## What changed
- Add `codex-realtime-webrtc` with a length-prefixed, 256-byte JSON control protocol for `hello`, `ready`, `close`, and `closed` messages.
- Add a hardened `codex-voice-host` binary that validates protocol and build compatibility, handles orderly shutdown and parent pipe loss, and exposes its build commit.
- Keep this initial foundation limited to process lifecycle management; it does not open audio devices, load native plugins, negotiate WebRTC, or enable voice in the TUI.
## Testing
- Exercise the helper as a subprocess, covering handshake, explicit close, parent pipe loss, malformed frames, incompatible builds, and invalid message order.
GitOrigin-RevId: 6d8d7dd7ba5c4886879882d79314d235f6ab7cf4
