Preview a sprite at the end of its inspector, placed or as an asset

A sprite's inspector listed its rows but never showed what they add up
to. The picture, its frame, nine-slice, tint and shader could only be
judged in the scene, often far from the object being edited.

- SpritePreview draws the sprite through syncSpriteMesh, the function
  the scene draws it with. Slices, padding, tint and shader come out
  the same without a second path. syncSpriteMesh now takes only the
  three fields of a DrawItem it reads.
- The subject is resolved by previewPicture from the Shader tab, so a
  placed sprite shows its own overrides.
- previewFit is the rule for size and place: whole device pixels per
  unit from 1 on, at most 8, and the corner on a whole device pixel.
  Pixel art stays sharp. A sprite larger than the group shrinks freely.
- A shader with a Time node keeps the preview redrawing once a frame
  while it is on screen. A folded group or a hidden panel stops it.
- New test hook __gm.inspectorSpritePreview().

Finding: the preview redrew on a model change in a microtask at first.
A drawn picture whose revision moved on is retried once, in a
microtask queued by the scene's synchronous redraw. That retry ran
before the preview had let go, and the old pixel art sheet stayed
waiting (e2e 48l-iii read waiting [1,1,1]). The preview now redraws
at once on a model change, as the scene does.

Tests:
- unit: 238 files, 3592 tests (+5 in preview-fit.test.ts), and the
  group list of a placed sprite in sections.test.ts ends in PREVIEW
- e2e 48: ALL PASSED, 47 checks (+2: 48l-i asset preview with
  the frame, 48l-iii placed preview with its shader values)
- counter-checks: without whole-pixel zoom 2 unit tests fail; with
  the microtask redraw 48l-iii fails with waiting [1,1,1]

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/e2e/48-pixelart.mjs

@@ -675,6 +675,26 @@ export async function pixelArt(t) {
     JSON.stringify({ spriteRed, spriteBlue }),
   );
 
+  // 48l-i. The inspector previews the selected sprite as the scene draws it, frame and all.
+  const previewSpots = async () => {
+    const rect = await json('__gm.inspectorSpritePreview()');
+    await settle();
+    if (!rect) return null;
+    const at = (px, py) =>
+      json(
+        `__gm.pixelAt(${Math.round(rect.x + ((px + 0.5) / 32) * rect.w)}, ${Math.round(rect.y + ((py + 0.5) / 32) * rect.h)})`,
+      );
+    return { rect, red: await at(5, 2), blue: await at(10, 10) };
+  };
+  const assetPreview = await previewSpots();
+  check(
+    'the inspector previews the sprite asset with the frame it wears',
+    Boolean(assetPreview) &&
+      colourDistance(assetPreview.red, HEX[RED]) < 12 &&
+      colourDistance(assetPreview.blue, HEX[BLUE]) < 12,
+    JSON.stringify(assetPreview),
+  );
+
   // 48l-ii. Nine-slice on pixel art (#308): 12-pixel borders at scale 2 draw the corner at 2 units a
   // pixel instead of 4, so red (5, 2) and blue (10, 10) move to units (11, 5) and (21, 21). The same
   // spots are read before the borders are set, so a sprite that ignored them could not pass.
@@ -710,7 +730,8 @@ export async function pixelArt(t) {
   //          once and the cut with it, and Pixi warned for the source and its sampler every time.
   await mutate(`
     Object.assign(__gm.state.activeScene.objects.find((o) => o.id === 'pa-object').overrides,
-      { shader: 'adjust-colors', saturation: 0 })`);
+      { shader: 'adjust-colors', saturation: 0 });
+    __gm.state.select({ kind: 'object', holderId: __gm.state.activeScene.id, objectId: 'pa-object', objectIds: ['pa-object'] })`);
   await settle();
   await sleep(300);
   const boundLogFrom = t.consoleLog.length;
@@ -730,10 +751,22 @@ export async function pixelArt(t) {
     boundWarnings.length === 0 && waiting.every((n) => n === 0),
     JSON.stringify({ warnings: boundWarnings.length, waiting }),
   );
+  // The preview of the placed object wears its shader and its own saturation of 0: no colour left.
+  const objectPreview = await previewSpots();
+  const grey = (c) => {
+    const [r, g, b] = [1, 3, 5].map((i) => parseInt(c.slice(i, i + 2), 16));
+    return Math.max(r, g, b) - Math.min(r, g, b) <= 6;
+  };
+  check(
+    "the preview of a placed sprite draws its shader with the object's own values",
+    Boolean(objectPreview) && grey(objectPreview.red) && grey(objectPreview.blue),
+    JSON.stringify(objectPreview),
+  );
   await mutate(`
     const o = __gm.state.activeScene.objects.find((o) => o.id === 'pa-object');
     delete o.overrides.shader;
-    delete o.overrides.saturation;`);
+    delete o.overrides.saturation;
+    __gm.state.select({ kind: 'asset', assetId: 'pa-sprite' })`);
   await settle();
 
   const textureRow = await json("__gm.inspectorField('Texture', true)");