fix(voice): finish transcription iterators when sessions close during setup

[rioyu123]

Summary

This pull request fixes a hang when an application closes a streamed transcription session during setup and then waits for its transcript consumer to finish.

After the WebSocket connects, the SDK sends session.update and waits for the response. Calling close() at this point stops the connection and background tasks, but transcribe_turns() can remain blocked because the event processor that normally signals completion has not started yet.

Signal completion from the close path as well as normal event processing, using one shared guard to avoid duplicate completion markers. Task cleanup, transcript delivery, and error selection remain in their existing paths. Public APIs and WebSocket messages are unchanged.

This addresses application-initiated close(), not the server-initiated setup disconnect discussed in #4585. It does not include that PR's setup error propagation changes.

Test plan

• Added real loopback WebSocket regressions that wait until the server receives session.update, then close the session before session.updated. Both tracing modes reproduce the hang on the base and finish with the fix.
• Covered repeated close, active-session close, server close, provider errors, and consumer cancellation, including transcript delivery, owned-task completion, and tracing cleanup.
• Full Voice suite: 230 passed on Windows and Linux. The STT tests also passed with four parallel workers: 32 passed.
• Full repository verification passed on Linux / Python 3.14.4: formatting, lint, Mypy, Pyright, and 9,693 tests; 33 skipped. No live OpenAI speech calls were made.

Issue number

N/A

Checks

• I've added new tests, if relevant
• I've run .agents/skills/code-change-verification/scripts/run.sh
• I've confirmed all verification steps pass
• If using Codex, I've run /review before submitting this PR

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-14T00:30:19.408039Z	e81f829	Draft marked ready
🔒 Security Review	✅ Completed 2026-09-14T00:31:01.697404Z	e81f829	Draft marked ready

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[github-actions]

This PR is stale because it has been open for 10 days with no activity.

[rioyu123]

Still relevant: current main still doesn't signal completion on the close path. I reran tests/voice/test_openai_stt.py (32 tests) against this PR's head and all pass. The change remains scoped to application-initiated close during setup. Could this stay open for review?

[jbeckwith-oai]

Reviewed the complete diff and the setup/close lifecycle. Closing during setup can leave the transcript consumer waiting after its producer tasks stop; the guarded completion signal after cleanup fixes that path without changing the public API or protocol handling. The controlled setup regression and terminal-path coverage fit the scope. No blocking findings. Tests were inspected, not executed locally; the current CI checks are green.