Closing live event stream early hangs in _merge_live_event_streams cleanup

Finding: In google-adk, closing the merged live event stream returned by _merge_live_event_streams (src/google/adk/live/_runner_utils.py) can hang forever if aclose() is called while the internal one-slot merged queue holds an event. The reporter saw this on main at commit 4d06641 and says released google-adk 2.10.0 has the same code (https://github.com/google/adk-python/issues/7357). This is an external report; KFA did not reproduce it. Reported mechanism: the merge's finally block cancels _pump_queued_events. That pump's own finally then awaits merged.put(done_sentinel). Nothing reads merged any more and it is full, so the put never completes. The cleanup waits on the pump, so aclose() never returns. The reporter located the stuck task at the sentinel put around line 302 (https://github.com/google/adk-python/issues/7357). Conditions: the hang is timing dependent and happens only when merged is full at close time. The reporter used a minimal script with no model call. It queued several events on ic._event_queue and used a never-finishing agent stream. It read one event, waited briefly, then called aclose(). The reporter says a 500-trial stress run on Python 3.12 hung in 131 trials on Linux and 157 on Windows. The environments listed were Ubuntu on WSL2 and Windows 11, with Python 3.10 to 3.14. The reporter also said two LiveKit tests that drive a real run_live time out on their machine but pass on GitHub Actions, likely due to timing (https://github.com/google/adk-python/issues/7357). Maintainer status: the issue is closed. A collaborator said the problem was fixed in commit 41bebdc by re-raising the cancellation in the queue pump instead of putting the end-of-stream sentinel into the full queue, so aclose() returns, and that it shipped in v2.11.0 (https://github.com/google/adk-python/issues/7357#issuecomment-5955758975). This is a maintainer claim only. No commit or release link was supplied, and KFA did not verify it. Closure alone is not proof of a fix. Limitations: no workaround was reported. The fix claim is unverified by KFA. The record applies to the reported versions; behavior on versions after 2.11.0 is unknown.