis, Dimension::percent(0.5));
    }

    #[test]
    fn map_flex_basis_auto() {
        let s = Style {
            flex_basis: Some(Dim::Auto),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).flex_basis, Dimension::auto());
    }

    #[test]
    fn map_align_items_center() {
        let s = Style {
            align_items: Some(Align::Center),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).align_items, Some(AlignItems::Center));
    }

    #[test]
    fn map_align_self_none_is_auto() {
        // align_self: None in dom::Style → None in taffy (encodes auto).
        let s = Style {
            align_self: None,
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).align_self, None);
    }

    #[test]
    fn map_align_content_space_between() {
        let s = Style {
            align_content: Some(ContentAlign::SpaceBetween),
            ..Default::default()
        };
        assert_eq!(
            style_to_taffy(&s).align_content,
            Some(AlignContent::SpaceBetween)
        );
    }

    #[test]
    fn map_justify_content_center() {
        let s = Style {
            justify_content: Some(ContentAlign::Center),
            ..Default::default()
        };
        assert_eq!(
            style_to_taffy(&s).justify_content,
            Some(JustifyContent::Center)
        );
    }

    // ── M5. dimensions (styles.ts:663–719) ───────────────────────────────────
    // Oracle case 1 (hand-derived): width=80, height=24 → fixed terminal size.
    // A flex root with explicit 80×24 should report exactly 80×24 after layout.
    #[test]
    fn map_width_height_points() {
        let s = Style {
            width: Some(Dim::Points(80.0)),
            height: Some(Dim::Points(24.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.size.width, Dimension::length(80.0));
        assert_eq!(t.size.height, Dimension::length(24.0));
    }

    #[test]
    fn map_width_percent() {
        let s = Style {
            width: Some(Dim::Percent(50.0)),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).size.width, Dimension::percent(0.5));
    }

    #[test]
    fn map_width_auto() {
        let s = Style {
            width: Some(Dim::Auto),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).size.width, Dimension::auto());
    }

    #[test]
    fn map_min_max_size() {
        let s = Style {
            min_width: Some(Dim::Points(10.0)),
            max_width: Some(Dim::Points(100.0)),
            min_height: Some(Dim::Points(5.0)),
            max_height: Some(Dim::Points(50.0)),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.min_size.width, Dimension::length(10.0));
        assert_eq!(t.max_size.width, Dimension::length(100.0));
        assert_eq!(t.min_size.height, Dimension::length(5.0));
        assert_eq!(t.max_size.height, Dimension::length(50.0));
    }

    #[test]
    fn map_aspect_ratio() {
        let s = Style {
            aspect_ratio: Some(16.0 / 9.0),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert!((t.aspect_ratio.unwrap() - 16.0 / 9.0).abs() < f32::EPSILON);
    }

    // ── M6. display (styles.ts:721–727) ──────────────────────────────────────
    #[test]
    fn map_display_flex() {
        let s = Style {
            display: Some(Display::Flex),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).display, TaffyDisplay::Flex);
    }

    #[test]
    fn map_display_none() {
        let s = Style {
            display: Some(Display::None),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).display, TaffyDisplay::None);
    }

    // ── M7. border (styles.ts:729–763) ───────────────────────────────────────
    // Oracle case 2 (hand-derived): borderStyle="single" with no per-edge
    // overrides → all four edges = 1 cell.  A 10×5 box with border has
    // content area 8×3 (1 cell consumed each side).
    #[test]
    fn map_border_all_edges_active() {
        let s = Style {
            border_style: Some(BorderStyle::Named("single".into())),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.border.top, LengthPercentage::length(1.0));
        assert_eq!(t.border.right, LengthPercentage::length(1.0));
        assert_eq!(t.border.bottom, LengthPercentage::length(1.0));
        assert_eq!(t.border.left, LengthPercentage::length(1.0));
    }

    #[test]
    fn map_border_top_disabled() {
        let s = Style {
            border_style: Some(BorderStyle::Named("single".into())),
            border_top: Some(false),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.border.top, LengthPercentage::length(0.0));
        assert_eq!(t.border.bottom, LengthPercentage::length(1.0));
        assert_eq!(t.border.left, LengthPercentage::length(1.0));
        assert_eq!(t.border.right, LengthPercentage::length(1.0));
    }

