inkferro-core 0.1.0

//! Plain-frame render assembly — M1-5 implementation per ADR-2.
//!
//! # Module structure
//! - `cli_boxes`  — vendored cli-boxes@4.0.1 char table (border drawing chars).
//! - `grid`       — char grid: write/clip/wide-char cleanup/get (output.ts port).
//! - `border`     — border char drawing (render-border.ts port, plain slice).
//! - `walk`       — arena tree walk → grid (render-node-to-output.ts port).
//! - `mod` (this) — `render_to_string` entry point tying layout + grid together.
//!
//! # Engine-per-call design (ADR-3, M3-A)
//! Both `render_to_string` and the `build_layout_engine` seam create a **fresh**
//! `TaffyEngine` on each call. ADR-3 (`docs/adr3-engine-lifetime.md`) chose
//! per-frame rebuild over a live incremental engine: persistence lives in the
//! `Arena` (which `InkRoot` will own across `commit()` calls, M3-D), while the
//! engine is a pure function of the arena at render time. A fresh engine
//! re-runs `set_measure` for every text node every frame, so the
//! measure-invalidation discipline (`layout/engine.rs:78-82`) is satisfied for
//! free — the rejected incremental option would have had to replicate it by
//! hand, at the risk of silent text-measure corruption. The node-creation walk
//! is NEVER re-run against an already-populated engine: `insert_child` appends,
//! so reuse would duplicate child lists. See ADR-3 for the full rationale.
//!
//! # Height for unconstrained render (render-to-string.ts:62-68 citation)
//! ink's `renderToString` calls:
//! ```ts
//! rootNode.yogaNode!.calculateLayout(undefined, undefined, Yoga.DIRECTION_LTR);
//! ```
//! ink passes `undefined` for both axes in yoga, but the root node has an
//! explicit `setWidth(columns)` call immediately before (render-to-string.ts:62),
//! so in practice width is definite and only height is unconstrained.
//! `render_to_string` mirrors this: width is `AvailableSpace::Definite(columns)`,
//! height is `AvailableSpace::MaxContent` (passed as `None` to `calculate`).
//! The grid is sized to the computed root height so trailing empty rows are
//! never included in the output.

pub mod background;
pub mod border;
pub mod cli_boxes;
pub mod colorize;
#[cfg(test)]
mod colorize_chalk_parity_tests;
pub mod grid;
pub mod walk;

pub use colorize::{ColorLevel, Kind as ColorKind, colorize, dim};

use crate::dom::{Arena, Kind};
use crate::layout::{LayoutEngine, Rect, TaffyEngine};
use crate::render::grid::Grid;
use crate::render::walk::{TransformAccessor, walk, walk_static};
use crate::text_measure::build_measure_fn_for;

/// Render the arena tree rooted at `root_id` to a plain-frame string.
///
/// Orchestration (mirrors `renderer.ts` + `render-to-string.ts`):
/// 1. Build a fresh `TaffyEngine` (engine-per-call; see module docs).
/// 2. Walk the arena: create taffy nodes, apply styles, set text measures.
/// 3. `calculate(root, width, MAX_HEIGHT)` — unconstrained height per ink.
/// 4. Walk arena again: render each node into a `Grid`.
/// 5. Return `grid.get().0` (the trimmed frame string).
///
/// The returned string matches ink's `renderToString` output for unstyled
/// content (no SGR transformers, no static nodes).
pub fn render_to_string(arena: &Arena, root_id: u32, width: u16) -> String {
    // render_to_string is the PLAIN slice of `render_styled`: a no-op transform
    // accessor (`&|_| None`) leaves the transformer chain empty at every node,
    // so the styled write path degenerates to the plain one and the bytes are
    // identical to the pre-seam output (the corpus, 188/5 exact, is the proof).
    // The returned height is discarded here; callers that need it use
    // `render_styled` directly.
    //
    // Color level is fixed to `Truecolor` (=3) here: this helper backs the
    // `layout_corpus` byte tests, whose border-color EXPECTED literals are
    // chalk@5 level-3 bytes. The PRODUCTION `renderToString` does NOT go through
    // this helper — it calls `render_frame` (napi) with the detected
    // `opts.color_level`, so honoring the level lives there, not here.
    render_styled(arena, root_id, width, &|_| None, ColorLevel::Truecolor).0
}

/// Render the arena tree rooted at `root_id` to a **styled** frame, returning
/// both the frame string and its height in rows (`mirrors ink's `{output,
/// height}`, output.ts:315-316). This is the entry M3-E `render_frame` calls.
///
/// `transform_of` is the per-node own-transform seam (see
/// [`walk::TransformAccessor`]): given a dom id it returns the node's own output
/// transform (ink's `internal_transform`), or `None`. `<Text color>` SGR is *not*
/// a separate path — in ink it lives **inside** `internal_transform`
/// (Text.tsx:94-130 → `colorize`), so a core caller wires `colorize` into the
/// accessor and napi (M3-E) dispatches to a JS `internal_transform`; both flow
/// through the same `[own, ...inherited]` chain (render-node-to-output.ts:136).
///
/// Reuses [`build_layout_engine`] (the M3-A seam) verbatim — the layout build is
/// never duplicated. An empty/zero-sized frame returns `(String::new(), 0)`,
/// matching the prior `render_to_string` error/empty path.
pub fn render_styled<'a>(
    arena: &'a Arena,
    root_id: u32,
    width: u16,
    transform_of: &'a TransformAccessor<'a>,
    color_level: ColorLevel,
) -> (String, u16) {
    // ── 1. Layout pass (ADR-3 seam) ───────────────────────────────────────────
    // Build a fresh engine + compute layout via the shared seam. `InkRoot`
    // (M3-D) calls the same seam each frame; this entry is the styled wrapper
    // over it, so the two paths cannot drift in their layout.
    let Some((engine, root_rect)) = build_layout_engine(arena, root_id, width) else {
        return (String::new(), 0);
    };

    // ── 2. Render pass ────────────────────────────────────────────────────────
    // renderer.ts:37-39: Output is sized to the computed root dimensions.
    let grid_rows = root_rect.height as usize;
    let grid_cols = root_rect.width as usize;

    if grid_rows == 0 || grid_cols == 0 {
        return (String::new(), 0);
    }

    let mut grid = Grid::new(grid_rows, grid_cols);

    // Build a rect accessor closure from the engine.
    // The closure captures engine by reference for the walk.
    let rect_fn = |id: u32| engine.computed(id);

    walk(
        arena,
        root_id,
        &rect_fn,
        transform_of,
        &mut grid,
        color_level,
    );

    // grid.get() returns (output, height); height == grid_rows == root height.
    let (output, height) = grid.get();
    (output, height as u16)
}

/// Render the **static** subtree (ink's `<Static>`) to its standalone output
/// string — the text ink prints once, above the live region.
///
/// This is the SECOND render pass, a faithful port of `renderer.ts`'s static
/// branch (renderer.ts:46-66):
/// ```ts
/// let staticOutput;
/// if (node.staticNode?.yogaNode) {
///   staticOutput = new Output({
///     width:  node.staticNode.yogaNode.getComputedWidth(),
///     height: node.staticNode.yogaNode.getComputedHeight(),
///   });
///   renderNodeToOutput(node.staticNode, staticOutput, {skipStaticElements: false});
/// }
/// // …
/// staticOutput: staticOutput ? `${staticOutput.get().output}\n` : '',
/// ```
///
/// Semantics, point by point:
/// 1. **Find the static node.** ink tracks a single `node.staticNode` set by the
///    reconciler when `internal_static` is applied (reconciler.ts:236-244). The
///    arena instead marks the node with `is_static` (set by `Op::SetStatic`), so
///    we DFS from `root_id` for the first `is_static` node. No static node →
///    return `""` (the common case; matches `staticNode` being `undefined`).
/// 2. **Layout.** Reuse [`build_layout_engine`] at the SAME `width` ink lays the
///    root out at — the static node is part of that one tree, so its computed
///    rect (`engine.computed(static_id)`) falls out of the single root layout,
///    exactly as `node.staticNode.yogaNode` is laid out by the root's
///    `calculateLayout`. If the static id has no computed rect, return `""`
///    (matches `node.staticNode?.yogaNode` being absent).
/// 3. **Own-sized grid.** Size the static grid to the static node's OWN computed
///    width/height (renderer.ts:50-52: `new Output({width: …getComputedWidth(),
///    height: …getComputedHeight()})`), NOT the root's.
/// 4. **Walk at offset 0** via [`walk_static`] (`skipStaticElements: false`): the
///    static entry's own computed left/top become the first write position
///    (render-node-to-output.ts:129-130 with offsetX/Y defaulting to 0).
/// 5. **Trailing newline** (renderer.ts:64-66): a PRESENT static node always
///    appends `\n` ("static output doesn't have one, so interactive output will
///    override last line of static output"), even for an empty body (→ `"\n"`).
///    An ABSENT static node yields `""`. A zero-dimensioned static node skips
///    `Grid::new` and still yields `"\n"`, matching `staticOutput.get().output`
///    being `""` for an empty `Output` plus the appended newline.
///
/// `transform_of` is the same per-node own-transform seam [`render_styled`] uses;
/// the napi caller passes the SAME accessor so a `<Transform>`/`<Text color>`
/// inside `<Static>` is honored in the static pass too.
pub fn render_static<'a>(
    arena: &'a Arena,
    root_id: u32,
    width: u16,
    transform_of: &'a TransformAccessor<'a>,
    color_level: ColorLevel,
) -> String {
    // ── 1. Find the static node (DFS from root) — short-circuit BEFORE any
    //       layout build so a static-free frame (the common case) skips the
    //       layout/grid/walk work below. It still pays one O(n) pre-order DFS of
    //       the arena (`find_static_node`) per frame before it can return `""`;
    //       negligible in practice, but not free.
    let Some(static_id) = find_static_node(arena, root_id) else {
        return String::new();
    };

