fix(producer): recover from worker crashes instead of hanging the render (#1132)

* 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>

.fallowrc.jsonc

@@ -22,6 +22,9 @@
     // Worker entry points loaded dynamically by their *Pool.ts companions.
     "packages/producer/src/services/pngDecodeBlitWorker.ts",
     "packages/producer/src/services/shaderTransitionWorker.ts",
+    // Test fixture worker, spawned by path via the pools' workerEntryPath
+    // option from the crash-recovery tests; has no import-graph referrer.
+    "packages/producer/src/services/__fixtures__/crashOnMessageWorker.mjs",
     "scripts/*.{ts,mjs,js}",
     "scripts/*/run.mjs",
   ],