    #[test]
    fn map_border_none_when_no_border_style() {
        let s = Style {
            border_style: None,
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.border.top, LengthPercentage::length(0.0));
        assert_eq!(t.border.right, LengthPercentage::length(0.0));
        assert_eq!(t.border.bottom, LengthPercentage::length(0.0));
        assert_eq!(t.border.left, LengthPercentage::length(0.0));
    }

    // ── M8. gap (styles.ts:765–777) ──────────────────────────────────────────
    // Oracle case 3 (hand-derived): gap=2 with two 10×5 children in a row
    // inside an 80×5 container.  Expected: c1.x=0, c2.x=12 (10+2 gap).
    #[test]
    fn map_gap_all() {
        let s = Style {
            gap: Some(2.0),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.gap.width, LengthPercentage::length(2.0));
        assert_eq!(t.gap.height, LengthPercentage::length(2.0));
    }

    #[test]
    fn map_gap_per_axis() {
        let s = Style {
            column_gap: Some(4.0),
            row_gap: Some(1.0),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.gap.width, LengthPercentage::length(4.0));
        assert_eq!(t.gap.height, LengthPercentage::length(1.0));
    }

    #[test]
    fn map_gap_per_axis_overrides_all() {
        // column_gap=4 wins over gap=2 for the horizontal axis.
        let s = Style {
            gap: Some(2.0),
            column_gap: Some(4.0),
            ..Default::default()
        };
        let t = style_to_taffy(&s);
        assert_eq!(t.gap.width, LengthPercentage::length(4.0));
        assert_eq!(t.gap.height, LengthPercentage::length(2.0));
    }

    // ── M9. overflow (styles.ts; Box.tsx resolves shorthand JS-side) ──────────
    #[test]
    fn map_overflow_hidden() {
        let s = Style {
            overflow_x: Some(Overflow::Hidden),
            ..Default::default()
        };
        assert_eq!(style_to_taffy(&s).overflow.x, TaffyOverflow::Hidden);
        assert_eq!(style_to_taffy(&s).overflow.y, TaffyOverflow::Visible);
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // End-to-end layout tests through apply_style (engine trait path)
    // ═══════════════════════════════════════════════════════════════════════════

    // ── E1. apply_style width/height end-to-end ───────────────────────────────
    // Oracle case 1 (hand-derived): root at 80×24 via apply_style.
    // Flexbox: a node with explicit size fills exactly that size.
    #[test]
    fn apply_style_width_height() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();
        let s = Style {
            width: Some(Dim::Points(80.0)),
            height: Some(Dim::Points(24.0)),
            ..Default::default()
        };
        e.apply_style(0, &s).unwrap();
        e.calculate(0, 80.0, Some(24.0)).unwrap();
        assert_eq!(
            e.computed(0).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 24
            }
        );
    }

    // ── E2. apply_style flexDirection end-to-end ──────────────────────────────
    // Oracle case 3 (hand-derived): column layout; two 80×12 children at y=0 and y=12.
    #[test]
    fn apply_style_flex_direction_column() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(0, 2, 1).unwrap();

        e.apply_style(
            0,
            &Style {
                width: Some(Dim::Points(80.0)),
                height: Some(Dim::Points(24.0)),
                flex_direction: Some(FlexDir::Column),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            1,
            &Style {
                width: Some(Dim::Points(80.0)),
                height: Some(Dim::Points(12.0)),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            2,
            &Style {
                width: Some(Dim::Points(80.0)),
                height: Some(Dim::Points(12.0)),
                ..Default::default()
            },
        )
        .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();
        let r1 = e.computed(1).unwrap();
        let r2 = e.computed(2).unwrap();
        assert_eq!(
            r1,
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 12
            }
        );
        assert_eq!(
            r2,
            Rect {
                x: 0,
                y: 12,
                width: 80,
                height: 12
            }
        );
    }

