The incremental Edge/non-streaming TTS fallback re-polls the pending reply every 150 ms until the response finishes. Nothing cancelled that timer when the hook unmounted or the speech session was dropped, so a tick could fire after teardown (CI: 'ReferenceError: window is not defined' at use-voice-conversation.ts poll, from the rearm test file). The poll's cancel is now held in a ref, cleared by dropSpeechSession() and by an unmount effect.
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