    // ── 2. Layout pass: the static node is part of the one root layout, so its
    //       computed rect falls out of a `build_layout_engine` build at the SAME
    //       width ink uses. NOTE: this builds a FRESH taffy tree rather than
    //       reusing the M3-A persistent engine, so a static-bearing frame computes
    //       layout twice (main pass + here). Perf-only, and only on the rare
    //       static-bearing frame; correctness is unaffected.
    let Some((engine, _root_rect)) = build_layout_engine(arena, root_id, width) else {
        return String::new();
    };
    let Some(static_rect) = engine.computed(static_id) else {
        return String::new();
    };

    // ── 3. Own-sized grid (renderer.ts:50-52). A zero-dim static node still gets
    //       the trailing newline below (a present `staticNode` always does).
    let grid_rows = static_rect.height as usize;
    let grid_cols = static_rect.width as usize;
    if grid_rows == 0 || grid_cols == 0 {
        return "\n".to_owned();
    }

    let mut grid = Grid::new(grid_rows, grid_cols);
    let rect_fn = |id: u32| engine.computed(id);

    // ── 4. Render pass with skipStaticElements=false (renderer.ts:54).
    walk_static(
        arena,
        static_id,
        &rect_fn,
        transform_of,
        &mut grid,
        color_level,
    );

    // ── 5. Trailing newline (renderer.ts:64-66): present static → body + "\n".
    let (body, _height) = grid.get();
    format!("{body}\n")
}

/// DFS the arena tree rooted at `root_id` for the first `is_static` node, in
/// pre-order. ink supports exactly ONE `<Static>` per tree (the reconciler keeps
/// a lone `rootNode.staticNode` reference, reconciler.ts:243), so in every
/// supported tree there is at most one `is_static` node and "first in pre-order"
/// is unambiguous — matching ink's single `node.staticNode`.
///
/// Multiple static nodes are undefined in ink itself. NOTE: for that
/// ink-undefined case the selection *direction* differs: we take the FIRST
/// `is_static` node in pre-order, whereas ink's reconciler reassigns
/// `rootNode.staticNode = node` on every `internal_static` apply
/// (reconciler.ts:243), so ink's effective static node is the LAST one committed.
/// Both pick deterministically; they only diverge on a tree ink does not support.
/// Returns the static entry id, or `None` when the tree carries no static node.
fn find_static_node(arena: &Arena, id: u32) -> Option<u32> {
    let node = arena.get(id)?;
    if node.is_static {
        return Some(id);
    }
    for &child_id in &node.children {
        if let Some(found) = find_static_node(arena, child_id) {
            return Some(found);
        }
    }
    None
}

/// Build a fresh layout engine for the arena tree rooted at `root_id`, compute
/// layout at the given `width`, and return the built engine plus the root rect.
///
/// This is the **M3-A engine-lifetime seam** (ADR-3,
/// `docs/adr3-engine-lifetime.md`) — the **public** entry `InkRoot`
/// (`inkferro-napi`, M3-D) calls each `render_frame`. `render_to_string` calls
/// it as step 1 of its own body, so the two paths cannot drift. It is the single
/// place the taffy tree is constructed, so callers cannot accidentally re-run
/// node creation against a populated engine (which would duplicate child lists —
/// `insert_child` appends).
///
/// It is `pub` (not `pub(crate)`) because the consumer lives in a *different*
/// crate (`inkferro-napi`). Returning the concrete `TaffyEngine` — rather than
/// `impl LayoutEngine` — lets `InkRoot` store it as a named field and read
/// `computed(id)` later (still via the `LayoutEngine` trait). This deliberately
/// names the concrete backend across the napi boundary; the ADR-1
/// `LayoutEngine`-trait seam still governs *behavior*, and a backend swap would
/// change only this return type in one place.
///
/// Returns the **built-and-computed** engine so a single per-frame build serves
/// both the render walk (M3-E reads `engine.computed(id)` as the rect accessor)
/// and `measure(id)` (M3-F reads `engine.computed(id)` from the *same* stored
/// build) — no second rebuild.
///
/// # Per-frame rebuild (ADR-3 Option A)
/// Always allocates a fresh `TaffyEngine`. Persistence is the `Arena`'s job; the
/// engine is a pure function of the arena at render time. A fresh engine
/// re-`set_measure`s every text node, satisfying the measure-invalidation
/// discipline (`layout/engine.rs:78-82`) for free.
///
/// Returns `None` if `calculate` fails (e.g. an inconsistent tree); the caller
/// renders an empty frame, matching the prior `render_to_string` error path.
pub fn build_layout_engine(arena: &Arena, root_id: u32, width: u16) -> Option<(TaffyEngine, Rect)> {
    let mut engine = TaffyEngine::new();

    // First pass: create nodes and wire the tree. Run on a FRESH engine only —
    // see ADR-3 "the trap inside A": re-running this against a populated engine
    // re-appends children and corrupts the layout.
    create_layout_nodes(arena, root_id, &mut engine);

    // Width is definite (caller-supplied columns). Height is unconstrained —
    // mirrors ink's render-to-string.ts:62-68 where yogaNode.calculateLayout
    // receives `undefined` for height (MaxContent), letting content determine
    // the frame height. None → AvailableSpace::MaxContent in TaffyEngine::calculate.
    if engine.calculate(root_id, width as f32, None).is_err() {
        return None;
    }

    // Read the computed root rect to size the grid (renderer.ts:37-39). Fall
    // back to a zero-height rect at the caller width if the root id is unknown
    // — preserves the prior `unwrap_or` behavior so empty/absent roots render
    // an empty frame rather than panicking.
    let root_rect = engine.computed(root_id).unwrap_or(Rect {
        x: 0,
        y: 0,
        width,
        height: 0,
    });

    Some((engine, root_rect))
}

/// Recursively register all arena nodes into the layout engine.
///
/// For each node: create the taffy node, apply its style, attach text measure
/// for Text/VirtualText nodes, then insert children in order.
fn create_layout_nodes(arena: &Arena, id: u32, engine: &mut TaffyEngine) {
    let Some(node) = arena.get(id) else { return };

    // Create the taffy node (idempotent).
    let _ = engine.create(id);

    let style = match node.kind {
        Kind::Root => root_style_with_ink_defaults(&node.style),
        _ => node.style.clone(),
    };
    let _ = engine.apply_style(id, &style);

    // Wire text measure for text-bearing nodes, then STOP: a Text/VirtualText node
    // is a taffy LEAF whose measure fn squashes its WHOLE subtree once
    // (`build_measure_fn_for` → `squash_text`), exactly like ink's `ink-text`
    // (dom.ts:222-246) — whose nested `ink-virtual-text` children carry NO yoga node
    // (dom.ts:102) and are never inserted as yoga children (dom.ts:125). #71: NOT
    // returning here gave every nested segment its own taffy node + measure fn, so
    // taffy (which only measures LEAF nodes) measured each inner segment ALONE in
    // its own wrap mode — truncating/wrapping per leaf instead of over the combined
    // squash. Returning makes the text-root the sole measured unit → squash-then-
    // truncate, byte-identical to ink and to the render walk (which already squashes
    // the whole Text subtree once, walk.rs Text arm). The reconciler forbids a Box
    // child of a Text node (`caseBoxInTextThrows`), so a Text node never has
    // layout-bearing children to recurse into; multi-segment text is purely nested
    // Text/VirtualText, all folded by `squash_text`. (Sibling Texts under a Box are
    // separate text-ROOTS, reached from the Box/Root branch below — unaffected; and
    // when nothing truncates, the squashed width equals the sum of segment widths,
    // so single-segment text, fitting multi-segment text, the layout corpus, and the
    // zero-flicker goldens keep identical dimensions.)
    if matches!(node.kind, Kind::Text | Kind::VirtualText) {
        engine.set_measure(id, build_measure_fn_for(arena, id));
        return;
    }