    // ── E3. apply_style gap end-to-end ────────────────────────────────────────
    // Oracle case 3 (hand-derived): gap=2, two 10×5 children in a flex row.
    // Expected: c1.x=0, c2.x=12 (c1.width + gap = 10 + 2).
    #[test]
    fn apply_style_gap() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(0, 2, 1).unwrap();

        e.apply_style(
            0,
            &Style {
                width: Some(Dim::Points(80.0)),
                height: Some(Dim::Points(24.0)),
                gap: Some(2.0),
                align_items: Some(Align::FlexStart),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            1,
            &Style {
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(5.0)),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            2,
            &Style {
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(5.0)),
                ..Default::default()
            },
        )
        .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();
        let c1 = e.computed(1).unwrap();
        let c2 = e.computed(2).unwrap();
        assert_eq!(c1.x, 0);
        assert_eq!(c2.x, 12); // 10 (c1 width) + 2 (gap)
    }

    // ── E4. apply_style padding end-to-end ───────────────────────────────────
    // A root with padding=2 and two children: the first child starts at x=2, y=2.
    #[test]
    fn apply_style_padding() {
        let mut e = engine_with(&[0, 1]);
        e.insert_child(0, 1, 0).unwrap();

        e.apply_style(
            0,
            &Style {
                width: Some(Dim::Points(80.0)),
                height: Some(Dim::Points(24.0)),
                padding: Some(Lp::Points(2.0)),
                align_items: Some(Align::FlexStart),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            1,
            &Style {
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(5.0)),
                ..Default::default()
            },
        )
        .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();
        let child = e.computed(1).unwrap();
        assert_eq!(child.x, 2);
        assert_eq!(child.y, 2);
    }

    // ── E5. apply_style border end-to-end ────────────────────────────────────
    // Oracle case 2 (hand-derived): a 10×5 box with a full border (all 4 edges
    // = 1 cell).  The single child (6×3 explicit size) should start at x=1, y=1
    // (pushed inward by the 1-cell border on left and top).
    #[test]
    fn apply_style_border() {
        let mut e = engine_with(&[0, 1]);
        e.insert_child(0, 1, 0).unwrap();

        e.apply_style(
            0,
            &Style {
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(5.0)),
                border_style: Some(BorderStyle::Named("single".into())),
                align_items: Some(Align::FlexStart),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            1,
            &Style {
                width: Some(Dim::Points(6.0)),
                height: Some(Dim::Points(3.0)),
                ..Default::default()
            },
        )
        .unwrap();

        e.calculate(0, 10.0, Some(5.0)).unwrap();
        let child = e.computed(1).unwrap();
        // Border = 1 each side → content area origin at (1, 1).
        assert_eq!(child.x, 1);
        assert_eq!(child.y, 1);
    }

    // ── E6. computed_absolute on a nested-offset tree (#124, pin A1) ────────
    // Three levels with offsets at EVERY level (root padding, middle margin,
    // inner margin), hand-computed:
    //   root (id 0): padding 2                  → abs (0, 0)
    //   middle (id 1): margin-left 3, -top 2    → rel (2+3, 2+2) = (5, 4); abs (5, 4)
    //   inner (id 2): margin-left 4, -top 1     → rel (4, 1);              abs (9, 5)
    // Mutation guard: the inner node's absolute (9, 5) differs from its
    // parent-relative (4, 1) — an implementation returning relative coords
    // (the pre-#124 limitation) fails the abs assertions.
    #[test]
    fn computed_absolute_nested_offsets() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(1, 2, 0).unwrap();

        e.apply_style(
            0,
            &Style {
                width: Some(Dim::Points(40.0)),
                height: Some(Dim::Points(10.0)),
                padding: Some(Lp::Points(2.0)),
                align_items: Some(Align::FlexStart),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            1,
            &Style {
                width: Some(Dim::Points(20.0)),
                height: Some(Dim::Points(6.0)),
                margin_left: Some(Lp::Points(3.0)),
                margin_top: Some(Lp::Points(2.0)),
                align_items: Some(Align::FlexStart),
                ..Default::default()
            },
        )
        .unwrap();
        e.apply_style(
            2,
            &Style {
                width: Some(Dim::Points(6.0)),
                height: Some(Dim::Points(2.0)),
                margin_left: Some(Lp::Points(4.0)),
                margin_top: Some(Lp::Points(1.0)),
                ..Default::default()
            },
        )
        .unwrap();

        e.calculate(0, 40.0, Some(10.0)).unwrap();

