* fix(producer): recover from worker crashes instead of hanging the render
Both the shader-transition and png-decode-blit worker pools freed a
crashed worker's slot (busy=false, current=null) but left it in the slot
list and never marked it dead. A later run() then selected the dead slot
via slots.find(s => !s.busy) and dispatched to its terminated worker,
where postMessage is a silent no-op (no throw, no reply) — so the task
promise never settled. In the HDR hybrid capture loop, which pipelines
blends across N DOM workers and awaits every dispatch, that wedges the
whole render with no fail-fast.
The crash handlers also never drained the queue, so a queued task could
wait forever for a slot that had died.
Mark a slot dead on error/exit, exclude dead slots from dispatch and from
run()'s slot selection, and fail fast: when no live workers remain, reject
queued tasks and reject new run() calls rather than hanging. This keeps
the pools' existing no-respawn, fail-fast intent; it just actually fails
fast instead of wedging.
Adds crash-recovery tests to both pools via a fixture worker that throws
on its first message, asserting the in-flight task, queued tasks, and
subsequent run() calls all settle rather than hang.
* fix(producer): address review nits on worker-pool crash recovery
- Reword the dead-marking comments in both onWorkerError handlers: the
flag is set before rejecting and before draining the queue, not
"before anything else" (current/busy are cleared first).
- Rename the shader pool's all-slots-die test to match the png pool's
equivalent; the size-2 fixture crashes every worker, so there are no
surviving workers serving.
---------
Co-authored-by: Carlos Alcaraz <193642530+calcarazgre646@users.noreply.github.com>
## Summary
PR 3 of 5 in the hf#732 decomposition stack. Adds a `worker_threads`-based pool that runs the shader-transition blend (one of 15 transition shaders) on a fixed-size worker pool. **No production wiring yet** — the pool stands alone; PR 4 wires it.
The shader blend is a hot inner loop over every pixel of every transition frame at 16bpc. Moving it off the main event loop removes the JS-event-loop ceiling that capped throughput in earlier hf#732 iterations.
### New files
- `packages/producer/src/services/shaderTransitionWorker.ts` — worker entry. Imports from `@hyperframes/engine/shader-transitions` (zero-import TS source).
- `packages/producer/src/services/shaderTransitionWorkerPool.ts` — fixed-size pool. Uses `transferList` so the 16bpc HDR `from`/`to`/`out` buffers move by ownership.
- `packages/producer/src/services/shaderTransitionWorkerPool.test.ts` — 6 vitest tests pinning byte-equivalence across all 15 shaders, transferList correctness, pool lifecycle. All pass.
### Build wiring
- `packages/cli/tsup.config.ts`: third tsup entry emits `dist/shaderTransitionWorker.js`.
- `packages/producer/build.mjs`: fourth esbuild entry for direct producer consumers.
- `packages/engine/package.json`: adds `./shader-transitions` subpath export.
## Stack
Stacked on top of #757 (PR 2: pngDecodeBlit pool). No behavior change in any render.
## Test plan
- [x] 6 pool tests pass
- [x] Producer + engine typecheck clean
- [x] oxlint clean
— Vai
