fe0a5e10b2
New pruning.py sidecar module with load_pruning_state / save_pruning_state. The sidecar lives at ~/.config/muxplex/pruning.json and is NEVER in SYNCABLE_KEYS — bookkeeping is per-device, not federated. prune_stale_keys(settings, live_keys, *, pruning_state, grace_seconds, now) drops keys from hidden_sessions and view.sessions after they have been missing past the configurable grace period (default 24h, syncable via stale_key_grace_hours). Wired into _run_poll_cycle as step 14 with try/except so failures never abort the cycle. The prune ACTION (settings change) syncs normally via existing LWW; the bookkeeping does not. 24 new tests pass; total muxplex/tests/ = 1263 passed.