Verified quality high; layout monolith remains main cost.

- ✓ **proof**
  - release build: 2.6s, 0 warnings
  - clippy: 0 warnings, all targets
  - sole dependency: unicode-width
- ✓ **design**
  - B6/B14 refs bind behavior to code
  - `render_scene_with_checks` verifies output
  - signed `Scene` keeps exact bounds
- ✓ **tests ×4**
  - behavior.rs contract scenarios
  - golden.rs byte snapshots
  - scene.rs frame invariants
  - quality.rs geometry predicates
- ⚠ **layout**
  - `layout_fit`: 556 lines
  - `layout_fit` mixes ranking · sizing · special cases
  - `layout.rs`: 1,730 lines, 40% project
  - accumulated heuristics lack decomposition

→ Decomposition sketch available.