Zachary D. Rowitsch 327e31795b Implement positioning completeness (CSS 2.1 §10.3.7, §10.6.4, §11.1.2, §9.6.1) ...

Story 1.3: Complete positioning support including auto offset resolution,
clip rect, fixed scroll behavior, and containing block edge cases.

Key changes:
- Refactored calculate_absolute_layout() for full §10.3.7/§10.6.4 compliance
- Implemented clip: rect() parsing, style computation, layout, and paint
- Fixed sticky child recursion in process_deferred_absolutes
- Fixed shrink-to-fit abs_cb using unpositioned padding_box
- Added collapsed_borders handling in offset_children
- Propagated CSS clip to descendant stacking contexts
- Tightened rect() parser to reject garbage between rect and (
- Added tracing::warn for unrecognized clip tokens
- Replaced hardcoded epsilon with MARGIN_EPSILON constant
- Added RTL unimplemented comments on over-constrained resolution
- Strengthened tests: exact assertions, delta comparisons, new coverage
- 4 new tests: negative offsets, clip suppression, padding edge distinction
- 5 golden tests (222-226), promoted WPT absolute-tables-016

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

2026-03-13 20:20:08 -04:00

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