feat(voice): add UserTurnLimitOptions to interrupt long user speech

[longcw]

Summary

Adds a configurable limit on how long a user can speak before the agent is given a chance to interrupt. Accumulates word count and wall-clock duration across consecutive user turns.

When a threshold is crossed, the framework fires UserTurnExceededEvent and invokes Agent.on_user_turn_exceeded. The default implementation calls session.generate_reply(..., allow_interruptions=False, tool_choice="none") with instructions to politely cut in with a short reply. Users can override the hook for custom behavior.

API

AgentSession(
    turn_handling={
        "user_turn_limit": {"max_words": 100, "max_duration": 30.0},
    },
)

Both thresholds default to None (disabled). Set either or both.

Coordination

AgentActivity._user_turn_exceeded_task waits for the normal EOU-triggered response to resolve before firing the hook — if the agent reaches speaking on its own, the callback is skipped.

[devin-ai-integration]

✅ Devin Review: No Issues Found

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