        // Parent-relative truths (unchanged contract — `computed` stays relative).
        assert_eq!(
            e.computed(1).unwrap(),
            Rect {
                x: 5,
                y: 4,
                width: 20,
                height: 6
            }
        );
        assert_eq!(
            e.computed(2).unwrap(),
            Rect {
                x: 4,
                y: 1,
                width: 6,
                height: 2
            }
        );

        // Absolute rects: root at origin; nested offsets ACCUMULATE.
        assert_eq!(
            e.computed_absolute(0).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 40,
                height: 10
            }
        );
        assert_eq!(
            e.computed_absolute(1).unwrap(),
            Rect {
                x: 5,
                y: 4,
                width: 20,
                height: 6
            }
        );
        assert_eq!(
            e.computed_absolute(2).unwrap(),
            Rect {
                x: 9,
                y: 5,
                width: 6,
                height: 2
            }
        );

        // Discrimination: absolute ≠ relative for the doubly-nested node.
        assert_ne!(e.computed_absolute(2), e.computed(2));

        // Unknown id → None (no fallback; see `computed_absolute` docs).
        assert_eq!(e.computed_absolute(99), None);
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // Pre-existing layout tests (kept; bypass apply_style for direct coverage)
    // ═══════════════════════════════════════════════════════════════════════════

    // ── 1. Single root sized to the viewport ────────────────────────────────
    // The root node has an explicit 80×24 size; after calculate its rect must
    // exactly match the viewport.
    #[test]
    fn single_root_fills_viewport() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();

        let nid = e.id_map[&0];
        e.tree
            .set_style(
                nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();

        let r = e.computed(0).unwrap();
        assert_eq!(
            r,
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 24
            }
        );
    }

    // ── 2. Root + two default-style children ────────────────────────────────
    // Default style: display:flex, flex-direction:row (taffy default).
    // Give the children explicit widths (10 and 20) that sum well under the
    // 80-column root so flex-shrink does not compress them.  The key assertion
    // is `c2.x == c1.width`, which pins the row-advance that proves
    // flex-direction:row is the default.
    #[test]
    fn root_two_default_children() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(0, 2, 1).unwrap();

        let root_nid = e.id_map[&0];
        let c1_nid = e.id_map[&1];
        let c2_nid = e.id_map[&2];
        e.tree
            .set_style(
                root_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();
        e.tree
            .set_style(
                c1_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(10.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();
        e.tree
            .set_style(
                c2_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(20.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();

        assert_eq!(
            e.computed(0).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 24
            }
        );

        let c1 = e.computed(1).unwrap();
        let c2 = e.computed(2).unwrap();
        assert_eq!(c1.x, 0);
        assert_eq!(c1.y, 0);
        assert_eq!(c2.y, 0); // flex-direction:row → both on same row
        assert_eq!(c1.width, 10);
        assert_eq!(c2.width, 20);
        assert_eq!(c2.x, c1.x + i32::from(c1.width));
    }

    // ── 3. Nested box ────────────────────────────────────────────────────────
    // root(80×24) → outer(40×24) → inner(20×24)
    #[test]
    fn nested_box() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(1, 2, 0).unwrap();

        let root_nid = e.id_map[&0];
        let outer_nid = e.id_map[&1];
        let inner_nid = e.id_map[&2];

        e.tree
            .set_style(
                root_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();
        e.tree
            .set_style(
                outer_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(40.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();
        e.tree
            .set_style(
                inner_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(20.0),
                        height: pt(24.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();

        assert_eq!(
            e.computed(0).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 24
            }
        );
        assert_eq!(
            e.computed(1).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 40,
                height: 24
            }
        );
        assert_eq!(
            e.computed(2).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 20,
                height: 24
            }
        );
    }

    // ── 4. Recalculate after apply_style ─────────────────────────────────────
    // Resize root from 80×24 to 40×12 via apply_style, then recalculate.
    #[test]
    fn recalculate_after_style_change() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();

        let initial = Style {
            width: Some(Dim::Points(80.0)),
            height: Some(Dim::Points(24.0)),
            ..Default::default()
        };
        e.apply_style(0, &initial).unwrap();
        e.calculate(0, 80.0, Some(24.0)).unwrap();
        assert_eq!(
            e.computed(0).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 24
            }
        );

