feat(loaders): add a debounce option to query loaders

[kianbazza]

Summary

Query loaders accept debounce (ms, default 0): createQueryLoader, createSWRQueryLoader and createVanillaQueryLoader. The engine holds the search until it stops changing, then passes it to the loader. The loader's query and enabled both come from the held search, so a search that minQueryLength disallows is never run. While a newer search waits, the loader counts as fetching. useAsyncMenuCoordinator().isAnyFetching can drive a "working" indicator, and the menu doesn't treat the search as finished.

type "a", "ab" within the debounce  -> the loader sees "", then "ab" (never "a")

Evidence

New loader-debounce.test.tsx (fake timers, 7 tests):

• Only '' and 'ab' reach the fetcher.
• With minQueryLength: 2, '' is never fetched while 'ab' waits.
• Empty stays hidden during the wait and shows after.
• isAnyFetching is true during the wait.
• A loader that reports the new search a render late, or whose real result looks exactly like the waiting state, still settles on the right rows.
• debounce: 0 fetches every keystroke as before.

Merge Danger

Door: two-way

Blast Radius: none by default

Default 0 keeps today's behaviour.

Closes UI-558

[vercel]

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Project	Deployment	Actions	Updated
ui-canary	Ready	Preview	Sep 29, 2026 2:31pm UTC

[linear-code]

UI-558