## What changed
- Add the under-development `transcript_v2` feature for the interactive
transcript composer and turn-selection UI.
- Keep it disabled by default and expose it through the configuration schema
and `codex features enable transcript_v2`.
## Testing
- Verify explicit configuration overrides and CLI persistence for the new
feature.
GitOrigin-RevId: 138ab7851621c066e8121cc3eb6cd4e7299f9c31