## Why
Losing an external app-server connection can leave a submission's outcome uncertain. The TUI must preserve local work without retrying it or allowing stale server events to trigger more actions.
## What changed
- Enter an offline state when an external app-server transport disconnects during startup, event streaming, or submission.
- Keep conversation drafts, queued input, expanded pastes, attachments, and agent-overview input editable while blocking submissions, remote actions, and automatic queue replay.
- Show a connection-lost notice that directs users to copy their work and relaunch, while retaining `Ctrl-C` and an empty-composer `Ctrl-D` as quit shortcuts.
- Cancel pending views and asynchronous work, and ignore stale completions after the disconnect. Embedded app-server behavior is unchanged.
## Testing
Added unit, snapshot, and pseudo-terminal coverage for lost startup and mutation replies, offline draft editing, queued-input recovery, stale-event quarantine, agent-overview behavior, and end-to-end preservation without reconnection or resubmission.
GitOrigin-RevId: 7219a95fad676dda447d625db9e465345b469d58
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