Office sample: round 28 — palette-law fix for face/hair blue-collapse (t-141 handoff)

[mahoudeau]

Handoff PR, not for direct merge — t-141 (stage 1: sprites) is already claimed by kassad, this is offered for review/cherry-pick, not landed unilaterally.

What this fixes

t-141's own mission body names "THE PALETTE LAW" as the root cause of the blue-face defect. This PR is that fix.

Root cause: round 25's accent_max_area_frac = 0 (a real fix for JPEG-ringing speckle noise) had a collateral side effect — it disabled the only mechanism that could preserve small-area-but-critical colors (skin/eye/brow) against a 28-color palette budget dominated by the character's much-larger-area suit. Verified mechanically: the best skin-tone color bucket ranked #58 by raw frequency, never surviving the palette_size=28 cut, so every warm face-region cell snapped to the nearest available color — always a dark suit-navy. That's the entire "flat blue face" bug across rounds 14–26.

The fix

Built on top of kassad's round-27 commit (3071ab5), reusing their magenta_hue_score():

• Added it as a second gate in build_shared_palette's opaque-candidate path (round 27's fix only covered the edge-band decontamination path, a different code path).
• Restored accent_max_area_frac to 0.01 (the tool's documented default) across all four manifests, now safe because hue — not the accent toggle — is what keeps noise out.
• New palette_hue_tolerance = 25, calibrated directly against every concrete bad-pixel example cited across rounds 25–27 (min score 38) and every real skin/hair/suit color in the current sheets (max score 17) — wide margin both sides.

Verification

• All four manifests re-ran; every shipped atlas region's sha256 matches its rectify-manifests/report-*.json exactly (byte-for-byte reproducible).
• Determinism confirmed by double-run.
• Sprite pixel dimensions unchanged for every region (pitch/anchor untouched — a color-fidelity fix, not a re-crop).
• Zero magenta-hued opaque palette entries anywhere in the rebuilt atlas.
• An inner-critic pass (mine, not a substitute for the real critic) confirms genuine, non-lateral progress: skin tone, jaw contour, and one legible eye pixel now present where none existed. Does not fully close the craft gap — no eye highlight/brow line/mouth, hair still one flat tone with no shading band or outline. That's feature-level work, likely bounded by cell-count at this pitch, separate from this pipeline bug.

Full writeup in the commit message and in frames.json's round28Fixes.faceHairPaletteStarvation. Evidence screenshots: projects/bureau/deliverables/t-141-handoff-{idle,typing,face-closeup}.png.

Context

t-59 was closed discarded mid-round by consul's re-scope (staged t-141/t-143/t-144 pipeline) while this fix was already built and verified. t-141 was already claimed by kassad when this landed, so it's offered here rather than pushed into their active work or claimed out from under them. Diff and cherry-pick freely — additive on top of round 27, not a replacement.

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Generated by Claude Code

[mahoudeau]

Backlog purge (t-274): superseded by PR #50 (round 5 of the same t-141 work, critic-passed) and conflicting with main. The palette-law fix it carried landed in later rounds.