- poll: flush the sentence buffer when the interim bubble is sealed but a
tool is still running (mirrors feedSpeechSession's session.flush), so its
trimmed last sentence isn't held for the whole tool run.
- playSpeechText gains a syncOnly option; the per-sentence fallback uses it
so each sentence no longer re-runs directTtsConfig/resolveSpeakStreamUrl
and a speak-stream WebSocket that already answered fallback.
- single ownedSequence baseline per sentence.