The 3s gate was too tight — users reading the prompt and retyping
consistently blow past it and get stuck in a loop ("press /clear
again within 3s" forever). Fixes:
- bump CONFIRM_WINDOW_MS 3_000 → 30_000
- drop the time number from the confirmation message to remove the
pressure vibe: "press /clear again to confirm — starts a new session"
- reset the gate from createSlashHandler whenever any non-destructive
slash command runs, so stale arming from 20s ago can't silently
turn the next /clear into an unintended confirm
- export the gate + isDestructiveCommand helper for that wiring
- add armed() introspection method
Follow-up to #4069 / 3366714b.
75377feb07