    // Clone children list to avoid borrow conflict during recursion.
    let children: Vec<u32> = node.children.clone();
    for (idx, &child_id) in children.iter().enumerate() {
        create_layout_nodes(arena, child_id, engine);
        let _ = engine.insert_child(id, child_id, idx);
    }
}

// ink's `ink-root` yoga node never receives Box styles — it
// relies on Yoga's intrinsic node defaults (flex-direction: column,
// align-items: stretch), which make every top-level child stretch to the
// full root width (dom.ts:95-105 createNode: bare Yoga.Node.create(),
// empty style). Taffy's default is flex-direction: row, so the Root
// must be column + stretch explicitly to reproduce ink-root.
// Box.tsx:85 forces flex-direction: row on every <Box>, so this is
// Root-only. The other half of ink-root identity — the root width pin
// (setWidth(columns)) — lives in TaffyEngine::calculate, which has the
// viewport_width parameter.
fn root_style_with_ink_defaults(s: &crate::dom::Style) -> crate::dom::Style {
    let mut style = s.clone();
    if style.flex_direction.is_none() {
        style.flex_direction = Some(crate::dom::FlexDir::Column);
    }
    if style.align_items.is_none() {
        style.align_items = Some(crate::dom::Align::Stretch);
    }
    style
}

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

#[cfg(test)]
mod tests {
    use super::*;
    use crate::dom::{Arena, BorderStyle, Dim, Display, Kind, Lp, Node, Overflow, Style, TextWrap};

    // ── helpers ──────────────────────────────────────────────────────────────

    fn make_root(arena: &mut Arena, id: u32) {
        arena.insert(id, Node::new(Kind::Root));
    }

    fn make_box(arena: &mut Arena, id: u32, style: Style) {
        let mut n = Node::new(Kind::Box);
        n.style = style;
        arena.insert(id, n);
    }

    fn make_text(arena: &mut Arena, id: u32, text: &str) {
        let mut n = Node::new(Kind::Text);
        n.text = Some(text.to_owned());
        arena.insert(id, n);
    }

    fn make_text_styled(arena: &mut Arena, id: u32, text: &str, style: Style) {
        let mut n = Node::new(Kind::Text);
        n.text = Some(text.to_owned());
        n.style = style;
        arena.insert(id, n);
    }

    fn add_child(arena: &mut Arena, parent: u32, child: u32) {
        arena.get_mut(parent).unwrap().children.push(child);
    }

    // ── E1: plain text at root (ink oracle) ─────────────────────────────────
    // ink: renderToString(<Text>Hello</Text>) === "Hello"
    #[test]
    fn e1_plain_text() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, "Hello");
        add_child(&mut a, 0, 1);
        assert_eq!(render_to_string(&a, 0, 80), "Hello");
    }

    // ── E2: single border, empty box (ink oracle) ────────────────────────────
    // ink: renderToString(<Box borderStyle="single" width={10} height={3}/>) ===
    //   "┌────────┐\n│        │\n└────────┘"
    #[test]
    fn e2_single_border_empty_10x3() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(3.0)),
                ..Style::default()
            },
        );
        add_child(&mut a, 0, 1);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "┌────────┐\n│        │\n└────────┘"
        );
    }

    // ── E3: border with text inside (ink oracle) ─────────────────────────────
    // ink: renderToString(<Box borderStyle="single" width={12} height={4}><Text>Hi</Text></Box>) ===
    //   "┌──────────┐\n│Hi        │\n│          │\n└──────────┘"
    #[test]
    fn e3_border_with_text() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                width: Some(Dim::Points(12.0)),
                height: Some(Dim::Points(4.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Hi");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "┌──────────┐\n│Hi        │\n│          │\n└──────────┘"
        );
    }

    // ── E4: column layout, two boxes (ink oracle) ────────────────────────────
    // ink: renderToString(
    //   <Box flexDirection="column" width={10}>
    //     <Box borderStyle="single"><Text>A</Text></Box>
    //     <Box borderStyle="single"><Text>B</Text></Box>
    //   </Box>) ===
    //   "┌────────┐\n│A       │\n└────────┘\n┌────────┐\n│B       │\n└────────┘"
    #[test]
    fn e4_column_two_bordered_boxes() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                flex_direction: Some(crate::dom::FlexDir::Column),
                width: Some(Dim::Points(10.0)),
                ..Style::default()
            },
        );
        make_box(
            &mut a,
            2,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                ..Style::default()
            },
        );
        make_text(&mut a, 3, "A");
        make_box(
            &mut a,
            4,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                ..Style::default()
            },
        );
        make_text(&mut a, 5, "B");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 2, 3);
        add_child(&mut a, 1, 4);
        add_child(&mut a, 4, 5);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "┌────────┐\n│A       │\n└────────┘\n┌────────┐\n│B       │\n└────────┘"
        );
    }

    // ── E5: padding (ink oracle) ─────────────────────────────────────────────
    // ink: renderToString(<Box padding={1}><Text>Hello</Text></Box>, {columns:20}) ===
    //   "\n Hello\n"
    #[test]
    fn e5_box_with_padding() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                padding: Some(Lp::Points(1.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Hello");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(render_to_string(&a, 0, 20), "\n Hello\n");
    }

    // ── E6: text wrapping (ink oracle) ───────────────────────────────────────
    // ink: renderToString(<Box width={8}><Text>hello world</Text></Box>) ===
    //   "hello\nworld"
    #[test]
    fn e6_text_wrap() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(8.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "hello world");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(render_to_string(&a, 0, 80), "hello\nworld");
    }

    // ── E7: overflow:hidden (ink oracle) ─────────────────────────────────────
    // ink: renderToString(
    //   <Box width={5} height={1} overflow="hidden"><Text>hello world</Text></Box>
    // ) === "hello"
    #[test]
    fn e7_overflow_hidden() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(5.0)),
                height: Some(Dim::Points(1.0)),
                overflow_x: Some(Overflow::Hidden),
                overflow_y: Some(Overflow::Hidden),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "hello world");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(render_to_string(&a, 0, 80), "hello");
    }

    // ── E7b: border + overflow:hidden together (ink oracle) ──────────────────
    // The clip border-inset path in walk.rs (clip = rect inset by active border
    // edges) runs ONLY when a border and overflow:hidden coexist — every other
    // overflow test has no border and every border test has no overflow.
    // ink: renderToString(
    //   <Box borderStyle="single" width={7} height={3} overflow="hidden">
    //     <Text>hello world</Text>
    //   </Box>) === "┌─────┐\n│hello│\n└─────┘"
    #[test]
    fn e7b_border_with_overflow_hidden_insets_clip() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(7.0)),
                height: Some(Dim::Points(3.0)),
                border_style: Some(BorderStyle::Named("single".to_owned())),
                overflow_x: Some(Overflow::Hidden),
                overflow_y: Some(Overflow::Hidden),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "hello world");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(render_to_string(&a, 0, 80), "┌─────┐\n│hello│\n└─────┘");
    }

    // ── E8: display:none skipped (ink oracle) ────────────────────────────────
    // ink: renderToString(
    //   <Box flexDirection="column" width={20}>
    //     <Box display="none"><Text>hidden</Text></Box>
    //     <Text>visible</Text>
    //   </Box>) === "visible"
    #[test]
    fn e8_display_none_skipped() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                flex_direction: Some(crate::dom::FlexDir::Column),
                width: Some(Dim::Points(20.0)),
                ..Style::default()
            },
        );
        make_box(
            &mut a,
            2,
            Style {
                display: Some(Display::None),
                ..Style::default()
            },
        );
        make_text(&mut a, 3, "hidden");
        make_text(&mut a, 4, "visible");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 2, 3);
        add_child(&mut a, 1, 4);
        assert_eq!(render_to_string(&a, 0, 80), "visible");
    }

