fix(core): fail closed when paint workers fail

[chh-ay]

Summary

• make paint workers report ready or fatal, including fatal context loss
• bound worker initialization with a 10-second readiness timeout and route every failure through the existing guarded canvas fallback
• preserve renderer-owned transfer buffers from the cached-view ownership fix and cover healthy, fatal, timeout, duplicate, and destroy-before-ready lifecycles

Public API note

The worker readiness handshake requires adding ready and fatal to the existing exported WorkerAcknowledgement union. That is an additive published API change, so keeping the API baseline byte-identical was impossible. This PR regenerates the public API baseline and generated worker docs. GridEvents["renderer-fallback"], grid.ts, and paint request payloads are unchanged.

Evidence

Pre-fix reproduction: bun test packages/core/test/worker-fallback.test.ts produced 4 pass / 2 fail. Both new cases remained on rendererKind() === "worker" instead of falling back to "canvas" when getContext("2d") returned null or no readiness message arrived.

Post-fix:

• bun test packages/core/test/worker-fallback.test.ts packages/core/test/worker-renderer.test.ts: 18 pass / 0 fail
• bun test packages/core/test: 760 pass / 0 fail
• bun run typecheck: pass
• bun run api:check: pass after the required additive acknowledgement baseline/docs update
• bun run lint: pass (existing oversized-corpus warning only)
• bun scripts/check-import-cycles.ts: 88 modules acyclic
• bun run changeset:ci: patch changeset accepted
• root bun test: 1274 pass / the same 7 known baseline failures
• browser suite: 172 pass across Chromium and Firefox; 14 WebKit launch failures because this workstation lacks libicu74/libxml2/libflite1 and interactive sudo is unavailable. Required CI remains the WebKit gate.

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Project	Deployment	Actions	Updated (UTC)
sheetwrite	Ready	Preview, Comment	Jul 26, 2026 5:59pm