Engine drives device.enableSpawnGating() per armed-session intent;
matched spawns re-attach via the existing attach path and misses
resume immediately. Engagement intent is in-memory only so launches
don't auto-engage gating for sessions armed in a previous run.
ProcessSession gains armingState and lastArmPattern, mirrored in
the SQLite schema. RuntimeEvent.Source.spawnGating carries the
captured/released outcome with wire encoding.
Lab protocol adds update-arming as a SessionOp variant; armed-only
sessions announce themselves with pid 0 and phase detached so peers
can see them before any capture.
Engine.onUserNotification surfaces gating-enable failures using the
clean Frida.Error message.
