[iOS][realtime voice] New voice sessions reopen the same thread and can interleave transcripts

Summary

When starting multiple Codex realtime voice sessions from the iPhone remote client, a new session repeatedly reopens or attaches to the same previously active chat instead of staying in the newly selected chat. In this setup, this appears to be a regression: the behavior was not observed previously.

Environment

• Host: macOS on Apple Silicon
• Codex/ChatGPT desktop app: 26.727.51351 (build 6119)
• Client: ChatGPT iOS app using Codex remote voice

Steps to reproduce

1. Pair the iPhone client with the Mac Codex host.
2. Open an existing Codex chat and start realtime voice.
3. End the voice session.
4. Return to the chat list and open a different chat or start a new chat.
5. Start realtime voice again, and repeat with another chat.

Expected behavior

Each voice session should remain attached to the thread selected when it was started. Ending a session should not cause a later session to silently reuse the previous thread, and transcripts should remain isolated to their originating thread.

Actual behavior

The voice session often reopens or attaches to the same prior thread. The UI can appear to be in another chat while the voice transcript is added to the old thread, producing mixed or interleaved conversation history.

Related context

This is voice-specific and may be related to same-thread turn/session routing, but it is distinct from generic mobile thread hydration or persistence issues. A related non-voice report is #34767.

No private transcripts, cookies, passwords, or user data are attached.