    // ── E9: double border (ink oracle) ───────────────────────────────────────
    // ink: renderToString(<Box borderStyle="double" width={10} height={3}/>) ===
    //   "╔════════╗\n║        ║\n╚════════╝"
    #[test]
    fn e9_double_border() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("double".to_owned())),
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(3.0)),
                ..Style::default()
            },
        );
        add_child(&mut a, 0, 1);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "╔════════╗\n║        ║\n╚════════╝"
        );
    }

    // ── E10: text truncate (ink oracle) ─────────────────────────────────────
    // ink: renderToString(<Box width={8}><Text wrap="truncate">hello world</Text></Box>) ===
    //   "hello w…"
    #[test]
    fn e10_text_truncate_end() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(8.0)),
                ..Style::default()
            },
        );
        make_text_styled(
            &mut a,
            2,
            "hello world",
            Style {
                text_wrap: Some(TextWrap::TruncateEnd),
                ..Style::default()
            },
        );
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(render_to_string(&a, 0, 80), "hello w\u{2026}");
    }

    // ── E11: gap between boxes (ink oracle) ──────────────────────────────────
    // ink: renderToString(
    //   <Box flexDirection="column" gap={1} width={10}>
    //     <Text>line1</Text><Text>line2</Text>
    //   </Box>) === "line1\n\nline2"
    #[test]
    fn e11_gap_column() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                flex_direction: Some(crate::dom::FlexDir::Column),
                width: Some(Dim::Points(10.0)),
                gap: Some(1.0),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "line1");
        make_text(&mut a, 3, "line2");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 1, 3);
        assert_eq!(render_to_string(&a, 0, 80), "line1\n\nline2");
    }

    // ── E12: no-top border (ink oracle) ─────────────────────────────────────
    // ink: renderToString(<Box borderStyle="single" borderTop={false} width={10} height={3}/>) ===
    //   "│        │\n│        │\n└────────┘"
    #[test]
    fn e12_no_top_border() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                border_top: Some(false),
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(3.0)),
                ..Style::default()
            },
        );
        add_child(&mut a, 0, 1);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "│        │\n│        │\n└────────┘"
        );
    }

    // ── E13: deeply nested border+padding (ink oracle) ───────────────────────
    // ink: renderToString(
    //   <Box borderStyle="single" padding={1} width={20} height={7}>
    //     <Box borderStyle="double"><Text>inner</Text></Box>
    //   </Box>) ===
    // "┌──────────────────┐\n│                  │\n│ ╔═════╗          │\n│ ║inner║          │\n│ ╚═════╝          │\n│                  │\n└──────────────────┘"
    #[test]
    fn e13_nested_border_padding() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                padding: Some(Lp::Points(1.0)),
                width: Some(Dim::Points(20.0)),
                height: Some(Dim::Points(7.0)),
                ..Style::default()
            },
        );
        make_box(
            &mut a,
            2,
            Style {
                border_style: Some(BorderStyle::Named("double".to_owned())),
                ..Style::default()
            },
        );
        make_text(&mut a, 3, "inner");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 2, 3);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "┌──────────────────┐\n│                  │\n│ ╔═════╗          │\n│ ║inner║          │\n│ ╚═════╝          │\n│                  │\n└──────────────────┘"
        );
    }

    // ── E14: no-left border (ink oracle) ────────────────────────────────────
    // ink: renderToString(<Box borderStyle="single" borderLeft={false} width={10} height={3}/>) ===
    //   "─────────┐\n         │\n─────────┘"
    #[test]
    fn e14_no_left_border() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                border_left: Some(false),
                width: Some(Dim::Points(10.0)),
                height: Some(Dim::Points(3.0)),
                ..Style::default()
            },
        );
        add_child(&mut a, 0, 1);
        assert_eq!(
            render_to_string(&a, 0, 80),
            "─────────┐\n         │\n─────────┘"
        );
    }

    // ── E15: two text nodes side by side (ink oracle) ────────────────────────
    // ink: renderToString(<Box width={20}><Text>left</Text><Text>right</Text></Box>) ===
    //   "leftright"
    #[test]
    fn e15_two_text_nodes_row() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(20.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "left");
        make_text(&mut a, 3, "right");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 1, 3);
        assert_eq!(render_to_string(&a, 0, 80), "leftright");
    }

    // ── M2-D regression: colorless frame byte-equals the pre-styled output ────
    // After promoting the grid to StyledChar cells, a colorless frame must be
    // byte-IDENTICAL to the old plain path: every cell's `styles` is empty, so
    // `styled_chars_to_string` degenerates to plain `.value` concatenation and
    // `trim_end_matches(' ')` collapses trailing spaces exactly as before.
    // We assert a border-with-text frame (border draw + text write + trailing
    // pad on every interior row) equals its plain string AND carries NO ESC byte
    // — proving the styled machinery emits zero SGR for uncolored input.
    #[test]
    fn m2d_colorless_frame_byte_equals_plain() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                width: Some(Dim::Points(12.0)),
                height: Some(Dim::Points(4.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Hi");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        let out = render_to_string(&a, 0, 80);
        assert_eq!(
            out,
            "┌──────────┐\n│Hi        │\n│          │\n└──────────┘"
        );
        assert!(
            !out.contains('\u{1b}'),
            "colorless frame must contain no SGR escape bytes"
        );
    }

    // ═══ M3-A engine-lifetime seam (ADR-3) ═══════════════════════════════════
    //
    // These tests prove the persist-arena / rebuild-engine-per-frame contract
    // that `InkRoot` (M3-D) relies on: a SINGLE long-lived `Arena` is mutated
    // by ops between renders, and each render drives a FRESH engine via the
    // `build_layout_engine` seam. They are the M3-A correctness gate — the
    // thing the rejected Option B would have risked (silent measure corruption).

    use crate::dom::{Op, apply};

    /// Render the persisted arena through the seam exactly as `InkRoot` will:
    /// build a fresh engine each call, then walk into a grid. Mirrors
    /// `render_to_string`'s body so the two paths cannot drift.
    fn render_via_seam(arena: &Arena, root_id: u32, width: u16) -> String {
        let Some((engine, root_rect)) = build_layout_engine(arena, root_id, width) else {
            return String::new();
        };
        let grid_rows = root_rect.height as usize;
        let grid_cols = root_rect.width as usize;
        if grid_rows == 0 || grid_cols == 0 {
            return String::new();
        }
        let mut grid = Grid::new(grid_rows, grid_cols);
        let rect_fn = |id: u32| engine.computed(id);
        walk(
            arena,
            root_id,
            &rect_fn,
            &|_| None,
            &mut grid,
            crate::render::colorize::ColorLevel::Truecolor,
        );
        grid.get().0
    }

    // ── A1: two sequential renders, SetText between them → measure reflects the
    //        NEW text (this is the load-bearing measure-invalidation proof).
    //
    // The box is width=8. "hi" fits on one line. After `SetText` to
    // "hello world" the fresh-engine rebuild re-`set_measure`s the text node,
    // so the second frame measures the NEW string and wraps it to "hello\nworld"
    // (same oracle as E6). A stale measure closure (Option B's risk) would keep
    // measuring "hi" and produce a wrong frame. One persisted arena, two
    // fresh-engine renders.
    #[test]
    fn a1_seam_settext_between_renders_remeasures() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(8.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "hi");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);

        // Frame 1: short text fits on one line.
        let frame1 = render_via_seam(&a, 0, 80);
        assert_eq!(
            frame1, "hi",
            "frame 1 should render the original short text"
        );

        // Mutate the persisted arena: SetText to a string that wraps at width 8.
        apply(
            &mut a,
            &[Op::SetText {
                id: 2,
                text: "hello world".to_owned(),
            }],
        );

        // Frame 2: a FRESH engine must re-measure the new text and wrap it.
        let frame2 = render_via_seam(&a, 0, 80);
        assert_eq!(
            frame2, "hello\nworld",
            "frame 2 must reflect the new text's measurement (wrap at width 8) — \
             a stale measure closure would still measure \"hi\""
        );
    }

    // ── A2: SetStyle changing the box width between renders → layout reflects
    //        the NEW width. width=20 keeps "hello world" on one line; shrinking
    //        to 8 must wrap it. Proves style mutation on the persisted arena is
    //        honored by the next fresh-engine render.
    #[test]
    fn a2_seam_setstyle_width_change_between_renders() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(20.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "hello world");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);

        let frame1 = render_via_seam(&a, 0, 80);
        assert_eq!(frame1, "hello world", "width 20 keeps the text on one line");

        apply(
            &mut a,
            &[Op::SetStyle {
                id: 1,
                style: Box::new(Style {
                    width: Some(Dim::Points(8.0)),
                    ..Style::default()
                }),
            }],
        );

        let frame2 = render_via_seam(&a, 0, 80);
        assert_eq!(
            frame2, "hello\nworld",
            "shrinking the box to width 8 must wrap the text on the next render"
        );
    }

