fix(media): encode blurhash with canvas-coerced dimensions

src/app/workers/media.worker.test.ts

@@ -0,0 +1,65 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+type Post = { id: number; hash?: string; error?: string };
+
+// OffscreenCanvas coerces dimensions to unsigned integers, like the real platform.
+class StubOffscreenCanvas {
+  width: number;
+
+  height: number;
+
+  constructor(width: number, height: number) {
+    this.width = width >>> 0;
+    this.height = height >>> 0;
+  }
+
+  getContext() {
+    const { width, height } = this;
+    return {
+      drawImage: () => undefined,
+      getImageData: () => ({
+        data: new Uint8ClampedArray(width * height * 4),
+        width,
+        height,
+      }),
+    };
+  }
+}
+
+const setupWorker = async () => {
+  vi.resetModules();
+  const posts: Post[] = [];
+  let messageHandler: ((event: { data: unknown }) => void) | undefined;
+  vi.stubGlobal('OffscreenCanvas', StubOffscreenCanvas);
+  vi.stubGlobal('self', {
+    addEventListener: (type: string, handler: (event: { data: unknown }) => void) => {
+      if (type === 'message') messageHandler = handler;
+    },
+    postMessage: (message: Post) => posts.push(message),
+  });
+  await import('./media.worker');
+  if (!messageHandler) throw new Error('worker did not register a message handler');
+  return { posts, messageHandler };
+};
+
+describe('media.worker blurhash', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it('encodes blurhash when requested dimensions are floats', async () => {
+    const { posts, messageHandler } = await setupWorker();
+    const bitmap = { close: vi.fn<() => void>() };
+
+    expect(() =>
+      messageHandler({
+        data: { id: 1, type: 'blurhash', bitmap, width: 512, height: 170.496 },
+      })
+    ).not.toThrow();
+
+    expect(bitmap.close).toHaveBeenCalledOnce();
+    expect(posts).toHaveLength(1);
+    expect(posts[0]?.error).toBeUndefined();
+    expect(typeof posts[0]?.hash).toBe('string');
+  });
+});

src/app/workers/media.worker.ts

@@ -34,7 +34,9 @@ const handleBlurHash = (req: BlurHashRequest): void => {
     }
     ctx.drawImage(bitmap, 0, 0, width, height);
     const imageData = ctx.getImageData(0, 0, width, height);
-    post({ id: req.id, hash: encode(imageData.data, width, height, 4, 4) });
+    // The canvas coerces dimensions to integers, so use imageData's real size:
+    // encoding with the requested (possibly float) size mismatches the pixels array.
+    post({ id: req.id, hash: encode(imageData.data, imageData.width, imageData.height, 4, 4) });
   } finally {
     bitmap.close();
   }