feat: publish standalone worker

Separate worker packaging and service lifecycle from the control plane.

app/models/maintenance_notifications.go

@@ -0,0 +1,44 @@
+package models
+
+import (
+	"fmt"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+const maintenanceStartNotificationPrefix = "maintenance:%d:start:"
+
+// MaintenanceStartNotificationKey uniquely identifies one contact's warning
+// for one schedule revision and occurrence. Updated windows get a new revision
+// while concurrent scheduler replicas share the same key.
+func MaintenanceStartNotificationKey(maintenanceID int64, revision, startsAt time.Time, timezone string, notificationID, contactID int64) string {
+	loc, err := time.LoadLocation(timezone)
+	if err != nil || timezone == "SAME_AS_SERVER" || timezone == "" {
+		loc = time.UTC
+	}
+	// A fall-back hour can have two UTC instants for one wall-clock occurrence.
+	// Warnings are once per civil occurrence, matching the recurrence editor.
+	civilOccurrence := startsAt.In(loc).Format("200601021504")
+	return fmt.Sprintf("maintenance:%d:start:%d:%s:notification:%d:contact:%d", maintenanceID, revision.UnixNano(), civilOccurrence, notificationID, contactID)
+}
+
+// CancelMaintenanceStartNotificationsTx prevents queued warnings from being
+// delivered after an operator pauses, changes, or deletes the maintenance.
+// Leased work may already be executing and cannot be recalled from a worker.
+func CancelMaintenanceStartNotificationsTx(tx *gorm.DB, maintenanceID int64, reason string) error {
+	prefix := fmt.Sprintf(maintenanceStartNotificationPrefix, maintenanceID) + "%"
+	var tasks []Task
+	if err := tx.Clauses(SkipLockedClause).Where("idempotency_key LIKE ? AND state IN ?", prefix, []string{TaskStateQueued, TaskStateFailedRetry}).Find(&tasks).Error; err != nil {
+		return err
+	}
+	for i := range tasks {
+		if err := tx.Model(&Task{}).Where("id = ? AND state IN ?", tasks[i].ID, []string{TaskStateQueued, TaskStateFailedRetry}).Updates(map[string]any{"state": TaskStateDead, "last_error": "canceled: " + reason, "payload": []byte(`{}`), "lease_owner": "", "lease_token": "", "lease_expires_at": nil}).Error; err != nil {
+			return err
+		}
+		if err := FinalizeNotificationTaskTx(tx, &tasks[i], "canceled", "canceled: "+reason); err != nil {
+			return err
+		}
+	}
+	return nil
+}