M4.13: motion blur of collapsed precomps and of animated shape / text content

- Collapsed precomps: the renderer records the precomp layers a nested comp is drawn through;
  motion-blur sub-samples re-evaluate their transforms (when their motion blur is on) and map
  times down through each one, so the precomp layer's own motion blurs its nested layers. The
  containing (outermost) comp's shutter applies to collapsed layers. The GPU compositor gets
  this through Renderer::placement.
- Shape and text layers whose content changes within the shutter (compared by its cache key)
  draw their source at Samples Per Frame times and average them; the cache key covers every
  sub-sample's content.
- Tests: tests_motion_blur_depth (collapsed vs flat, the containing shutter, shape content vs
  the same move by Position); each fails without the change.
- Docs: roadmap, parity.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

ROADMAP.md

@@ -10,7 +10,7 @@ once.
 | M1 | Keyframes: temporal and spatial interpolation, Easy Ease, roving, velocity | Done |
 | M2 | Compositing: 38 blend modes, track mattes, parenting, adjustment layers | Done |
 | M3 | Project operations: settings dialogs, layer commands, `.ecproj`, undo, After Effects menu bar | Done (unsaved-changes prompts, Solid / Layer Settings, lock-aware layer commands, safe project files; View ▸ New Viewer still opens only the one locked viewer) |
-| M4 | Preview: precomps, motion blur, cached playback | Mostly done (Preserve frame rate / resolution when nested, one motion blur gate, RAM preview fixes, Cache Frames When Idle; left: motion blur of collapsed precomps and of animated layer content) |
+| M4 | Preview: precomps, motion blur, cached playback | Mostly done (Preserve frame rate / resolution when nested, one motion blur gate, RAM preview fixes, Cache Frames When Idle, motion blur of collapsed precomps and of animated shape / text content; left: content-keyed RAM preview frames) |
 | M5 | Timeline depth: graph editor, keyframe clipboard and dialogs, time remapping, pick-whips, expression editor | Done |
 | M6 | Shapes, masks and footage: shape operators, masks and the pen tool, video and image import | Done |
 | M7 | 3D: 3D layers, cameras, lights, shadows, depth of field, 3D views and camera tools | In review |
@@ -33,7 +33,6 @@ Measured feature by feature in [docs/parity.md](docs/parity.md) (4 October 2026)
 - **≈ 8.5 agent-hours of work remain**: about **2–3 hours of wall-clock time** with five Claude
   Opus 5.5 agents in parallel, ≈ 1 hour without learned models for Roto Brush and face tracking.
 - What is left: GPU kernels for the remaining visual effects, and learned-model quality for Roto
-  Brush and face tracking; in previews, motion blur of collapsed precomps and of animated layer
-  content, and content-keyed RAM preview frames ([parity.md](docs/parity.md#highest-value-gaps-in-order)).
+  Brush and face tracking; in previews, content-keyed RAM preview frames ([parity.md](docs/parity.md#highest-value-gaps-in-order)).
 
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