refactor: remove internal/layout/Engine (ADR-032 CACHE-030)

CHANGELOG.md

@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - **Collapsible animation glitch on Wayland** ([#152](https://github.com/gogpu/ui/issues/152)) — force final redraw after animation completes + full-window `wl_surface.damage_buffer` on root repaint. Confirmed by @porjo.
 
+### Removed
+
+- **`internal/layout/Engine`** (ADR-032 CACHE-030) — centralized layout engine with 0 production usage. Per-widget layout caching is now fully handled by `widget.LayoutChild` on `WidgetBase`. -769 lines of dead code.
+
 ### Changed
 
 - **deps:** gg v0.50.1 → v0.50.2, gogpu v0.43.1 → v0.43.4, wgpu v0.30.8 → v0.30.9, goffi v0.5.5 → v0.5.6

internal/layout/bench_test.go

@@ -18,14 +18,6 @@ func (b *benchLayoutable) Layout(_ geometry.Constraints) geometry.Size {
 func (b *benchLayoutable) Children() []Layoutable { return nil }
 func (b *benchLayoutable) ID() uint64             { return 0 }
 
-// cachableLayoutable is a Layoutable with a non-zero ID for cache benchmarks.
-type cachableLayoutable struct {
-	benchLayoutable
-	id uint64
-}
-
-func (c *cachableLayoutable) ID() uint64 { return c.id }
-
 // --- Flex layout benchmarks ---
 
 func newFlexWithChildren(n int) *FlexContainer {
@@ -158,44 +150,3 @@ func BenchmarkGridLayout10x10(b *testing.B) {
 		grid.Layout(constraints)
 	}
 }
-
-// --- Layout engine cache benchmarks ---
-
-func BenchmarkLayoutCacheHit(b *testing.B) {
-	engine := NewEngine()
-	engine.EnableCache(true)
-
-	child := &cachableLayoutable{
-		benchLayoutable: benchLayoutable{preferredSize: geometry.Sz(100, 50)},
-		id:              42,
-	}
-	constraints := geometry.BoxConstraints(0, 800, 0, 600)
-
-	// Warm up cache with one layout call.
-	engine.Layout(child, constraints)
-
-	b.ReportAllocs()
-	b.ResetTimer()
-	for b.Loop() {
-		engine.Layout(child, constraints)
-	}
-}
-
-func BenchmarkLayoutCacheMiss(b *testing.B) {
-	engine := NewEngine()
-	engine.EnableCache(true)
-
-	child := &cachableLayoutable{
-		benchLayoutable: benchLayoutable{preferredSize: geometry.Sz(100, 50)},
-		id:              42,
-	}
-	constraints := geometry.BoxConstraints(0, 800, 0, 600)
-
-	b.ReportAllocs()
-	b.ResetTimer()
-	for b.Loop() {
-		// Mark dirty before each layout to force recomputation.
-		engine.MarkDirty(child.ID())
-		engine.Layout(child, constraints)
-	}
-}

internal/layout/doc.go

@@ -1,4 +1,4 @@
-// Package layout provides the internal layout engine implementation for gogpu/ui.
+// Package layout provides internal layout algorithm implementations for gogpu/ui.
 //
 // This package is INTERNAL and not intended for public use. It implements
 // constraint-based layout algorithms used by the widget system.
@@ -7,11 +7,14 @@
 //
 // The layout package provides several layout algorithms:
 //
-//   - [Engine]: Manages layout passes with caching and dirty tracking
 //   - [FlexContainer]: CSS Flexbox-style layout (row, column, wrap)
 //   - [VStack], [HStack], [ZStack]: Simplified stack layouts
 //   - [GridContainer]: Basic grid layout with rows and columns
 //
+// Per-widget layout caching is handled by [widget.LayoutChild] (ADR-032),
+// not by this package. Container widgets call LayoutChild instead of
+// child.Layout directly, which checks the per-widget cache on WidgetBase.
+//
 // # Constraint-Based Layout
 //
 // Layout follows a constraint-passing model similar to Flutter:
@@ -25,15 +28,6 @@
 // forces a specific size (min == max), while a "loose" constraint allows
 // flexibility (min = 0).
 //
-// # Layout Engine
-//
-// The Engine manages layout passes efficiently:
-//
-//   - Single-pass layout for simple hierarchies
-//   - Multi-pass layout for intrinsic sizing
-//   - Caching of layout results to avoid redundant calculations
-//   - Dirty tracking for incremental layout updates
-//
 // # Flexbox Layout
 //
 // FlexContainer implements a simplified CSS Flexbox model:
@@ -70,11 +64,4 @@
 //
 // This package is used internally by the UI framework. Application code should
 // use the public layout widgets instead of directly using this package.
-//
-//	// Internal framework usage
-//	engine := layout.NewEngine()
-//	flex := layout.NewFlexContainer(layout.Row, layout.JustifyStart, layout.AlignStretch)
-//	flex.AddChild(child1, layout.FlexItem{Grow: 1})
-//	flex.AddChild(child2, layout.FlexItem{Grow: 2})
-//	size := engine.Layout(flex, constraints)
 package layout