## Summary
This PR promotes Mentions 2.0 (unified TUI mention popup) to stable and
enables it by default.
- Keep `mentions_v2` as a temporary rollback path to the legacy split
popups (`--disable mentions_v2`).
- Add feature-default and snapshot coverage for the default experience.
## Prior work
- [#19068 — Unified mentions in
TUI](https://github.com/openai/codex/pull/19068)
- [#22375 — Use plugin/list to get plugins for
mentions](https://github.com/openai/codex/pull/22375)
- [#23363 — Unified mentions tweaks and rendering
polish](https://github.com/openai/codex/pull/23363)
## Test plan
- Launch Codex without any feature overrides.
- Type `@` in the TUI composer.
- Confirm the unified mentions menu opens and displays filesystem,
plugin, and skill results.
canvrno-oai
1bd6b4c41a