[SandroMaglione]

Two fixes to pixel check / pixel fix grid detection, found by scoring the fixer on xprite-pixelate's benchmark (MIT) and pixel-bench v1 (MIT), through checkImage, the path the CLI runs.

What changes

1. The grid is read on the subject (detectGrid in grid.ts). It finds the box holding the subject: its visible pixels, or, on an opaque picture whose border is one color, the pixels away from that color. It keeps a 4 px margin, so the outline stays where the edge profiles see it. It detects there, then shifts the offsets back onto the whole picture. Output size and recipes are unchanged.
2. An upscale is not pixel art at its own size (isNative in report.ts). If under 5% of neighbouring pixels change color and the picture has more than 32 colors, it is judged as a fix. A grid that can't be found now reports needs-person instead of clean at full size. The color limit keeps flat parallax layers counted as 1× art.

Evidence (exact size)

	main	this PR
AI suite (1746 cases + 98 sparse-on-white cases I added)	65.0%	76.0%
Small sprite on a clear canvas	24.0%	99.0%
Small sprite on an off-white canvas	25.5%	95.9%
pixel-bench v1 (7651 cases)	38.2%	40.1%
v1: wrong size but trusted (fixable/clean)	4168	2889
AI suite: upscales wrongly called 1× art	200	4

Rows for this PR use the crop as measured before the 4 px margin was added. On a 722-case sample, the margin moved exact sizes by under a point.

Real 1× art: 165 of 178 corpus images were left alone before and 170 after. 280 shipped PNGs from Still Time, Landkeep and Spirit Call give identical verdicts. The crop measured alone won 211 AI cases and lost 15.

Known limits

• Cells under about 5 px are still not detected well. Clean 2–3× upscales stay the main gap on pixel-bench v1 (xprite 87%). Few-colour ones are still reported clean.
• Drift (cells that grow across the picture) is not addressed here. A prototype of cuts that walk cell to cell did well on AI pictures but needs a full-suite run first.
• The gate's thresholds (5%, 32 colors) were set on this corpus. When the gate is wrong, the result is needs-person, never a bad fix.

Tests

• New tests: a sprite on a much larger clear canvas, on an off-white canvas, and a drifting upscale whose grid is not found. All three fail on main.
• A flat few-color picture stays 1× art (guards the color limit).
• pnpm run check passes. No public TypeScript API changed, so no website build.

🤖 Generated with Claude Code