        // Resize via apply_style (mark_dirty is implicit in set_style).
        let resized = Style {
            width: Some(Dim::Points(40.0)),
            height: Some(Dim::Points(12.0)),
            ..Default::default()
        };
        e.apply_style(0, &resized).unwrap();
        e.mark_dirty(0).unwrap();
        e.calculate(0, 40.0, Some(12.0)).unwrap();
        assert_eq!(
            e.computed(0).unwrap(),
            Rect {
                x: 0,
                y: 0,
                width: 40,
                height: 12
            }
        );
    }

    // ── 5. computed() on unknown id returns None, not a panic ─────────────────
    #[test]
    fn computed_unknown_id_returns_none() {
        let e = TaffyEngine::new();
        assert_eq!(e.computed(999), None);
    }

    // ── 6. create duplicate id is a no-op ────────────────────────────────────
    #[test]
    fn create_duplicate_is_noop() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();
        let nid_first = e.id_map[&0];
        e.create(0).unwrap();
        assert_eq!(e.id_map[&0], nid_first);
    }

    // ── 7. measure function is called for leaf nodes ──────────────────────────
    #[test]
    fn measure_fn_is_invoked() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();
        e.create(1).unwrap();

        let root_nid = e.id_map[&0];
        e.tree
            .set_style(
                root_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(24.0),
                    },
                    align_items: Some(AlignItems::FlexStart),
                    ..Default::default()
                },
            )
            .unwrap();

        e.insert_child(0, 1, 0).unwrap();

        e.set_measure(
            1,
            Box::new(|_known, _avail| Size {
                width: 10.0,
                height: 3.0,
            }),
        );

        e.calculate(0, 80.0, Some(24.0)).unwrap();

        let leaf = e.computed(1).unwrap();
        assert_eq!(leaf.width, 10);
        assert_eq!(leaf.height, 3);
    }

    // ── 8. insert_child index clamping ───────────────────────────────────────
    #[test]
    fn insert_child_index_clamp_appends() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(0, 2, 9999).unwrap();

        let root_nid = e.id_map[&0];
        let root_nid_children = e.tree.children(root_nid).unwrap();
        assert_eq!(root_nid_children, vec![e.id_map[&1], e.id_map[&2]]);
    }

    // ── destroy: node lifecycle ───────────────────────────────────────────────

    // destroy removes the node from the engine; computed() returns None after.
    // Also verifies that a registered measure function is dropped on destroy.
    #[test]
    fn destroy_removes_node() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();
        e.create(1).unwrap();
        e.set_measure(
            1,
            Box::new(|_, _| Size {
                width: 5.0,
                height: 1.0,
            }),
        );
        // Pre-calculate: computed() falls back to the live taffy layout.
        assert!(e.computed(1).is_some());

        // Post-calculate: node 1 is inserted under root 0, calculate() fills
        // self.rounded.  After destroy(1), computed() must return None — not the
        // stale rounded rect (the bug self.rounded.remove(&id) fixes).
        e.insert_child(0, 1, 0).unwrap();
        let root_s = crate::dom::Style {
            width: Some(crate::dom::Dim::Points(80.0)),
            height: Some(crate::dom::Dim::Points(24.0)),
            ..Default::default()
        };
        e.apply_style(0, &root_s).unwrap();
        e.calculate(0, 80.0, Some(24.0)).unwrap();
        // Now served from self.rounded (not the fallback path).
        assert!(e.computed(1).is_some());

        e.destroy(1);
        assert!(e.computed(1).is_none());
        // id_map and measures entries must also be gone (no dangling state).
        assert!(!e.id_map.contains_key(&1));
        assert!(!e.measures.contains_key(&1));
    }

    // destroy on unknown id is a silent no-op — matches ink's guard-style
    // error philosophy (no panic, no change to other nodes).
    #[test]
    fn destroy_unknown_id_is_noop() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();
        e.destroy(999); // must not panic
        assert!(e.computed(0).is_some());
    }

