Render overlay canvas in a worker

[aidenybai]

Summary

• move overlay selection, drag, and grabbed-box painting into a dedicated worker using a transferred OffscreenCanvas
• bundle the worker source at build time and instantiate it from an inline blob
• share one renderer between the worker and the normal main-thread canvas fallback
• preserve DPR, Display P3, zoom, and animation behavior, with coverage for both rendering paths

Why

The existing canvas layers still ran their animation and compositing loop on the main thread. This isolates that work where supported while retaining the current canvas behavior in browsers without transferable offscreen canvases.

Validation

• nr build
• nr typecheck
• nr lint
• nr format
• E2E_ENVIRONMENT=vite-plus-development nr test -- e2e/overlay-canvas-worker.spec.ts e2e/zoom-canvas.spec.ts (164 unit tests and 3 focused browser tests)

---

Summary by cubic

Render the overlay canvas in a dedicated worker via a transferred OffscreenCanvas, with a main-thread fallback. Preserves DPR, Display P3, zoom, and animation behavior, and bundles the worker inline for reliable startup.

• New Features

  • Added worker-backed overlay renderer with OffscreenCanvas transfer; shared renderer used for both worker and main-thread paths.
  • Bundled worker source at build time and instantiated from a blob URL.
  • Added backend detection and a data-react-grab-overlay-backend attribute for observability.
  • Improved label fade handling and animation scheduling across both paths.
  • Added e2e tests for worker and fallback paths, plus a pixel diff utility; updated zoom test to use screenshot diffs.

• Dependencies

  • Added esbuild to bundle the inline worker.

^{Written for commit cbc9761. Summary will update on new commits.}

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Project	Deployment	Actions	Updated (UTC)
react-grab-storybook	Ready	Preview, Comment	Jul 20, 2026 6:04am
react-grab-website	Ready	Preview, Comment	Jul 20, 2026 6:04am

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commit: cbc9761