perf: handle large file watch event batches

src/main/runtime/rpc/methods/file-watch-event-batcher.test.ts

@@ -0,0 +1,38 @@
+import { tmpdir } from 'os'
+import * as path from 'path'
+import { describe, expect, it, vi } from 'vitest'
+import type { FsChangeEvent } from '../../../../shared/types'
+import { createFileWatchEventBatcher } from './file-watch-event-batcher'
+
+const LARGE_EVENT_COUNT = 150_000
+
+function buildFileWatchEvents(count: number): FsChangeEvent[] {
+  const events: FsChangeEvent[] = []
+  const root = path.join(tmpdir(), 'orca-file-watch-batch')
+  for (let index = 0; index < count; index += 1) {
+    events.push({
+      kind: 'update',
+      absolutePath: path.join(root, `file-${index}.txt`)
+    })
+  }
+  return events
+}
+
+describe('createFileWatchEventBatcher', () => {
+  it('accepts large watcher event bursts', () => {
+    const emit = vi.fn()
+    const batcher = createFileWatchEventBatcher(path.join(tmpdir(), 'worktree'), emit)
+
+    batcher.push(buildFileWatchEvents(LARGE_EVENT_COUNT))
+    batcher.flush()
+
+    const payload = emit.mock.calls[0]?.[0] as
+      | { type: string; worktree: string; events: FsChangeEvent[] }
+      | undefined
+    expect(payload?.type).toBe('changed')
+    expect(payload?.events).toHaveLength(LARGE_EVENT_COUNT)
+    expect(payload?.events.at(-1)?.absolutePath).toBe(
+      path.join(tmpdir(), 'orca-file-watch-batch', `file-${LARGE_EVENT_COUNT - 1}.txt`)
+    )
+  })
+})

src/main/runtime/rpc/methods/file-watch-event-batcher.ts

@@ -38,7 +38,11 @@ export function createFileWatchEventBatcher(
       if (nextEvents.length === 0) {
         return
       }
-      events.push(...nextEvents)
+      // Why: file watchers can report huge bursts; spreading them into push can
+      // exceed JavaScript's argument limit before the batch has a chance to flush.
+      for (const event of nextEvents) {
+        events.push(event)
+      }
       const now = Date.now()
       if (firstEventAt === 0) {
         firstEventAt = now