    // ── A3: node removal mid-tree between renders → removed subtree disappears.
    //        Column of three text lines; RemoveChild + Free the middle node;
    //        the next fresh-engine render shows the tree without it. Proves the
    //        rebuild reads the post-removal arena (no orphaned taffy node from a
    //        reused engine).
    #[test]
    fn a3_seam_node_removal_between_renders() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                flex_direction: Some(crate::dom::FlexDir::Column),
                width: Some(Dim::Points(10.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "alpha");
        make_text(&mut a, 3, "bravo");
        make_text(&mut a, 4, "gamma");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 1, 3);
        add_child(&mut a, 1, 4);

        let frame1 = render_via_seam(&a, 0, 80);
        assert_eq!(
            frame1, "alpha\nbravo\ngamma",
            "frame 1 renders all three column children"
        );

        // Remove the middle child from its parent, then free its slot — the
        // op pair the reconciler emits (RemoveChild on removeChild, Free on
        // detachDeletedInstance, op.rs).
        apply(
            &mut a,
            &[
                Op::RemoveChild {
                    parent: 1,
                    child: 3,
                },
                Op::Free { id: 3 },
            ],
        );

        let frame2 = render_via_seam(&a, 0, 80);
        assert_eq!(
            frame2, "alpha\ngamma",
            "frame 2 must drop the removed middle node — fresh engine reads the \
             post-removal arena with no orphan from a stale tree"
        );
    }

    // ── A4: the seam's frozen-wrapper guarantee — `render_to_string` and a
    //        direct seam render produce byte-identical output for the same
    //        arena. If `render_to_string` ever drifts from the seam, this fails.
    #[test]
    fn a4_seam_matches_render_to_string() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                width: Some(Dim::Points(12.0)),
                height: Some(Dim::Points(4.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Hi");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        assert_eq!(render_via_seam(&a, 0, 80), render_to_string(&a, 0, 80));
    }

    // ═══ M3-B styled-render entry (oracle-parity gate) ════════════════════════
    //
    // Every expected literal below was MATERIALIZED by running the live ink
    // oracle at /home/alpha/rewrite/ink with FORCE_COLOR=3 (chalk level 3) via a
    // scratch `renderToString` probe (test/helpers/render-to-string.ts +
    // force-colors.ts), then deleted. Command (all fixtures in one run):
    //   FORCE_COLOR=3 npx tsx scratch_m3b_oracle.tsx
    // where each fixture is `renderToString(<…/>)` and the bytes are dumped as a
    // JSON-escaped string. The exact oracle JSON output is pinned per test.
    //
    // These tests prove the styled entry (`render_styled`) reproduces ink for
    // `<Text color>` SGR and `<Transform>` callbacks — `<Text color>` SGR lives
    // INSIDE the per-node transform (Text.tsx:94-130 → colorize), so a core test
    // wires `colorize` into the accessor exactly as the napi layer will dispatch
    // to a JS `internal_transform`.

    use crate::render::colorize::{ColorLevel, Kind as ColorKind, colorize, dim};
    use crate::render::walk::TransformAccessor;

    /// An owned output transform — the per-line closure shape the accessor mints
    /// (matches the `Box<…>` inside [`TransformAccessor`]).
    type TextTransform = Box<dyn Fn(&str, usize) -> String>;

    /// Build a `<Text>`-style transform mirroring Text.tsx:94-130's EXACT order:
    /// dimColor → color(fg) → backgroundColor → bold → italic → underline →
    /// strikethrough → inverse. `bold`/`italic`/… resolve through `colorize`'s
    /// named-style branch (they are in STYLE_NAMES), reproducing chalk's bytes.
    /// Each flag is the chalk style name (or `None` to skip).
    fn text_transform(
        dim_color: bool,
        color: Option<&'static str>,
        bg_color: Option<&'static str>,
        bold: bool,
    ) -> TextTransform {
        Box::new(move |s: &str, _i: usize| {
            // These accessor transforms mimic ink's JS-side `<Text>` colorize,
            // which the conformance harness forces to chalk.level=3 — so they pin
            // level-3 (Truecolor) SGR bytes here too.
            let lvl = ColorLevel::Truecolor;
            // Text.tsx:95-97
            let mut out = if dim_color { dim(s, lvl) } else { s.to_owned() };
            // Text.tsx:99-101
            if let Some(c) = color {
                out = colorize(&out, Some(c), ColorKind::Fg, lvl);
            }
            // Text.tsx:103-108
            if let Some(bg) = bg_color {
                out = colorize(&out, Some(bg), ColorKind::Bg, lvl);
            }
            // Text.tsx:110-112
            if bold {
                out = colorize(&out, Some("bold"), ColorKind::Fg, lvl);
            }
            out
        })
    }

    /// Render `<Text …>Test</Text>` at root (Root→Text), with the Text node's
    /// own transform supplied by `mk` (a Text.tsx-order transform). Mirrors the
    /// oracle's `renderToString(<Text …>Test</Text>)`.
    fn render_single_text(text: &str, mk: fn() -> TextTransform) -> String {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, text);
        add_child(&mut a, 0, 1);
        // Accessor: node 1 carries the transform; all others None.
        let t = mk();
        let acc: &TransformAccessor<'_> = &|id: u32| match id {
            1 => Some(Box::new(|s: &str, i: usize| t(s, i)) as _),
            _ => None,
        };
        render_styled(&a, 0, 100, acc, ColorLevel::Truecolor).0
    }

    // ── named color (fg) ──────────────────────────────────────────────────────
    // oracle: renderToString(<Text color="green">Test</Text>)
    //   == "Test"
    #[test]
    fn m3b_named_color_fg() {
        let out = render_single_text("Test", || text_transform(false, Some("green"), None, false));
        assert_eq!(out, "\u{1b}[32mTest\u{1b}[39m");
    }

    // ── hex color (fg) ────────────────────────────────────────────────────────
    // oracle: renderToString(<Text color="#ff8800">Test</Text>)
    //   == "Test"
    #[test]
    fn m3b_hex_color_fg() {
        let out = render_single_text("Test", || {
            text_transform(false, Some("#ff8800"), None, false)
        });
        assert_eq!(out, "\u{1b}[38;2;255;136;0mTest\u{1b}[39m");
    }

    // ── background color ──────────────────────────────────────────────────────
    // oracle: renderToString(<Text backgroundColor="green">Test</Text>)
    //   == "Test"
    #[test]
    fn m3b_bg_color() {
        let out = render_single_text("Test", || text_transform(false, None, Some("green"), false));
        assert_eq!(out, "\u{1b}[42mTest\u{1b}[49m");
    }

    // ── dim ───────────────────────────────────────────────────────────────────
    // oracle: renderToString(<Text dimColor>Test</Text>)
    //   == "Test"
    #[test]
    fn m3b_dim() {
        let out = render_single_text("Test", || text_transform(true, None, None, false));
        assert_eq!(out, "\u{1b}[2mTest\u{1b}[22m");
    }

    // ── bold + color combo (order: color fg inner, bold outer per Text.tsx) ────
    // oracle: renderToString(<Text bold color="red">Test</Text>)
    //   == "Test"
    // (Text.tsx applies color BEFORE bold, so bold's 1/22 wraps the red span.)
    #[test]
    fn m3b_bold_color_combo() {
        let out = render_single_text("Test", || text_transform(false, Some("red"), None, true));
        assert_eq!(out, "\u{1b}[1m\u{1b}[31mTest\u{1b}[39m\u{1b}[22m");
    }

    // ── P6.2 CLEAR_TEXT_STYLE render-byte equivalence (op→apply→render loop) ───
    // The styled→plain transition is pinned at the op-emit (native-style-emit),
    // decode (decode_tests), and apply (op.rs) layers — but nothing renders BYTES
    // to confirm a CLEARED node renders PLAIN. This closes that loop end-to-end.
    //
    // We drive the NATIVE path: `render_styled` with an all-None accessor resolves
    // each node through `resolve_transform` (render/walk.rs), which composes SGR
    // from the node's OWN `text_styling` field — exactly the path the napi layer
    // uses for a simple styled `<Text>`. So applying SetTextStyle{red} then Clear
    // through `apply` (the real op-application code) and rendering twice exercises
    // the whole op→apply→render chain, not a hand-injected transform.
    //
    // Non-vacuity guard: the FIRST render MUST contain the red SGR (`\x1b[31m`) —
    // if it didn't, the node was never actually styled and the byte-identity check
    // below would pass vacuously. The SECOND render (after ClearTextStyle) must be
    // byte-identical to the SAME `Test` node rendered as a never-styled plain node.
    #[test]
    fn p6_2_clear_text_style_renders_plain_bytes() {
        use crate::dom::{Op, TextStyle, apply};

