Addresses review feedback on 7787626:
1. Deleted->Created at the same path is a file replacement, not a no-op.
Previous coalescing dropped both Created->Deleted and Deleted->Created;
the latter left the server with no signal to re-read replaced content.
Now: Deleted->Created collapses to Changed, Created->Changed keeps
Created (server didn't know the file at all). Extracted coalesce() so
the matrix is reviewable in one place.
2. setPatterns([]) (server unregistered all watchers) stopped chokidar
but left pending events + timers intact, so a queued batch could
still fire after the server stopped caring. Now drains via
cancelPending() before stopping chokidar.
3. Added ready() returning a promise resolved by chokidar's initial-scan
'ready' event. Production daemon doesn't need to await it (LSP
handshake gives chokidar ample wall-time), but tests now use it
instead of fixed 200ms sleeps - deflakes the suite on slower
filesystems and addresses the (narrow) startup race where a file
created during chokidar's initial crawl could be missed.
4. Unit tests replace 11 hardcoded sleeps with watcher.ready(), and add
coverage for the two coalesce fixes plus the unregister-drains case.
Evan Reichard
0aa44bedc4