    // destroy cleans up state so re-create + new measure works cleanly.
    // Validates the invalidation contract: after destroy, a fresh node at the
    // same id has no stale measure function from the previous occupant.
    #[test]
    fn destroy_then_recreate_clean_state() {
        let mut e = TaffyEngine::new();
        e.create(0).unwrap();
        e.create(1).unwrap();
        e.insert_child(0, 1, 0).unwrap();

        let root_s = crate::dom::Style {
            width: Some(crate::dom::Dim::Points(80.0)),
            height: Some(crate::dom::Dim::Points(24.0)),
            align_items: Some(crate::dom::Align::FlexStart),
            ..Default::default()
        };
        e.apply_style(0, &root_s).unwrap();
        e.set_measure(
            1,
            Box::new(|_, _| Size {
                width: 5.0,
                height: 1.0,
            }),
        );
        e.calculate(0, 80.0, Some(24.0)).unwrap();
        assert_eq!(e.computed(1).unwrap().width, 5);

        e.destroy(1);
        e.destroy(0);

        // Re-create with different measure — must not inherit old closure.
        e.create(0).unwrap();
        e.create(1).unwrap();
        e.insert_child(0, 1, 0).unwrap();
        e.apply_style(0, &root_s).unwrap();
        e.set_measure(
            1,
            Box::new(|_, _| Size {
                width: 7.0,
                height: 1.0,
            }),
        );
        e.calculate(0, 80.0, Some(24.0)).unwrap();
        assert_eq!(e.computed(1).unwrap().width, 7);
    }

    // ── 9. remove_child detaches without destroying node ─────────────────────
    #[test]
    fn remove_child_detaches() {
        let mut e = engine_with(&[0, 1]);
        e.insert_child(0, 1, 0).unwrap();
        e.remove_child(0, 1).unwrap();

        assert!(e.id_map.contains_key(&1));
        let root_nid = e.id_map[&0];
        assert_eq!(e.tree.child_count(root_nid), 0);
    }

    // ── 10. flex column layout ────────────────────────────────────────────────
    #[test]
    fn flex_column_two_children() {
        let mut e = engine_with(&[0, 1, 2]);
        e.insert_child(0, 1, 0).unwrap();
        e.insert_child(0, 2, 1).unwrap();

        let root_nid = e.id_map[&0];
        let c1_nid = e.id_map[&1];
        let c2_nid = e.id_map[&2];

        e.tree
            .set_style(
                root_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(24.0),
                    },
                    flex_direction: TFD::Column,
                    ..Default::default()
                },
            )
            .unwrap();
        e.tree
            .set_style(
                c1_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(12.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();
        e.tree
            .set_style(
                c2_nid,
                TaffyStyle {
                    size: taffy::geometry::Size {
                        width: pt(80.0),
                        height: pt(12.0),
                    },
                    ..Default::default()
                },
            )
            .unwrap();

        e.calculate(0, 80.0, Some(24.0)).unwrap();

        let r1 = e.computed(1).unwrap();
        let r2 = e.computed(2).unwrap();

        assert_eq!(
            r1,
            Rect {
                x: 0,
                y: 0,
                width: 80,
                height: 12
            }
        );
        assert_eq!(
            r2,
            Rect {
                x: 0,
                y: 12,
                width: 80,
                height: 12
            }
        );
    }

    // ═══════════════════════════════════════════════════════════════════════════
    // round_value_to_pixel_grid kernel — full branch-matrix unit tests
    //
    // Each case is hand-derived from the branch order in the source (lines
    // 443-458 at the time of writing).  Branch order matters; the most critical
    // invariant is that the fractial≈1 ceil fires BEFORE the force_floor guard.
    // ═══════════════════════════════════════════════════════════════════════════

    // (1) fractial ≈ 0 within epsilon (e.g. 5.00005) → floor to whole number
    // regardless of force flags (branch 1 fires first).
    #[test]
    fn kernel_fractional_near_zero_floors_to_whole() {
        // 5.00005 % 1.0 = 0.00005; inexact_equals(0.00005, 0.0) = true (< 0.0001)
        assert_eq!(round_value_to_pixel_grid(5.00005, false, false), 5.0);
        // force_ceil=true must not override branch 1
        assert_eq!(round_value_to_pixel_grid(5.00005, true, false), 5.0);
        // force_floor=true must not override branch 1
        assert_eq!(round_value_to_pixel_grid(5.00005, false, true), 5.0);
    }