        // Oracle: the SAME content rendered as a never-styled plain node. Built in
        // its own arena so no styling op ever touched it.
        let mut plain = Arena::new();
        make_root(&mut plain, 0);
        make_text(&mut plain, 1, "Test");
        add_child(&mut plain, 0, 1);
        let plain_bytes = render_styled(&plain, 0, 100, &|_| None, ColorLevel::Truecolor).0;

        // The node under test: Root → Text("Test").
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, "Test");
        add_child(&mut a, 0, 1);

        // SetTextStyle{color: red} via the real apply() path, then render NATIVE
        // (all-None accessor → resolve_transform reads `text_styling`).
        apply(
            &mut a,
            &[Op::SetTextStyle {
                id: 1,
                style: TextStyle {
                    color: Some("red".into()),
                    ..Default::default()
                },
            }],
        );
        let styled_bytes = render_styled(&a, 0, 100, &|_| None, ColorLevel::Truecolor).0;

        // Non-vacuity: the styled render really carries the red SGR. Without this,
        // a no-op apply would make the byte-identity below pass for the wrong reason.
        assert!(
            styled_bytes.contains("\u{1b}[31m"),
            "precondition: the red-styled node renders the red SGR (\\x1b[31m); got {styled_bytes:?}"
        );
        // It also diverges from the plain oracle (belt-and-braces: styled ≠ plain).
        assert_ne!(
            styled_bytes, plain_bytes,
            "the red-styled render must differ from the plain render"
        );

        // ClearTextStyle via apply(), then render again — must render PLAIN.
        apply(&mut a, &[Op::ClearTextStyle { id: 1 }]);
        let cleared_bytes = render_styled(&a, 0, 100, &|_| None, ColorLevel::Truecolor).0;

        assert_eq!(
            cleared_bytes, plain_bytes,
            "after ClearTextStyle the node renders BYTE-IDENTICAL to a never-styled plain node (P6.2)"
        );
    }

    // ── transform callback (uppercase) ────────────────────────────────────────
    // oracle: renderToString(
    //   <Transform transform={s => s.toUpperCase()}><Text>hello</Text></Transform>)
    //   == "HELLO"
    // <Transform> renders an ink-text wrapping the inner <Text> ink-text; the
    // uppercase transform is applied via output.write on the OUTER text node.
    // Arena: Root→Text(outer, uppercase)→Text(inner "hello", identity).
    #[test]
    fn m3b_transform_uppercase() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, ""); // outer <Transform> ink-text: no own #text
        make_text(&mut a, 2, "hello"); // inner <Text> leaf
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        let acc: &TransformAccessor<'_> = &|id: u32| match id {
            1 => Some(Box::new(|s: &str, _i: usize| s.to_uppercase())),
            _ => None,
        };
        assert_eq!(
            render_styled(&a, 0, 100, acc, ColorLevel::Truecolor).0,
            "HELLO"
        );
    }

    // ── nested transformers (order proof) ─────────────────────────────────────
    // oracle: renderToString(
    //   <Transform transform={s => `O(${s})`}>
    //     <Transform transform={s => `I(${s})`}>
    //       <Text>x</Text>
    //   </Transform></Transform>)
    //   == "O(I(x))"
    // The inner transform is applied during squash (squash-text-nodes.ts:34-39);
    // the outer via output.write. Arena: Root→Text(outer O)→Text(inner I)→Text("x").
    // Proves innermost-first order: I wraps x, then O wraps that.
    #[test]
    fn m3b_nested_transformers_order() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, ""); // outer <Transform>
        make_text(&mut a, 2, ""); // inner <Transform>
        make_text(&mut a, 3, "x"); // <Text>x</Text>
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 2, 3);
        let acc: &TransformAccessor<'_> = &|id: u32| match id {
            1 => Some(Box::new(|s: &str, _i: usize| format!("O({s})"))),
            2 => Some(Box::new(|s: &str, _i: usize| format!("I({s})"))),
            _ => None,
        };
        assert_eq!(
            render_styled(&a, 0, 100, acc, ColorLevel::Truecolor).0,
            "O(I(x))"
        );
    }

    // ── color + transform combined (squash/write interleave proof) ────────────
    // oracle: renderToString(
    //   <Transform transform={s => s.toUpperCase()}><Text color="green">test</Text></Transform>)
    //   == "TEST"
    // The inner <Text color> colorizes "test" → "\x1b[32mtest\x1b[39m" (in squash),
    // then the outer uppercase transform (via write) uppercases the WHOLE string
    // INCLUDING the SGR letters m→M. The uppercased SGR is the proof that color
    // (inner/squash) runs strictly before the transform (outer/write).
    #[test]
    fn m3b_color_then_transform_interleave() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, ""); // outer <Transform> uppercase
        make_text(&mut a, 2, "test"); // inner <Text color="green">
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        let acc: &TransformAccessor<'_> = &|id: u32| match id {
            1 => Some(Box::new(|s: &str, _i: usize| s.to_uppercase())),
            2 => Some(Box::new(|s: &str, _i: usize| {
                colorize(s, Some("green"), ColorKind::Fg, ColorLevel::Truecolor)
            })),
            _ => None,
        };
        assert_eq!(
            render_styled(&a, 0, 100, acc, ColorLevel::Truecolor).0,
            "\u{1b}[32MTEST\u{1b}[39M"
        );
    }

    // ── height return correctness (multi-line frame) ──────────────────────────
    // oracle: renderToString(
    //   <Box flexDirection="column" width={10}>
    //     <Text>line1</Text><Text>line2</Text><Text>line3</Text></Box>)
    //   == "line1\nline2\nline3" (3 rows)
    // render_styled must return both the string AND height == 3.
    #[test]
    fn m3b_height_return_multiline() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                flex_direction: Some(crate::dom::FlexDir::Column),
                width: Some(Dim::Points(10.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "line1");
        make_text(&mut a, 3, "line2");
        make_text(&mut a, 4, "line3");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 1, 3);
        add_child(&mut a, 1, 4);
        let (out, height) = render_styled(&a, 0, 80, &|_| None, ColorLevel::Truecolor);
        assert_eq!(out, "line1\nline2\nline3");
        assert_eq!(height, 3, "3 column text lines → height 3");
    }

    // ── drift guard: no styles/no transforms == render_to_string + height ──────
    // The styled entry with an all-None accessor must byte-equal render_to_string
    // AND report the correct height. Covers a border-with-text frame (border draw
    // + text write + interior pads): the no-op accessor path is the regression
    // oracle for byte-identity (the corpus proves the same for layout fixtures).
    #[test]
    fn m3b_drift_guard_noop_equals_plain() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                border_style: Some(BorderStyle::Named("single".to_owned())),
                width: Some(Dim::Points(12.0)),
                height: Some(Dim::Points(4.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Hi");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);

        let plain = render_to_string(&a, 0, 80);
        let (styled, height) = render_styled(&a, 0, 80, &|_| None, ColorLevel::Truecolor);
        assert_eq!(
            styled, plain,
            "no-op accessor must byte-equal render_to_string"
        );
        assert_eq!(
            styled,
            "┌──────────┐\n│Hi        │\n│          │\n└──────────┘"
        );
        assert_eq!(height, 4, "4-row bordered box → height 4");
        assert!(
            !styled.contains('\u{1b}'),
            "no-op accessor frame must carry no SGR"
        );
    }

