[feat](alarm): add a durable per-device delivery ledger

pg_notify and the socket fan-out are not durable, so an offline phone used to miss a trigger forever and no-auto-stop would leave it ringing at nobody. Write one ledger row per enabled subscription in the trigger transaction, replay what a subscription still owes on every socket connect, and clear a row only on an explicit ack (live socket ack or ackAlarm); alarmStatus is a read-only check-in that answers 409 ERR_ALARM_TRIGGERED_OFFLINE with the missed frame. Ack is idempotent, and a destroyed alert cascades its debt away so a client is never told it missed an alarm that no longer exists.

src/realtime/notify.go

@@ -36,26 +36,24 @@ const NotifyChannel = "alarm_events"
 // the one that served the trigger request — fans the event out to its own
 // subscribers.
 type NotifyPayload struct {
-	AlertID         string `json:"alertId"`
-	EventID         string `json:"eventId"`
-	Action          string `json:"action"`
-	Message         string `json:"message"`
-	AutoStopSeconds int    `json:"autoStopSeconds"`
-	CreatedAtMs     int64  `json:"createdAtMs"`
+	AlertID     string `json:"alertId"`
+	EventID     string `json:"eventId"`
+	Action      string `json:"action"`
+	Message     string `json:"message"`
+	CreatedAtMs int64  `json:"createdAtMs"`
 }
 
 // Frame converts the transport payload into the wire frame. ServerTime is the
 // EVENT time, not the delivery time, so every instance and every client agrees
-// on when the alarm started (and therefore on the auto-stop countdown).
+// on when the alarm started.
 func (p NotifyPayload) Frame() AlarmFrame {
 	return AlarmFrame{
-		Type:            "alarm",
-		AlertID:         p.AlertID,
-		EventID:         p.EventID,
-		Action:          p.Action,
-		Message:         p.Message,
-		ServerTime:      time.UnixMilli(p.CreatedAtMs).UTC().Format(time.RFC3339Nano),
-		AutoStopSeconds: p.AutoStopSeconds,
+		Type:       "alarm",
+		AlertID:    p.AlertID,
+		EventID:    p.EventID,
+		Action:     p.Action,
+		Message:    p.Message,
+		ServerTime: time.UnixMilli(p.CreatedAtMs).UTC().Format(time.RFC3339Nano),
 	}
 }