Verify Lezama composer guard and fail-open diagnostics

Reported risk: context-monitor.sh CA nudge could inject tmux keys while a user was composing. Investigation found the composer-occupancy gate already guarded the sole typed transport under its flock (since v4.80). v4.86 / c3222e2 adds pane-specific stderr diagnostics for prior indistinguishable fail-open exits: capture-pane rc, exception, history-line, and no-glyph. Lezama receipt: deployed actuator ExecStart=/home/rob/.local/bin/context-monitor.sh, commit c3222e23b9b5d5431bf010b889858b8e7992c8dd, VERSION=4.86; composer corpus PASS (14 cases); manual post-pull service run started 2026-08-25T07:20:19Z sampled five sessions with zero FAIL-OPEN lines. Verification boundary: no live typing-during-nudge reproduction, so this validates the current normal path and observability rather than proving every TUI state.