fix(openai realtime): do not commit a turn the server closed itself

[longcw]

Problem: With server-side turn detection the server closes each audio segment itself, and the framework still calls commit_audio() on every client turn. The server answers that second commit with input_audio_buffer_commit_empty, and #6642 only suppressed the error, so every turn still pays for a commit the server rejects.

Fix: The session now handles input_audio_buffer.committed and clears the count of pushed audio, so commit_audio() has nothing left to send. The meaning of commit_audio() does not change, and the error suppression stays for a client commit and a server commit that cross on the wire.

Follows up #6642.

Context for reviewing and coding agents

How to see it

Three unit tests in tests/test_realtime/test_openai_realtime_model.py push a input_audio_buffer.committed event into the session and then call commit_audio(). The first test fails on main, where the handler does not exist. The other two hold the two cases that must keep committing: audio pushed after a server commit, and the echo of the client's own commit when the server does no segmentation.

uv run pytest tests/test_realtime/test_openai_realtime_model.py --unit

Blast radius

commit_audio() has two callers, agent_activity.py:1777 and agent_activity.py:2554, and both run only when _rt_turn_detection_enabled is False, which is the client-side turn taking path. A session that leaves turn taking on the server never reaches them and sees no change. The fix stays inside the openai realtime plugin; other realtime plugins keep their own commit path.

Why the handler is gated on turn_detection

When turn_detection is None the server never commits on its own, so every input_audio_buffer.committed is the echo of a client commit. Audio that arrived while that commit was in flight is still the client's to commit, and the count must survive the echo. With server VAD on, the server segments that audio itself, so clearing the count loses nothing.

Alternatives rejected

The caller in agent_activity cannot make this decision. It knows that server-side turn taking is off, but create_response=False leaves the server detecting and committing turns, and only the plugin sees that setting.

The error suppression alone is not enough. It hides every input_audio_buffer_commit_empty while turn_detection is set, including one that comes from a genuine client mistake, and the needless commit still goes out on each turn.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[longcw]

Closing. #6642 is sufficient.

_handle_error returns on input_audio_buffer_commit_empty before the log, before _emit_error, and before the fatal check, so the second commit changes no state. Either the server buffer holds less than 100ms of unsegmented audio and the commit is rejected, or it holds more and the commit is correct. Neither case harms the session.

The change also does not let us remove the suppression, because a client commit and a server commit can still cross on the wire.