[macOS/iOS][realtime voice] Voice does not start correctly in existing Codex project threads

Summary

Realtime voice works when started in a new/projectless Codex chat (the Playground-style chat), but it does not start or attach correctly when initiated from an existing chat inside a Codex project. Text turns in the same project chat work normally.

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 project and an existing chat in that project.
3. Start realtime voice from that project chat.
4. Observe whether the voice session starts and remains attached to the selected project thread.
5. Open a new projectless Codex chat and start realtime voice.

Expected behavior

Realtime voice should work for any valid Codex thread, including threads belonging to projects, while preserving the selected project and chat context.

Actual behavior

In this setup, realtime voice is usable in new/projectless chats but fails to start or does not attach correctly in project chats. Depending on the attempt, it can appear stuck, fall back to another thread, or create/use a projectless conversation.

Additional context

The Codex app-server documentation describes realtime as thread-scoped and experimental, but does not document a projectless-only restriction:
https://github.com/openai/codex/blob/main/codex-rs/app-server/README.md

This appears to be a project-thread integration or client capability-gating issue. No private transcripts, cookies, passwords, or user data are attached.