Prod minified bundle crashed with 'can't access lexical declaration 'o'
before initialization' because flush was memoized with stopFlushing in its
deps, and stopFlushing was memoized with flush in its deps — circular.
In dev this still worked (refs paper over TDZ), but Vite's minifier emitted
the declarations in an order that tripped the temporal dead zone.
Extract the interval-clearing into a plain inline helper (clearFlushTimer)
that both flush and stopFlushing call. flush no longer depends on
stopFlushing; the cycle is gone.