    // ── nested styled text correctness (the real-world case squash threading fixes) ──
    // <Text color="red">a<Text color="blue">b</Text></Text>: ink colors ONLY "b"
    // blue (the inner child's transform applied in squash), with "a" + the blue
    // span both wrapped red by the outer (via write). Materialized from the oracle:
    //   renderToString(<Text color="red">a<Text color="blue">b</Text></Text>)
    //   == "ab"
    // (oracle: FORCE_COLOR=3 renderToString, chalk level 3.) Without squash
    // threading "b" would be colored red, not blue — this is the correctness gate.
    // ── nested same-axis styled text: inner color applies to the CHILD span ───
    // <Text color="red">a<Text color="blue">b</Text></Text>: the inner child's
    // blue transform is applied to ONLY its own folded substring ("b") during
    // squash (squash-text-nodes.ts:34-39); the outer red wraps the whole via
    // write. This is the real-world correctness the squash threading exists for —
    // without it, "b" would be red, not blue.
    //
    // Oracle (FORCE_COLOR=3 renderToString, chalk level 3):
    //   renderToString(<Text color="red">a<Text color="blue">b</Text></Text>)
    //   == "ESC[31ma ESC[34mb ESC[39m"   (single trailing reset)
    //
    // inkferro reproduces this BYTE-FOR-BYTE: the outer red wrap nominally yields
    // a doubled `ESC[39m` close, but the styled-char grid re-tokenizes the line on
    // write and serializes minimal SGR (`styled_chars_to_string`), collapsing the
    // redundant trailing reset — the same single `ESC[39m` chalk's closeRe emits.
    // So no divergence here: the grid's SGR de-duplication absorbs what would
    // otherwise be a same-close-code mismatch. The load-bearing fact is that "b"
    // carries BLUE (the inner child's color via squash), not red.
    #[test]
    fn m3b_nested_styled_text_inner_color_applies_to_child() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, "a"); // outer <Text color="red">: own #text "a"
        make_text(&mut a, 2, "b"); // inner <Text color="blue">b</Text>
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        let acc: &TransformAccessor<'_> = &|id: u32| match id {
            1 => Some(Box::new(|s: &str, _i: usize| {
                colorize(s, Some("red"), ColorKind::Fg, ColorLevel::Truecolor)
            })),
            2 => Some(Box::new(|s: &str, _i: usize| {
                colorize(s, Some("blue"), ColorKind::Fg, ColorLevel::Truecolor)
            })),
            _ => None,
        };
        let out = render_styled(&a, 0, 100, acc, ColorLevel::Truecolor).0;
        // Byte-for-byte oracle match: red "a", blue "b" (inner color on the child
        // span via squash), single trailing reset (grid SGR de-dup == chalk closeRe).
        assert_eq!(
            out, "\u{1b}[31ma\u{1b}[34mb\u{1b}[39m",
            "inner blue must apply to the child span and match the oracle bytes"
        );
    }

    // ═══ static render pass (renderer.ts static branch) ═══════════════════════
    //
    // `render_static` is ink's SECOND render pass: the `<Static>` subtree rendered
    // into its OWN-sized output with skipStaticElements=false, plus a trailing
    // `\n` when a static node is present (renderer.ts:46-66). The main `walk`
    // SKIPS the same static subtree (skipStaticElements=true), so the static
    // content NEVER appears in `plain_output`. Each test mutation-checks BOTH
    // directions: static_output carries the content, plain_output does not.
    // (`Op`/`apply` are already imported by the M3-A seam test section above.)

    // ── static present: subtree → "<body>\n", and main walk omits it ──────────
    // Tree: Root → static Box (position:absolute, so out of flow at (0,0)) → Text.
    // ink's real `<Static>` is `position:absolute` (the JS component sets it), so
    // it occupies no flow space and the live region collapses to empty. We model
    // that layout effect here so the fixture matches ink's static semantics: the
    // live region is empty, and the static output is the box content + newline.
    #[test]
    fn static_present_renders_with_trailing_newline_and_omitted_from_main() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                position: Some(crate::dom::Position::Absolute),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Done");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        // Mark the box static via the real op handler (exercises Op::SetStatic).
        apply(&mut a, &[Op::SetStatic { id: 1, value: true }]);

        // Static pass: the static subtree renders, body + trailing "\n".
        let static_out = render_static(&a, 0, 80, &|_| None, ColorLevel::Truecolor);
        assert_eq!(
            static_out, "Done\n",
            "static output is the static subtree's content plus a trailing newline"
        );

        // Main pass MUST skip the static subtree → empty live region. This is the
        // mutation check: if the skip regressed, plain_output would be "Done".
        let (plain, _h) = render_styled(&a, 0, 80, &|_| None, ColorLevel::Truecolor);
        assert_eq!(
            plain, "",
            "the static subtree must NOT appear in the live (main) output"
        );
    }

    // ── no static node: static_output is "" (the common case, no behavior change) ─
    #[test]
    fn no_static_node_returns_empty_string() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_text(&mut a, 1, "live");
        add_child(&mut a, 0, 1);

        assert_eq!(
            render_static(&a, 0, 80, &|_| None, ColorLevel::Truecolor),
            "",
            "a tree with no static node yields an empty static output"
        );
        // And the main output is unaffected: "live" renders normally.
        assert_eq!(
            render_styled(&a, 0, 80, &|_| None, ColorLevel::Truecolor).0,
            "live"
        );
    }

    // ── reverse-pollution: a LIVE sibling must NOT leak into static_output ─────
    // Tree: Root → [ static Box(position:absolute) → "Done", live Text "live" ].
    // Unlike the other static fixtures, the static subtree is NOT the only content
    // here: a live Text sibling coexists with the static node under the same root.
    // This is the bidirectional pollution check the adversarial review demanded:
    //   • static_output == "Done\n"  catches the static walk ASCENDING to the root
    //     and sweeping in the live sibling;
    //   • render_styled == "live"    catches the converse — the static-skip eating
    //     the live sibling too (it would be "").
    //
    // Child order is load-bearing for the FIRST assertion to discriminate. Layout
    // puts BOTH the static box and the live text at (0,0) (the box is absolute, the
    // live text is the sole flow child), and the static grid is clipped to the
    // box's own 4-wide rect. So if `walk_static` ever ascended to the root, the
    // grid would receive both "Done" and "live" at (0,0) under last-writer-wins —
    // and only the LATER pre-order write survives. By appending the static box
    // FIRST and the live sibling SECOND, a root-ascending leak writes "live" LAST,
    // overwriting "Done" → "live\n" ≠ "Done\n", so the assertion catches it. (The
    // reversed order would let "Done" mask "live" and the test would pass even on
    // the leak — verified empirically.) The correct code, walking from the static
    // node, never sees the live sibling regardless of order.
    #[test]
    fn static_node_does_not_pull_live_sibling_into_static_output() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                position: Some(crate::dom::Position::Absolute),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Done");
        make_text(&mut a, 3, "live");
        add_child(&mut a, 0, 1); // static box FIRST in pre-order
        add_child(&mut a, 1, 2);
        add_child(&mut a, 0, 3); // live sibling SECOND (written last on a leak)
        apply(&mut a, &[Op::SetStatic { id: 1, value: true }]);

        // Static pass: ONLY the static subtree's content, not the live sibling.
        assert_eq!(
            render_static(&a, 0, 80, &|_| None, ColorLevel::Truecolor),
            "Done\n",
            "static_output carries ONLY the static subtree; the live sibling must \
             NOT appear (the walk starts at the static node, never ascends to root)"
        );

        // Live pass: the live sibling renders; the static subtree is skipped.
        assert_eq!(
            render_styled(&a, 0, 80, &|_| None, ColorLevel::Truecolor).0,
            "live",
            "the live (main) output carries the live sibling, with the static \
             subtree omitted"
        );
    }

    // ── multi-line static subtree → each line preserved, single trailing "\n" ──
    // A column of two static text lines: the static body is "a\nb", then the one
    // appended newline (renderer.ts:66) → "a\nb\n". Proves the trailing newline is
    // appended to the WHOLE static block once, not per line.
    #[test]
    fn static_multiline_subtree_single_trailing_newline() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                // position:absolute mirrors ink's `<Static>` (out of flow), so the
                // live region collapses to empty while the static box keeps its
                // own computed width/height for the second-pass grid.
                position: Some(crate::dom::Position::Absolute),
                flex_direction: Some(crate::dom::FlexDir::Column),
                width: Some(Dim::Points(10.0)),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "a");
        make_text(&mut a, 3, "b");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        add_child(&mut a, 1, 3);
        apply(&mut a, &[Op::SetStatic { id: 1, value: true }]);

        assert_eq!(
            render_static(&a, 0, 80, &|_| None, ColorLevel::Truecolor),
            "a\nb\n",
            "multi-line static block keeps its lines and gets one trailing newline"
        );
        assert_eq!(
            render_styled(&a, 0, 80, &|_| None, ColorLevel::Truecolor).0,
            "",
            "the static block is omitted from the live output"
        );
    }

