## Why
Multi-agent V2 spawned threads are controlled by their parent and reject direct
app-server input. The TUI should expose that ownership instead of presenting an
input flow that the server will reject.
## What changed
- Add the experimental `Thread.canAcceptDirectInput` capability for loaded
threads and populate it from the same policy used to validate `turn/start`
and `turn/steer`. Stored, unloaded threads report `null`.
- Carry the capability through TUI thread discovery, selection, startup, and
resume flows, with a compatibility fallback for older app servers.
- Present parent-owned threads as view-only, preserve drafts and queued input,
block agent-directed commands and settings shortcuts, and keep local
navigation and inspection commands available.
## Testing
- Cover V1 writable and V2 view-only spawned threads through selection and
resume.
- Cover composer submission paths, queued and initial input preservation,
allowed navigation commands, settings shortcuts, and the view-only UI.
GitOrigin-RevId: 495ad051249e5577fb0b0c1cc8c40a0998d04918
Felipe Coury
3f0669dbd6