Keep a pixel frame worn through a shader alive while it is drawn

Changing a palette colour of pixel art flooded the console with Pixi
warnings: "[BindGroup] a 'textureSource' was destroyed while still
bound to a shader", and the same for its sampler. #293 had stopped
this for a drawing, but a frame of pixel art is worn as a cut of the
sheet. The cut has a source of its own, so the sheet looked unbound,
was freed at once and took the cut with it under the shader.

- The check whether a replaced picture is still in use gets its key
  too. TextureLibrary then asks the picture and every cut taken from
  it.
- A sheet with a bound cut waits like a bound picture did since #293,
  and both go together once the shader has taken the new frame.

Found on the way:

- The project the report came from has a sprite wearing a frame of
  an eleven-frame pixel art through a shader asset.
- A nine-sliced sprite wearing the frame showed no warning, even
  without the change. The first try of the e2e check used it.

Tests:
- Gate on melektaus-atx: 236 files, 3577 tests (+1)
- e2e 48: 45 checks (+1, sum 1741). 48l-iii puts a shader on the
  object wearing the second frame, changes a palette colour three
  times and counts the warnings.
- Counter-checks bite: without the cuts in the check the unit test
  fails, and 48l-iii counts 6 warnings for 3 changes.

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

tests/viewport/bound-pictures.test.ts

@@ -97,6 +97,46 @@ describe('a drawn picture a shader still names (#293)', () => {
     expect(r.warnings()).toEqual([]);
   });
 
+  it('waits while a shader names a frame cut from it, as pixel art is worn', () => {
+    // A frame is cut onto a canvas of its own, which needs an image to cut from.
+    vi.stubGlobal(
+      'OffscreenCanvas',
+      class {
+        getContext = () => ({ drawImage: () => {} });
+      },
+    );
+    const library = new TextureLibrary();
+    library.setPictureFactory(
+      () => new Texture({ source: new TextureSource({ resource: {}, width: 8, height: 4 }) }),
+    );
+    const warned = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    const frameOf = (file: string) =>
+      library.get({
+        file,
+        rect: { x: 4, y: 0, w: 4, h: 4 },
+        smooth: false,
+        sourceWidth: 8,
+        sourceHeight: 4,
+        slice: null,
+      })!;
+    library.load('gen:a@1');
+    const cut = frameOf('gen:a@1');
+    const shader = new BindGroup({ 0: cut.source, 1: cut.source.style });
+
+    // A colour of the palette changes: a new revision, and the cut is still in the shader.
+    library.load('gen:a@2');
+    expect(cut.destroyed).toBe(false);
+    expect(library.waitingPictures()).toEqual(['gen:a@1']);
+
+    shader.setResource(frameOf('gen:a@2').source, 0);
+    shader.setResource(Texture.WHITE.source.style, 1);
+    library.load('gen:a@2');
+    expect(cut.destroyed).toBe(true);
+    expect(library.waitingPictures()).toEqual([]);
+    expect(warned.mock.calls.filter((call) => call.join(' ').includes('BindGroup'))).toEqual([]);
+    vi.unstubAllGlobals();
+  });
+
   it('is destroyed right away when no shader names it', () => {
     const r = rig();
     const first = r.library.load('gen:a@1')!;