fix(kuma-sync): create when the previous monitor ID belongs to another owner

After a Kuma database loss or restore, IDs restart and a resource's
status.monitorID can point at a monitor that now carries another
resource's ownership tag. That proves our monitor is gone, so the
controller creates a new one instead of parking at NotOwned forever.
Only an untagged monitor at the previous ID still blocks the create
(tag removed by hand), as before.

Residual Important finding from the kuma-sync final review.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ci/images/kuma-sync/internal/controller/kumamonitor_controller.go

@@ -133,18 +133,19 @@ func (r *Reconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Resu
 	var id int64
 	if res.mon == nil {
 		// The monitor this resource synced before may have lost its tag; a
-		// second one would then sit beside it.
+		// second one would then sit beside it. An ID now carrying another
+		// owner's key was reused by Kuma, so ours is gone.
 		if prev := km.Status.MonitorID; prev != 0 {
 			found, key, err := r.Kuma.Probe(ctx, prev)
 			switch {
 			case err != nil:
 				return r.fail(ctx, km, &failure{ReasonKumaUnavailable, msgKumaUnavailable, err})
-			case found && key != desired.OwnerKey:
+			case found && key == "":
 				log.FromContext(ctx).Error(nil, "previous monitor exists without our ownership tag, not creating another",
 					"ownerKey", desired.OwnerKey, "monitorID", prev, "tagValue", key)
 				err := r.setReady(ctx, km, metav1.ConditionFalse, ReasonNotOwned, msgNotOwned, nil)
 				return ctrl.Result{RequeueAfter: r.resync()}, err
-			case found:
+			case found && key == desired.OwnerKey:
 				return r.fail(ctx, km, &failure{ReasonKumaUnavailable, msgKumaUnavailable,
 					fmt.Errorf("monitor %d carries our key but is missing from the owned list", prev)})
 			}

ci/images/kuma-sync/internal/controller/kumamonitor_controller_test.go

@@ -428,7 +428,7 @@ func TestReconcileRefusesCreateBesideUntaggedPrevious(t *testing.T) {
 	}
 }
 
-func TestReconcileRefusesCreateBesideOtherOwnersMonitor(t *testing.T) {
+func TestReconcileCreatesWhenPreviousIDReusedByOtherOwner(t *testing.T) {
 	e := newEnv(t, withPreviousMonitor(1))
 	if _, err := e.kuma.Create(t.Context(), kumaclient.Monitor{Name: "x", OwnerKey: "default/other"}); err != nil {
 		t.Fatal(err)
@@ -436,12 +436,15 @@ func TestReconcileRefusesCreateBesideOtherOwnersMonitor(t *testing.T) {
 	if _, err := e.reconcile(t, "a"); err != nil {
 		t.Fatal(err)
 	}
-	if e.cnt.creates != 0 {
-		t.Errorf("creates = %d, want 0", e.cnt.creates)
+	if e.cnt.creates != 1 {
+		t.Errorf("creates = %d, want 1", e.cnt.creates)
 	}
-	if c := ready(t, e.get(t, "a")); c.Reason != ReasonNotOwned {
+	if c := ready(t, e.get(t, "a")); c.Reason != ReasonSynced {
 		t.Errorf("Ready = %+v", c)
 	}
+	if m := e.kuma.Get(1); m == nil || m.OwnerKey != "default/other" {
+		t.Errorf("other owner's monitor 1 = %+v, want untouched", m)
+	}
 }
 
 func TestReconcileCreatesWhenPreviousMonitorIsGone(t *testing.T) {