fix: move compression and resize to web worker (#41)

[esau-morais]

Root Cause: WASM compression was running synchronously on the main thread, blocking the browser UI for several seconds when processing large images (especially at high zoom levels). Chrome shows "unresponsive page" dialog when main thread is blocked for too long.

Fix: Moved compression and resize operations to a Web Worker, allowing:

1. Main thread to remain responsive during compression
2. UI updates to happen smoothly
3. Browser to avoid showing "unresponsive page" warnings

---

Note

Moves heavy WASM image processing off the main thread and wires the UI to the worker-backed APIs.

• Add lib/compress.worker.ts to handle compress/resize messages using wasm functions, returning results via postMessage and transferring ArrayBuffers
• Add lib/compress-client.ts to manage a singleton worker, request/response correlation with timeouts, crash handling, and reconstruction of ImageData; exposes compressImage/resizeImage
• Update routes/+page.svelte to import from compress-client, route all compression/resize operations through the worker, and simplify the flow (e.g., recompress on resize/apply)
• Configure Vite (vite.config.ts) with worker.format = "es" for module workers

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Project	Deployment	Review	Updated (UTC)
pixo	Ready	Preview, Comment	Dec 30, 2025 2:32pm

[esau-morais]

@leerob notice that this fixes the root cause, however does not prevent a long compression time when selecting lossy, as it is already expected and commented in https://github.com/leerob/pixo/blob/main/src/png/mod.rs#L63-L65

EDIT: optimal_compression increases over 20x due to Zopfli

[leerob]

bugbot run

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You can kick off a cloud agent using @cursor - e.g. @cursor fix the bug in compress-client.ts.

[leerob]

Thank you!