Prepare automatic TUI recap generation (#40697)

## What changed

- Schedule recap eligibility checks when an unfocused thread changes, and cancel them when focus returns or recap state is replaced.
- Add bounded structured recap requests with stale-result rejection, normalized output, and one retry per turn revision.
- Harden temporary structured threads by reading the effective configuration and disabling all discovered MCP servers, tools, skills, and environment access.

## Testing

- Cover recap timers, focus changes, failed turns, output bounds, stale results, and retry behavior.

GitOrigin-RevId: eebf50059763928e9a2444b14d51648e0bdff4a8