- thread the realtime version into conversation start and app-server
notifications
- keep playback-aware mic gating and playback interruption behavior on
v2 only, leaving v1 on the legacy path
Add experimental `thread/realtime/*` v2 requests and notifications, then
route app-server realtime events through that thread-scoped surface with
integration coverage.
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Co-authored-by: Codex <noreply@openai.com>