TestInterruptAutoPromotionIgnoresLaterUsageLimitIncrease still relied on
wall-clock polling after the acquire loop moved to a mock clock, so it
could assert before chatd finished its asynchronous cleanup and
auto-promotion work.
Wait on explicit request-start signals and on the server's in-flight
chat work before asserting the intermediate and final database state.
This keeps the test synchronized with the actual processor lifecycle
instead of scheduler timing.
Closes https://github.com/coder/internal/issues/1406
Hugo Dutka