In v4.1.0+, users observed duplicate assistant streams rendering the same
content in two languages simultaneously (e.g. Chinese + English), most often
at the end of a turn.
Root cause: ParentWakeNotifier.requeueWake() unconditionally requeued ANY
wake that arrived during the background-agent-parent-wake post-dispatch
hold window. When a duplicate completion edge fired during that hold, the
same wake was replayed after the hold expired, triggering a second prompt
dispatch and a parallel assistant stream.
The fix compares the new wake against dispatchedParentWakes.get(sessionID)
and drops identical wakes during the gate hold, while preserving the existing
requeue behavior for genuinely-new wakes and failed-dispatch retries.
Regression test added in given/when/then style covering the duplicate-during-
hold scenario (TDD red-then-green).
Fixes#4256Fixes#4019
YeonGyu-Kim