fix: harden desktop turn recovery

[Reza2kn]

Summary

• hardens Desktop active-turn recovery across gateway reconnect/resume flows
• adds gateway-side inflight turn retention/replay for running and failed turns
• blocks sends from detached visible transcripts so context is not silently lost
• emits terminal message.complete error frames with recoverable partial state when turns fail
• fixes Desktop lint/test fallout after the recovery hardening changes

Reliability coverage

• WebSocket reconnect/resume during active turns
• gateway inflight_turn replay/retention
• detached-session send guard
• terminal failed-turn completion/error semantics with partial replay state

Test Plan

• uv run --extra dev --extra messaging python -m pytest tests/tui_gateway/test_protocol.py tests/test_tui_gateway_ws.py -o 'addopts=' -q
• npm run lint --workspace apps/desktop
• npm run typecheck --workspace apps/desktop
• npm run test:ui --workspace apps/desktop
• npm run test:desktop:platforms --workspace apps/desktop

[teknium1]

Thanks for the recovery work. The reconnect and terminal-error direction is useful, but one failed-turn path remains unprotected.

Problems

• tui_gateway/server.py:9140-9174 classifies a returned result["error"] as status="error", emits message.complete, then clears inflight_turn. The PR's new terminal_error_emitted guard only becomes true in the exception handler, so a normal returned error result still has no replay state if its terminal frame is lost during reconnect.

Suggested changes

• Route returned error results through the retained terminal-error path as well, preserving any raw or streamed partial text, and add a regression test covering run_conversation() returning an error result followed by session.resume.
• Port the Desktop portions onto the current split hooks (use-prompt-actions/submit.ts, use-session-actions/index.ts, and use-message-stream/gateway-event.ts) rather than applying the pre-split files.

Automated hermes-sweeper review.

[teknium1]

This guard only retains state after an exception. A normal run_conversation() result with error still takes the regular completion path, leaves terminal_error_emitted false, and clears inflight_turn; retain that logical-error path too so reconnect can replay it.

[OutThisLife]

Superseded by #71184, which re-authors the tui_gateway failed-turn retention onto current main and also routes the returned-error result path through retention (the gap flagged in review), with regression tests for both paths. The desktop portions were rebuilt onto the split hooks. Thanks @Reza2kn, credited via Co-authored-by.