fix(svg): preserve dimension contract under sw/sh and pixelRatio < 1

[chiefcll]

Summary

#41 introduced two unintended changes to SVG texture dimensions that broke the existing texture-svg VRT (Loaded Event Test: Fail). Both narrow tweaks in loadSvg.

Regressions

1. Sub-1 stage.pixelRatio downscales the raster.
The examples app sets logicalPixelRatio = resolution / appHeight = 720 / 1080 = 0.667 (examples/index.ts:78). #41's Math.ceil(targetW * pixelRatio) multiplied by that, so a 181-wide SVG rasterized to 121 pixels — lower resolution than before, the opposite of the HiDPI sharpness goal. Tests 1, 2, 3 hit this.

2. sw/sh no longer drive texture size when w/h are unset.
Pre-fix, getImageData(sx, sy, sw, sh) returned an sw × sh ImageData regardless of canvas size, so a node that set only srcWidth/srcHeight got a texture sized to the source crop. #41 keyed targetW/H off width || naturalWidth, ignoring sw, so the texture became natural-size with the crop stretched into it. Test 4 (rocko2 partial: expects 81×218, was getting 181×218) hit this.

Fix

Two small adjustments to textureSvg.ts:57-59:

const targetW = width || sw || img.naturalWidth || img.width;
const targetH = height || sh || img.naturalHeight || img.height;
const ratio = pixelRatio > 1 ? pixelRatio : 1;

• sw/sh fall through when w/h are null, restoring the "crop dims drive texture dims" contract.
• pixelRatio > 1 ? pixelRatio : 1 clamps so sub-1 stages never downscale. HiDPI upscaling (the original intent) still applies.

The fallback to naturalWidth || width is intentional — naturalWidth is preferred (intrinsic SVG dims), with .width as the back-stop for browsers that return 0 for SVGs without explicit width attributes.

Verification

Captured a fresh chromium-ci texture-svg-1.png via the Docker runner. All five existing assertions pass:

Test	Pre-this-PR	This PR	Expected
1. rocko (no w/h)	121×146 ✗	181×218 ✓	181×218
2. elevator (no w/h)	134×179 ✗	200×268 ✓	200×268
3. lightning (w=125, h=25)	84×17 ✗	125×25 ✓	125×25
4. rocko2 (srcW=81, no w/h)	121×146 ✗	81×218 ✓	81×218
5. 404 failure event	Pass ✓	Pass ✓	(no dims)

loaded / failed events were never broken — they fire and carry a dimensions payload as before. This PR just makes that payload match the pre-#41 contract.

Test plan

• pnpm build clean
• pnpm test — 193/193 pass
• Local + Docker VRT for texture-svg — all 5 assertions pass
• Refreshed visual-regression/certified-snapshots/chromium-ci/texture-svg-1.png

🤖 Generated with Claude Code