The microtask-coalesce path from 3.3.1 (queueMicrotask + Set so 500
finishing jobs become one queueJobs.filter pass instead of 500) lived
inline in renderer/app.js. Pulled out into lib/coalesced-set.js with
an injectable scheduler so a Node test can drive timing without
async waits.
API: makeCoalescedSet({ apply, scheduler? }) returns
add(id) — queue an id for the next batch
drainSync() — flush synchronously (used by beforeunload)
pendingSize() — diagnostics
isScheduled() — diagnostics
Renderer rewires the previous _pendingDoneRemovalIds + manual
queueMicrotask plumbing to the new helper. Optional-chained: if the
script fails to load, a slower per-event filter runs as fallback.
Coverage:
- multiple adds same tick → 1 apply, all ids deduped
- duplicate ids deduped
- batches between flushes stay independent
- add after flush re-schedules
- drainSync flushes synchronously, queued microtask becomes a no-op
- empty drainSync is a no-op
- throwing apply doesn't lock out subsequent batches
- default scheduler (queueMicrotask) runs eventually
- 5000-id burst still coalesces to 1 apply
137/137 green.
