## Why
Delegated turns can begin without a user message, leaving threads without a task preview. Populate the preview from delegated input so these threads are discoverable before a user follow-up.
## What changed
- Extract previews from completed `create_thread` and `send_message_to_thread` outputs in the `codex_app` and `codex_tui` namespaces.
- Unwrap recognized `<codex_delegation>` inputs and decode their escaped task text for display, preserving model content. Keep plain or unrecognized wrappers as text and ignore blank inputs.
- Fill missing previews in state metadata extraction and live thread metadata updates without replacing existing previews or setting the title or `first_user_message`.
## Testing
Add tests for delegation decoding and tool filtering, preview-only metadata updates, preservation of later user-message metadata, and database listing before a user follow-up in both legacy and paginated history modes.
GitOrigin-RevId: f7b3c60ef75e08c76b4084d043e3967bf2bade22
