fix(frontend): resolve stale closure in chatSearch.ts debounce (#1225)

[Mercy017]

Root cause

debounce() in chatSearch.ts had three related bugs:

1. Stale fn closure — fn was captured at debounce() call time and never updated. When callers recreated their callback (e.g. an inline arrow function on each render), the debounced wrapper kept calling the original, stale function.
2. Stale timer reference — timer was never reset to null after the timeout fired. Future clearTimeout(timer) calls operated on an already-expired ID, giving a false sense of cancellation.
3. No cancel() method — there was no way for a caller to abort a pending invocation on component unmount, causing callbacks to fire against unmounted state.

Fix (src/lib/chatSearch.ts)

• Introduced latestFn variable inside debounce; added updateFn(newFn) on the returned function so callers can swap the underlying callback without rebuilding the debounced wrapper.
• timer = null is now set inside the setTimeout callback so the reference is always accurate.
• Added cancel() method that clears and nulls the pending timer.
• Exported the DebouncedFn<T> interface for typed usage.

Regression tests (src/lib/chatSearch.test.ts)

Six new tests under describe('debounce') covering:

• Basic fire-after-delay
• Debounce (rapid successive calls)
• updateFn calls the new fn, not the original (stale-closure regression)
• cancel() prevents firing
• Timer reference is null after fire (no stale ID)
• Call after cancel works correctly

Closes #1225
Closes #1223

[drips-wave]

@Mercy017 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits