[layer][shape] fix stale shape on resize, harden external mask handling

[honghaoz]

Summary

• Fix mask reverting to a stale shape: the live-frame block captured the shape at setup; it now reads the layer's current shape, so shape updates and animateShape survive later resizes.
• Harden external mask manipulation: shape = nil no longer destroys a mask the shape API didn't install; setting/animating a shape reinstalls the shape-managed mask if the mask was removed or replaced externally; the previously installed mask layer is untracked to avoid a permanent leak.
• Document the shape↔mask contract and all edge cases on shape; disable implicit animations for in-place mask path updates.

Test plan

• swift test --filter CALayer_ShapeTests` (25 tests; 6 new regression tests, all verified to fail against the old implementation)

Summary by CodeRabbit

• Bug Fixes

  • Improved shape masking when masks are removed or replaced externally.
  • Preserved user-installed masks when shapes are cleared or animated.
  • Ensured shape masks recalculate correctly after layer bounds changes.
  • Prevented incorrect mask animations and restored the correct shape mask when needed.

• Tests

  • Added coverage for mask replacement, removal, bounds changes, and shape animation behavior.

[coderabbitai]

📝 Walkthrough

Walkthrough

CALayer shape masking now tracks its managed mask layer, preserves externally installed masks, reinstalls managed masks when replaced, and updates paths using current shapes and bounds. Animation falls back to direct application when the installed mask is not shape-managed, with expanded regression tests.

Changes

Shape-managed mask tracking

Layer / File(s)	Summary
Mask tracking and shape updates ChouTiUI/Sources/ChouTiUI/Universal/CoreAnimation/CALayer+Shape.swift	Adds weak associated storage for the shape-managed mask and updates shape changes based on whether the current mask matches the tracked layer.
Mask setup and animation handling ChouTiUI/Sources/ChouTiUI/Universal/CoreAnimation/CALayer+Shape.swift	Replaces stale tracked masks, recalculates paths during frame changes, and skips animation when an external mask is installed.
Shape mask behavior tests ChouTiUI/Tests/ChouTiUITests/Universal/CoreAnimation/CALayer+ShapeTests.swift	Tests bounds changes, external mask preservation and replacement, stale-mask untracking, and direct shape application without path animation.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant CALayer
  participant ShapeManagedMask
  participant ExternalMask
  CALayer->>ExternalMask: External mask replacement
  CALayer->>ShapeManagedMask: Reinstall managed mask on shape update
  CALayer->>ShapeManagedMask: Apply target path directly when masks differ

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main changes: fixing stale shape behavior on resize and improving external mask handling.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch layer-shape-mask-fixes

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[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.87%. Comparing base (ddfb474) to head (fd1fdad).

Files with missing lines	Patch %	Lines
...ouTiUI/Universal/CoreAnimation/CALayer+Shape.swift	97.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   95.79%   95.87%   +0.08%     
==========================================
  Files         120      120              
  Lines        4873     4900      +27     
==========================================
+ Hits         4668     4698      +30     
+ Misses        205      202       -3     

Flag	Coverage Δ
ChouTiUI	95.87% <97.36%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ouTiUI/Universal/CoreAnimation/CALayer+Shape.swift	96.93% <97.36%> (-0.25%)	⬇️

... and 1 file with indirect coverage changes

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