fix: prevent race condition in listener iteration

[gn00295120]

Summary

Fixed a race condition in OpenAIRealtimeWebSocketModel._emit_event() where the listeners list could be modified during async iteration, causing RuntimeError: list changed size during iteration.

Problem

The _emit_event() method iterates over self._listeners while calling await listener.on_event(event):

for listener in self._listeners:  # Iteration
    await listener.on_event(event)  # Await point - yields control

During the await, other code (e.g., cleanup) can call remove_listener(), modifying the list mid-iteration.

Crash scenario:

1. Session emits event → _emit_event() starts iterating listeners
2. At await listener.on_event(), control returns to event loop
3. Cleanup runs → calls remove_listener() → modifies list
4. Control returns to iteration → RuntimeError

This is realistic because remove_listener() is called during session cleanup (session.py:761).

Solution

Create a shallow copy of the listeners list before iteration:

for listener in list(self._listeners):  # Copy prevents modification issues
    await listener.on_event(event)

This allows safe concurrent modifications without affecting the ongoing iteration.

Testing

• All 23 existing tests in tests/realtime/test_openai_realtime.py pass
• No behavioral changes, only defensive coding

Impact

• Prevents crashes during concurrent listener management
• Common in cleanup scenarios where session removes itself as listener
• Minimal performance impact (shallow copy of small list)

[Copilot]

Pull Request Overview

This PR fixes a race condition in the event emission mechanism where concurrent listener list modifications during async iteration could cause runtime errors. The fix creates a snapshot of listeners before iteration to prevent RuntimeError: list changed size during iteration when listeners are removed during event processing.

Key changes:

• Added defensive copying in _emit_event() to prevent race condition when listeners list is modified during async iteration
• Added explanatory comment documenting the purpose of the list copy

---

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[seratch]

@codex review

[seratch]

This is a kind of edge case improvement but looks good to me

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

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