fix(tui): preserve detached sessions with active work

[omegazheng]

Summary

• Preserve detached TUI WebSocket sessions that still have resumable work.
• Treat sessions with an in-flight turn, in-progress agent build, or pending prompt/approval as not orphaned.
• Pass the session id into the orphan check so pending prompts can be detected before reaping.

Why

A disconnected desktop/TUI WebSocket transport should not cause active or resumable work to be closed by the orphan reaper. The reaper should only close sessions that are detached and have no active turn, build, or pending user input.

Tests

• Added coverage for detached sessions that are still building, still handling an in-flight turn, or waiting on a pending prompt.
• Verified locally:
  • uv run python -m pytest tests/test_tui_gateway_server.py -q -o 'addopts=' -k 'ws_orphan_reap'
  • Result: 4 passed, 278 deselected

[JLDynamics]

Additional finding from issue #52089 (reported by a user experiencing this bug):

Even when your ws_orphan_reap fix prevents session reaping, there is a SECOND issue: after sleep/wake, the desktop app UI still loses the session reference even though the data persists in state.db. The session survives with end_reason = "active" and all messages intact, but the UI shows a blank conversation.

This means the reaper fix alone (#49900) is necessary but not sufficient. The desktop app also needs to properly recover the session reference after WebSocket reconnection (#47297).

[teknium1]

Thanks for the focused lifecycle fix. Current main still has the relevant gap: tui_gateway/server.py:751-762 classifies a detached session using only _finalized, running, and transport state, and tui_gateway/server.py:775-788 uses that result to close it. Meanwhile, _sess() can start an agent build while running remains false (tui_gateway/server.py:1484-1489), and _start_agent_build() marks that build in progress (tui_gateway/server.py:1321-1325).

The proposed guards align with the established policy in the longer-lived reapers, which already spare pending and not-ready sessions (tui_gateway/server.py:860-867, 908-917). The added regression cases are focused on the missing WebSocket-specific exclusions. The separate desktop reconnection/reference issue noted in the PR discussion remains outside this change's scope.

Automated hermes-sweeper review.