Use when writing a Vitest test for a react-router useBlocker unsaved-changes guard in this repo — specifically an intentional-navigation handler (Edit / Submit / Cancel) that uses flushSync(() => setIsNavigating(true)) before navigate() to bypass the blocker. A test that reads the blocker predicate after act() passes even when flushSync is removed, so it does not guard the fix. Trigger on any test touching isNavigating, useBlocker, flushSync, or a *.hooks.js navigation-blocker handler.