perf(layout): keep grid and table scratch outside layout boxes

Store resolved grid tracks and collapsed-border records only for actual owners in the pass-local world. Freeze the same canonical grid results and consume the same table geometry during paint.

Completes the shared scratch extraction from 96cc04d1e8, after sparse numeric cache allocation.

moli-layout/src/paint/cull.rs

@@ -253,7 +253,7 @@ where
     if !layout_box.style.is_visible() {
         return PaintCullBounds::Empty;
     }
-    let Some(borders) = layout_box.collapsed_table_borders.as_ref() else {
+    let Some(borders) = projection.world.collapsed_table_borders.get(&id) else {
         return PaintCullBounds::Empty;
     };
     let mut bounds = PaintCullBounds::Empty;

moli-layout/src/paint/table.rs

@@ -20,7 +20,7 @@ pub(super) fn project_collapsed_table_borders<N>(
     if !layout_box.style.is_visible() {
         return;
     }
-    let Some(borders) = layout_box.collapsed_table_borders.as_ref() else {
+    let Some(borders) = projection.world.collapsed_table_borders.get(&id) else {
         return;
     };
     let geometry = &projection.boxes[id.index()];

moli-layout/src/projection.rs

@@ -969,7 +969,10 @@ where
                         },
                         horizontal: layout_box.style.uses_horizontal_writing_mode(),
                     });
-                    let resolved_grid_tracks = layout_box.resolved_grid_tracks.clone();
+                    let resolved_grid_tracks = world
+                        .resolved_grid_tracks
+                        .get(&LayoutBoxId::from_index(geometry.id.index()))
+                        .cloned();
                     FrozenLayoutBox {
                         geometry,
                         scroll_extent,

moli-layout/src/stacking.rs

@@ -113,7 +113,7 @@ fn emit_context<N>(
         kind: UnitKind::Contents,
         sequence: next_sequence(sequence),
     });
-    if world.boxes[root.index()].collapsed_table_borders.is_some() {
+    if world.collapsed_table_borders.contains_key(&root) {
         collection.table_collapsed_borders.push(PaintUnit {
             id: root,
             kind: UnitKind::TableCollapsedBorders,
@@ -240,7 +240,7 @@ fn collect_subtree<N>(
     for child in ordered_children(world, id) {
         collect_subtree(world, child, descendant_group, sequence, collection);
     }
-    if layout_box.collapsed_table_borders.is_some() {
+    if world.collapsed_table_borders.contains_key(&id) {
         push_unit(
             collection,
             group,

moli-layout/src/table/collapsed_borders.rs

@@ -468,7 +468,7 @@ where
     {
         world.boxes[part.index()].collapsed_table_border_part = true;
     }
-    world.boxes[root.index()].collapsed_table_borders = Some(borders);
+    world.collapsed_table_borders.insert(root, borders);
 }
 
 pub(super) fn set_collapsed_border_geometry<N>(
@@ -479,7 +479,7 @@ pub(super) fn set_collapsed_border_geometry<N>(
 ) where
     N: Copy + Debug + Eq + Hash,
 {
-    if let Some(borders) = world.boxes[root.index()].collapsed_table_borders.as_mut() {
+    if let Some(borders) = world.collapsed_table_borders.get_mut(&root) {
         borders.set_geometry(columns, rows);
     }
 }

moli-layout/src/taffy_tree.rs

@@ -138,6 +138,7 @@ pub(crate) fn prepare_world_layout<N>(
 where
     N: Copy + Debug + Eq + Hash,
 {
+    world.resolved_grid_tracks.clear();
     for index in 0..world.boxes.len() {
         world.clear_layout_caches(LayoutBoxId::from_index(index));
         let layout_box = &mut world.boxes[index];
@@ -147,7 +148,6 @@ where
         layout_box.layout_children.clear();
         layout_box.positioned_containing_block = None;
         layout_box.inline_static_position = None;
-        layout_box.resolved_grid_tracks = None;
     }
 
     world.viewport_layout.children.clear();
@@ -1880,8 +1880,8 @@ where
         else {
             return;
         };
-        self.boxes[LayoutBoxId::from_taffy(node_id).index()].resolved_grid_tracks =
-            Some(resolved_grid_tracks);
+        self.resolved_grid_tracks
+            .insert(LayoutBoxId::from_taffy(node_id), resolved_grid_tracks);
     }
 }
 

moli-layout/src/world.rs

@@ -263,22 +263,11 @@ pub struct LayoutBox<N> {
     pub(crate) replaced_context: Option<ReplacedContext>,
     pub(crate) replaced_image: Option<crate::LayoutImageResource>,
     pub(crate) css_images: crate::source::LayoutCssImageResources,
-    /// Winning collapsed-table edges owned by the table wrapper for this pass.
-    ///
-    /// The record contains only resolved numeric/color/style data. It is
-    /// produced before Taffy sizing, completed with grid-line geometry after
-    /// sizing, and consumed once by immutable paint projection.
-    pub(crate) collapsed_table_borders: Option<crate::table::CollapsedTableBorders>,
     /// Suppresses ordinary per-box border paint for parts participating in a
     /// collapsed table. Their authored borders have already entered the table
     /// owner's conflict-resolution grid.
     pub(crate) collapsed_table_border_part: bool,
     pub(crate) inline_formatting_context: bool,
-    /// Used Grid tracks produced by the numeric layout pass.
-    ///
-    /// This is browser-owned canonical geometry rather than a retained Taffy
-    /// object. It is frozen with the rest of the layout tree for CSSOM reads.
-    pub(crate) resolved_grid_tracks: Option<LayoutResolvedGridTracks>,
     pub(crate) table_measure_cache: Option<Box<crate::table::TableMeasureCache>>,
     pub(crate) unrounded_layout: Layout,
     pub(crate) final_layout: Layout,
@@ -644,6 +633,12 @@ where
     pub(crate) box_caches: Vec<Cache>,
     /// Box-indexed lookup into compact cache storage; usize::MAX is absent.
     pub(crate) box_cache_slots: Vec<usize>,
+    /// Winning collapsed-table edges, computed and consumed in this pass.
+    /// Empty slots are not embedded in boxes that do not own a table.
+    pub(crate) collapsed_table_borders: HashMap<LayoutBoxId, crate::table::CollapsedTableBorders>,
+    /// Used Grid tracks for actual owners. Their canonical result is frozen
+    /// for CSSOM before this pass-local map is released.
+    pub(crate) resolved_grid_tracks: HashMap<LayoutBoxId, LayoutResolvedGridTracks>,
     pub(crate) source_mapping: HashMap<N, LayoutBoxId>,
     pub(crate) display_contents_mapping: HashMap<N, Vec<LayoutBoxId>>,
     pub(crate) root: LayoutBoxId,
@@ -673,6 +668,8 @@ where
             boxes: vec![root],
             box_caches: Vec::new(),
             box_cache_slots: Vec::new(),
+            collapsed_table_borders: HashMap::new(),
+            resolved_grid_tracks: HashMap::new(),
             source_mapping: HashMap::new(),
             display_contents_mapping: HashMap::new(),
             root: LayoutBoxId::from_index(0),
@@ -1242,10 +1239,8 @@ where
             replaced_context: None,
             replaced_image: None,
             css_images: crate::source::LayoutCssImageResources::default(),
-            collapsed_table_borders: None,
             collapsed_table_border_part: false,
             inline_formatting_context: false,
-            resolved_grid_tracks: None,
             table_measure_cache: None,
             unrounded_layout: Layout::with_order(0),
             final_layout: Layout::with_order(0),