fix(avatar): bun and odango knots take the back hair color

[DoodleBears]

Fixes #19.

Cause

Bun and odango draw their knots in the style's front mask; their back mask is none. Split hair (detailedHair()) merges the back style's front mask into the fringe for rows y <= 7, so the knots became part of the bangs piece. The version 4 piece-color pass therefore gave them to bangsColor, and backHairColor, which only owns masks.back, never painted anything.

Change

• hair() returns a knots mask for bun and odango. The front mask is unchanged, so the knots are drawn exactly as before.
• detailedHair() passes on the back style's knots, excluding any pixel the bangs style itself covers.
• In the version 4 piece-color pass, backHairColor owns the knot pixels and bangsColor no longer does.
• The one exception is a drawn bangs part: it replaces the built-in fringe, so it keeps ownership of whatever it draws.

Compatibility

• Only version 4 recipes that set bangsColor or backHairColor with backHair: 'bun' | 'odango' render differently, and that's the fix.
• Recipes without piece colors take the same code path, so versions 1, 2 and 3 and all seeded faces are unaffected.
• Every golden fixture passes unchanged: botharness-golden, species*, animals, custom-part, pieces.

Tests

New test in pieces.test.ts, run for both bun and odango:

• backHairColor now changes more than 4 cells, all in the knot rows (y <= 7).
• bangsColor and backHairColor share at most the dark outline on the seam between knot and fringe.
• Setting the color to hairColor is a no-op.
• Turned heads (±30°) are recolored too.

The test fails on main and passes with the fix. pnpm verify passes (112 tests).

#20 covers the two look-alike choices from the same audit (buzz bangs, heart vs diamond face). They're occlusion effects, and this PR leaves them unchanged.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • For asset version 4, bun and odango knots now follow the back-hair color instead of the fringe color when hair colors are customized. Recipes using other hairstyles or no custom hair colors are unchanged.

[coderabbitai]

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• Configuration used: defaults
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Reviewing files that changed from the base of the PR and between 369a587 and d382b27.

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📒 Files selected for processing (2)

• CHANGELOG.md
• packages/avatar/package.json

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⚙️ Run configuration

• Configuration used: defaults
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Reviewing files that changed from the base of the PR and between 71e69e8 and 369a587.

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📒 Files selected for processing (3)

• CHANGELOG.md
• packages/avatar/src/figure.ts
• packages/avatar/test/pieces.test.ts

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📝 Walkthrough

Walkthrough

Asset-version-4 hair masks now identify bun and odango knots separately. Recoloring assigns visible knots to back hair rather than bangs, subject to the drawn-bangs condition. Tests cover the updated color ownership.

Changes

Bun and odango knot recoloring

Layer / File(s)	Summary
Separate knot masks packages/avatar/src/figure.ts	The bun and odango branches return separate knot masks. detailedHair excludes knots covered by the built-in bangs front mask.
Recoloring ownership and coverage packages/avatar/src/figure.ts, packages/avatar/test/pieces.test.ts, CHANGELOG.md	Asset-version-4 recoloring assigns visible knots to back hair and excludes them from bangs-color ownership. Tests check recoloring, seam overlap, matching base colors, and two yaws. The changelog records the change.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

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Merge Risk: ⚪ Minimal · up to 369a5

The described version-4 knot recoloring change has focused coverage for bun and odango behavior. No concrete issue requiring resolution before merge is established.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: bun and odango knots now use the back hair color.
Linked Issues check		Issue #19 requires version 4 bun and odango knots to respond to backHairColor instead of bangsColor, with unchanged golden output. hair() now exposes knots for both styles. detailedHair() pa…
Out of Scope Changes check		The reviewed changes are limited to the issue behavior, its changelog entry, and automated regression coverage. The figure.ts mask and color-pass changes implement #19. The pieces.test.ts addition…

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Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (1 skipped: 1 unsupported.)

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