fix(server): serialize chokidar watcher batches to prevent heap growth

[Schrotti77]

Problem

On Windows the OK server uses the chokidar watcher fallback (@parcel/watcher crashes with STATUS_STACK_BUFFER_OVERRUN on long/non-ASCII paths, see #1207). chokidar (ReadDirectoryChangesW) emits more granular events than inotify, and each 50ms batch calls handleRawEvents, which readFile()s every changed file.

When a batch is still mid-drain (slow disk, many files, active sync/backup tool) and the next 50ms timer fires, the new batch launches independently — overlapping async work piles up and the Node heap grows without bound on event storms.

Fix

Serialize batches by chaining them on an inFlight promise in startChokidarWatcher. Batches drain strictly one at a time; a batch that lands while another is draining waits its turn. The .catch remains load-bearing: it keeps the chain alive after an error so later batches don't deadlock.

Regression test

file-watcher-chokidar-fallback.test.ts — new describe "chokidar backend — batch serialization":

• onDiskEvent counts active drains (active++, hold 200ms, active--), tracks maxActive
• write to existing file → wait until active === 1 (batch 1 draining)
• write again → batch 2 lands mid-drain
• wait 600ms, expect(maxActive).toBe(1)

Verified:

• Without fix: test fails (maxActive reaches 2 — batches overlap)
• With fix: 11/11 tests pass, typecheck clean

Tested with forceBackend: 'chokidar' on Linux — no Windows needed to exercise the path.

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[robert-inkeep]

hi @Schrotti77 could you follow the @CLAassistant instructions? and i'll see this through