When a turn hit max_iterations, finalize_turn ran three unguarded cleanup
steps after the model's summary — _save_trajectory (file I/O), _cleanup_task_resources
(remote VM/browser teardown), and _persist_session (SQLite write). Any raise
there propagated out of run_conversation, discarding the partial final_response
the caller was waiting for; subprocess wrappers saw an empty stdout with no
traceback (#8049).
Each step is now guarded independently so one failure can't skip the others.
Failures log at ERROR with a traceback and are surfaced on the result dict via
cleanup_errors; the partial response is always returned.
Closes#8049.