    // (2) fractial ≈ 1 within epsilon (e.g. 4.99995) → ceil to whole number.
    // CRITICAL: this branch fires BEFORE force_floor, so even force_floor=true
    // must produce 5.0 (not 4.0).  This is the ordering the review most wants
    // guarded.
    #[test]
    fn kernel_fractional_near_one_ceils_before_force_floor() {
        // 4.99995 % 1.0 = 0.99995; inexact_equals(0.99995, 1.0) = true
        assert_eq!(round_value_to_pixel_grid(4.99995, false, false), 5.0);
        // force_floor=true must NOT override: branch 2 wins over branch 3
        assert_eq!(round_value_to_pixel_grid(4.99995, false, true), 5.0);
    }

    // (3) force_ceil with mid-fractional value → ceil.
    #[test]
    fn kernel_force_ceil_rounds_up() {
        // 4.3 % 1.0 = 0.3; not near 0/1; force_ceil=true → branch 2/3 → 5.0
        assert_eq!(round_value_to_pixel_grid(4.3, true, false), 5.0);
    }

    // (4) force_floor with mid-fractional value → floor.
    #[test]
    fn kernel_force_floor_rounds_down() {
        // 4.7 % 1.0 = 0.7; not near 0/1; force_floor=true → branch 3 → 4.0
        assert_eq!(round_value_to_pixel_grid(4.7, false, true), 4.0);
    }

    // (5) round-half-up: ties go toward +inf.
    #[test]
    fn kernel_round_half_up_tie() {
        // 4.5: fractial=0.5; inexact_equals(0.5, 0.5)=true → branch 4 → 5.0
        assert_eq!(round_value_to_pixel_grid(4.5, false, false), 5.0);
        // 4.49: fractial=0.49; not near 0/1; 0.49<0.5; inexact(0.49,0.5)=false → branch 5 → 4.0
        assert_eq!(round_value_to_pixel_grid(4.49, false, false), 4.0);
        // 4.51: fractial=0.51; 0.51>0.5 → branch 4 → 5.0
        assert_eq!(round_value_to_pixel_grid(4.51, false, false), 5.0);
    }

    // (5b) exact 0.5 tie via inexact_equals: 4.49995 → 5.0.
    // fractial=0.49995; inexact_equals(0.49995, 0.5) = |−0.00005| < 0.0001 = true → branch 4
    #[test]
    fn kernel_half_epsilon_tie_ceils() {
        assert_eq!(round_value_to_pixel_grid(4.49995, false, false), 5.0);
    }

    // (6) Negative values: the fractial<0 correction (+=1.0) normalises fmod
    // output into [0,1) before the branch tree.
    #[test]
    fn kernel_negative_values() {
        // -4.5 % 1.0 = -0.5 → +1.0 → 0.5; inexact(0.5,0.5)=true → branch 4 → -4.5+0.5 = -4.0
        assert_eq!(round_value_to_pixel_grid(-4.5, false, false), -4.0);
        // -4.3 % 1.0 = -0.3 → +1.0 → 0.7; 0.7>0.5 → branch 4 → -4.3+0.3 = -4.0
        assert_eq!(round_value_to_pixel_grid(-4.3, false, false), -4.0);
        // -4.7 % 1.0 = -0.7 → +1.0 → 0.3; 0.3<0.5; inexact(0.3,0.5)=false → branch 5 → -4.7-0.3 = -5.0
        assert_eq!(round_value_to_pixel_grid(-4.7, false, false), -5.0);
    }

    // ── inexact_equals boundary ───────────────────────────────────────────────
    // The operator is strict `<` (yoga/Comparison.h, mirrored at line 405).
    // |a−b| == 0.0001 exactly is NOT equal; just under is equal.

    #[test]
    fn inexact_equals_at_threshold_is_not_equal() {
        // |0.0001 − 0.0| = 0.0001; 0.0001 < 0.0001 is false
        assert!(!inexact_equals(0.0001, 0.0));
    }

    #[test]
    fn inexact_equals_just_under_threshold_is_equal() {
        // |0.00009 − 0.0| = 0.00009 < 0.0001 → true
        assert!(inexact_equals(0.00009, 0.0));
    }
}