    // ── styled/transform child INSIDE a static node → SGR carried in static_out ─
    // The static pass MUST honor `<Transform>`/`<Text color>` on a node inside the
    // `<Static>` subtree, exactly as the live pass does: `render_static` forwards
    // the SAME `transform_of` accessor to `walk_static`. Here the static text node
    // carries a `green` colorize transform; the static output must contain the SGR
    // escape "\x1b[32m…\x1b[39m". This is the mutation check the adversarial review
    // demanded: if `walk_static`'s `transform_of` were silently no-op'd (or
    // `render_static` stopped threading the accessor into the static walk), the
    // assert below would fail — the static body would be the uncolored "Done".
    #[test]
    fn static_present_honors_styled_transform_child() {
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                position: Some(crate::dom::Position::Absolute),
                ..Style::default()
            },
        );
        make_text(&mut a, 2, "Done");
        add_child(&mut a, 0, 1);
        add_child(&mut a, 1, 2);
        apply(&mut a, &[Op::SetStatic { id: 1, value: true }]);

        // Accessor: the static leaf (id 2) carries a green fg colorize transform,
        // mirroring `<Text color="green">` (Text.tsx:94-130 → colorize). All other
        // ids None — same shape the napi caller mints per id.
        let acc: &crate::render::walk::TransformAccessor<'_> = &|id: u32| match id {
            2 => Some(Box::new(|s: &str, _i: usize| {
                crate::render::colorize::colorize(
                    s,
                    Some("green"),
                    crate::render::colorize::Kind::Fg,
                    ColorLevel::Truecolor,
                )
            })),
            _ => None,
        };

        // Static pass must carry the SGR: green fg wraps "Done", then trailing "\n".
        let static_out = render_static(&a, 0, 80, acc, ColorLevel::Truecolor);
        assert_eq!(
            static_out, "\u{1b}[32mDone\u{1b}[39m\n",
            "the static pass honors a `<Text color>`/`<Transform>` child — the SGR \
             escape MUST appear in static_output (transform_of forwarded to walk_static)"
        );

        // Mutation control: with a NO-OP accessor (the stub the review feared), the
        // same tree yields the uncolored body — proving the SGR above is sourced
        // from the forwarded accessor, not some unconditional colorization.
        assert_eq!(
            render_static(&a, 0, 80, &|_| None, ColorLevel::Truecolor),
            "Done\n",
            "a no-op transform accessor yields the uncolored static body (mutation control)"
        );
    }

    // ── #71: multi-segment <Text wrap=truncate> squashes-then-truncates ──────
    //
    // ink squashes ALL descendant text of an `ink-text` into ONE string FIRST
    // (squash-text-nodes.ts), then measures THAT single fragment once — the
    // `ink-text` is the only node with a yoga measure func; its `ink-virtual-text`
    // children get NO yoga node at all (dom.ts:102/125, measureTextNode at
    // dom.ts:222-246). inkferro USED to attach a measure fn to AND insert a taffy
    // node for EVERY nested segment, so taffy measured each inner segment ALONE in
    // its own wrap mode → a segment WIDER than the box wrapped to ≥2 lines and
    // inflated the text-root's height, where ink (squash-then-truncate) yields ONE
    // line. The fix makes a `Text`/`VirtualText` node a taffy LEAF
    // (`create_layout_nodes` returns after `set_measure`), so the measured unit is
    // the whole squashed subtree — exactly like ink's `ink-text`.
    //
    // SCOPE of the core pin: the per-leaf bug is a MEASURE-time defect. At RENDER
    // time `walk_node`'s Text arm already squashes the whole subtree and truncates
    // once at `rect.width` (divergence map: render path already correct), and an
    // explicit `Box width` PINS `rect.width` regardless of the measure — so render
    // BYTES are not a measure discriminator and are NOT pinned here (the 6 npm byte
    // pins, through the real reconciler + native addon, own those). The core pin
    // routes through `build_layout_engine` (exercising `create_layout_nodes`) and
    // asserts the text-root's computed HEIGHT, which the per-leaf wrap inflates.
    //
    // FAITHFUL arena shape (mirrors the live reconciler; Text.tsx:134 sets
    // `textWrap` on EVERY ink-text/virtual-text, default `'wrap'`): a `Text` root
    // carrying the truncate `text_wrap`, own text None, whose children are
    // `VirtualText` SEGMENTS that EACH carry their OWN `text_wrap = Wrap` (the
    // component default) and the segment string. Without the own-Wrap on the
    // segments the pin would be vacuous: #70's `effective_text_wrap` would make a
    // wrap-less segment INHERIT the root's truncate (height 1) even pre-fix. The
    // own-Wrap is what makes the per-leaf path overflow-then-WRAP, reproducing the
    // inflated height the fix removes.

    /// Build `<Box width=W><Text wrap=MODE><VirtualText wrap=wrap>seg0</>…</Text></Box>`
    /// at root. ids: 0=root, 1=box, 2=text-root, 3/4=segments. Each segment carries
    /// its OWN `text_wrap = Wrap` (the `<Text>` component default — Text.tsx:134).
    fn two_segment_truncate_arena(width: f32, mode: TextWrap, seg0: &str, seg1: &str) -> Arena {
        use crate::dom::{Op, apply};
        let mut a = Arena::new();
        make_root(&mut a, 0);
        make_box(
            &mut a,
            1,
            Style {
                width: Some(Dim::Points(width)),
                ..Style::default()
            },
        );
        // text-root: carries the wrap mode, NO own text (the segments hold it).
        let mut text_root = Node::new(Kind::Text);
        text_root.style.text_wrap = Some(mode);
        a.insert(2, text_root);
        // two VirtualText segments (nested <Text> → ink-virtual-text), each with
        // its OWN default Wrap text_wrap — exactly what Text.tsx:134 emits.
        let mut s0 = Node::new(Kind::VirtualText);
        s0.text = Some(seg0.to_owned());
        s0.style.text_wrap = Some(TextWrap::Wrap);
        a.insert(3, s0);
        let mut s1 = Node::new(Kind::VirtualText);
        s1.text = Some(seg1.to_owned());
        s1.style.text_wrap = Some(TextWrap::Wrap);
        a.insert(4, s1);
        // Wire via apply so `parent` is populated on every edge (op.rs:93).
        apply(
            &mut a,
            &[
                Op::AppendChild {
                    parent: 0,
                    child: 1,
                },
                Op::AppendChild {
                    parent: 1,
                    child: 2,
                },
                Op::AppendChild {
                    parent: 2,
                    child: 3,
                },
                Op::AppendChild {
                    parent: 2,
                    child: 4,
                },
            ],
        );
        a
    }

    // MEASURE-LEVEL discriminator (routes through create_layout_nodes via
    // build_layout_engine). Box width 3 < first segment "AAAA" (4 cols). ink
    // squashes "AAAA"+"BBBB" → "AAAABBBB" and truncates the WHOLE unit at 3 → "AA…",
    // ONE line, so the text-root's computed height is 1. Pre-fix each segment is a
    // taffy leaf measured ALONE in its own Wrap mode: "AAAA"@3 wraps to "AAA\nA"
    // (2 lines), inflating the text-root to height ≥2. The HEIGHT is the
    // discriminator — the box pins the WIDTH to 3 both pre/post, so only height
    // moves (pre ≥2 → post 1).
    #[test]
    fn task71_measure_two_segment_truncate_height_is_one() {
        let a = two_segment_truncate_arena(3.0, TextWrap::TruncateEnd, "AAAA", "BBBB");
        let (engine, _root) =
            build_layout_engine(&a, 0, 80).expect("layout engine builds for the 2-segment tree");
        let text_rect = engine
            .computed(2)
            .expect("the text-root (id 2) is laid out as the measured unit");
        // The whole squash truncates to ONE line. Per-leaf Wrap measure of the
        // overflowing first segment alone inflates this to ≥2.
        assert_eq!(
            text_rect.height, 1,
            "the squashed multi-segment unit truncates to ONE line (per-leaf Wrap measure inflates the extent to >=2)"
        );
    }

    // FULL-FRAME extent pin through render_to_string (plain, #71 case 5 shape but
    // with an OVERFLOWING first segment so the extent actually moves). Box width 3,
    // segments "AAAA"/"BBBB" both Wrap. Oracle-faithful: squash "AAAABBBB" truncated
    // at 3 → "AA…", ONE row, NO trailing blank rows. Pre-fix the per-leaf Wrap of
    // "AAAA"@3 folds to 2 lines → the text-root is height ≥2 → the frame carries
    // trailing blank rows ("AA…\n…"). The full-frame equality (single row, no
    // trailing newline) is the discriminator the box-pinned width cannot mask.
    #[test]
    fn task71_render_plain_overflowing_first_segment_one_row() {
        let a = two_segment_truncate_arena(3.0, TextWrap::TruncateEnd, "AAAA", "BBBB");
        assert_eq!(
            render_to_string(&a, 0, 80),
            "AA\u{2026}",
            "plain multi-segment truncate squashes then truncates once → exactly one row, no trailing blank rows"
        );
    }
}