fix(desktop): bake the Classic face on whole pixels at density 1

[doodlewind]

What changed

At rasterDensity 1 the Classic theme's 12.5px face drew no comma and no semicolon, and nine other marks lost or misplaced pixels. src/system-ui/gen-assets.ts now bakes the 12.5px slots at density 1 from outlines snapped to whole device pixels.

Cause. The generator snaps W95FA's outlines to a 40-unit grid with a 10-unit x phase. That is the device pixel grid of the 12.5px slots at density 2 (40 units per device pixel). At density 1 a device pixel is 80 units, and the font's vertical edges sit at 50 + 80k units (1768 of the 1790 x coordinates of the ASCII glyphs), so the 40-unit snap left every vertical edge in the middle of a device pixel. A few glyphs are also drawn a fraction of a pixel off in y. The bake logged slot19 … (AA 86.13%) for density 1, and the hard threshold then dropped whatever covered half a pixel.

Fix. loadSnapped(step, phase) takes the grid. The density-2 bakes and the 25px slot keep (40, 10); the 12.5px slots at density 1 use (80, 50). The generator's alignment assertion (AA ≤ 2%) now runs at both densities, and a new assertion fails the bake when any mapped glyph but the space has no ink.

What moves. w95fa-19.bin and w95fa-20.bin (density 1). The other eight atlases are byte-identical (sha256 compared before and after). In the two that change, no glyph's advance or left-bearing shift changes, so text measures and wraps as before; the header's cell width drops by one pixel (12 to 11, and 13 to 12 for the bold slot).

Eleven glyphs change their density-1 bitmap: " ' ) * , - ; = ^ ` ~. The comma and the semicolon were empty; the others gain the pixels the threshold dropped or move to the nearest whole pixel. Cell rows of slot 19, main on the left:

 ','  row  9  .......   .#.....      '-'  row 6  .####..   .......
      row 10  .......   #......           row 7  .......   #####..

 ';'  row  7  .......   .#.....      '"'  row 0  .......   #.#....
      row  9  .......   .#.....           row 1  #.#....   #.#....
      row 10  .......   #......           row 2  #.#....   #.#....

Why

Pocket Studio runs the System UI in a browser canvas at density 1. Its Classic theme showed "Your games the workbench and your settings open here." in About and "evan Draft" in its lists. The same holds for any density-1 host of this shell, including the browser preview.

Verification

Run in a clean clone of this branch with the pinned PocketJS submodule (0ca1b362), after bun run setup.

Command	Result
bun shells/desktop/src/system-ui/gen-assets.ts	density 1: slot19 … (AA 0.00%), was 86.13%; density 2 unchanged
sha256 of src/system-ui/fonts/*.bin before and after	2 of 10 differ: w95fa-19.bin, w95fa-20.bin
bun run check	exit 0: 3DS 40, iPod 72, desktop unit 61, sim 6, wrap 7 (4 new), text 6, touch 66 pass; 0 fail

New coverage in test/wrap-op.test.ts, which already loads the generated atlas: every ASCII glyph but the space has ink in slots 19 and 20 at both densities; no coverage sample is partial; each glyph's advance is equal at both densities; the comma and the semicolon draw at density 1. With gen-assets.ts from main, the first and the last of these fail, naming , and ;.

Looked at in Pocket Studio's laptop (800×600 canvas, density 1, Classic): the commas are back in the list rows and in the About dialog, and the rest of the text is unchanged.

Not run locally, left to CI: desktop test:rust, desktop build, desktop package:linux, desktop test:web, the site build and its smoke check.

🤖 Generated with Claude Code