Layout follow-ups drain: anchor + sticky + will-change + transform (L1–L8)

CHANGELOG.md

@@ -582,12 +582,27 @@ tagged release.
   (viewport units) or a font-rendering phase adds them, the sticky
   inset resolver gains new arms (currently closed-match — compiler
   forces the addition).
-- **Both-top-and-bottom-inset sticky — "top wins" (v1 deviation).** Per
-  D4. CSS spec § 6.3 implies a dual-clamp ("sticks to whichever edge
-  the scroll position is currently closer to"); Phase 7's simpler "top
-  wins" matches WebKit/Blink in the common case. Documented test
-  `sticky_both_top_and_bottom_inset_top_wins` is the regression test;
-  flipping it documents the algorithm upgrade. Tracked in follow-ups.
+- **Both-top-and-bottom-inset sticky — dual-clamp (CSS § 6.3).**
+  Superseded the Phase 7 D4 "top wins" deviation.
+  `compute_sticky_displacement` now applies both the top line
+  `U = visible_top + top_px`
+  and the bottom line `L = (visible_bottom - bottom_px) - size`
+  simultaneously per axis: the box pins to `U` when scroll pushes its
+  natural position above it, pins to `L` when scroll pushes it below,
+  and sits at natural flow in between — honoring the bottom inset that
+  the v1 single-edge `if-top else-if-bottom` chain left unreachable. In
+  the degenerate case where the band is shorter than the box (`U > L`)
+  the top edge takes precedence (`.max(U)` re-applied after the bottom
+  `.min(L)`). Each axis still reduces to the single-edge formula when
+  only one inset is set. The v1 regression test
+  `sticky_both_top_and_bottom_inset_top_wins` was flipped to
+  `sticky_both_top_and_bottom_bottom_honored_near_scroll_end`
+  (integration) and the pure unit test to
+  `sticky_both_top_and_bottom_dual_clamp_bottom_honored`; the new
+  `sticky_both_top_and_bottom_conflict_top_precedence` unit fixture
+  locks the `U > L` top-precedence branch and
+  `sticky_both_insets_clamp_at_both_extremes` proves both edges clamp at
+  their respective scroll extremes.
 - **Sticky inside sticky — inner uses outer's natural (un-displaced)
   position.** `world_position` walks Taffy positions; an inner sticky
   inside an outer sticky resolves its threshold against the outer's

crates/buiy_core/src/layout/mod.rs

@@ -25,7 +25,7 @@ pub use systems::{
 };
 pub use tree::LayoutTree;
 pub use types::{
-    AlignContent, AlignItems, AnchorErrorKind, AnchorName, AnchorRef, AspectRatio,
+    AlignContent, AlignItems, AnchorErrorKind, AnchorName, AnchorRef, AspectRatio, AxisDimension,
     BackfaceVisibility, BoxSizing, BreakAfter, BreakBefore, BreakInside, ColumnCount, ColumnFill,
     ColumnRule, ColumnRuleStyle, ColumnSpan, ContainFlags, ContainerType, ContentVisibility,
     Direction, Edges, FlexAxis, FlexGap, FlexWrap, GridAreas, GridAutoFlow, GridLine, Inset,
@@ -139,6 +139,7 @@ impl Plugin for LayoutPlugin {
             .register_type::<Edges>()
             .register_type::<Sizing>()
             .register_type::<Length>()
+            .register_type::<AxisDimension>()
             .register_type::<AspectRatio>()
             .register_type::<Inset>()
             .register_type::<TrackSize>()

crates/buiy_core/src/layout/style.rs

@@ -487,13 +487,19 @@ impl Style {
         self
     }
 
-    /// Ergonomic setter — 2D translate in logical pixels (z = 0).
-    pub fn translate_px(mut self, x: f32, y: f32) -> Self {
-        self.ui_transform.matrix =
-            TransformMatrix::Translate(Length::px(x), Length::px(y), Length::ZERO);
+    /// Ergonomic setter — 2D translate from arbitrary [`Length`]s (z = 0).
+    /// `Percent` resolves against the entity's own border box at compose time
+    /// (x = width, y = height) per CSS Transforms.
+    pub fn translate(mut self, x: Length, y: Length) -> Self {
+        self.ui_transform.matrix = TransformMatrix::Translate(x, y, Length::ZERO);
         self
     }
 
+    /// Ergonomic setter — 2D translate in logical pixels (z = 0).
+    pub fn translate_px(self, x: f32, y: f32) -> Self {
+        self.translate(Length::px(x), Length::px(y))
+    }
+
     /// Ergonomic setter — rotate about the z axis (radians).
     pub fn rotate_z(mut self, radians: f32) -> Self {
         self.ui_transform.matrix = TransformMatrix::Rotate(Quat::from_rotation_z(radians));