test: Add taskHeap.Less tiebreaker test case

When tasks have identical NextRun and Priority, the Less function
falls back to comparing InstanceName alphabetically. Add test to
cover this edge case branch, improving Less coverage to 100%.

internal/monitoring/task_queue_test.go

@@ -485,6 +485,51 @@ func TestTaskQueue_Upsert(t *testing.T) {
 
 		verifyHeapInvariant(t, queue)
 	})
+
+	t.Run("upsert with same time and priority - uses instance name for tiebreak", func(t *testing.T) {
+		queue := NewTaskQueue()
+		now := time.Now()
+		sameTime := now.Add(10 * time.Second)
+
+		// Same NextRun, same priorities - should use InstanceName for tiebreak
+		tasks := []ScheduledTask{
+			{
+				InstanceName: "pve-zebra",
+				InstanceType: InstanceTypePVE,
+				NextRun:      sameTime,
+				Interval:     30 * time.Second,
+				Priority:     1.0,
+			},
+			{
+				InstanceName: "pve-alpha",
+				InstanceType: InstanceTypePVE,
+				NextRun:      sameTime,
+				Interval:     30 * time.Second,
+				Priority:     1.0,
+			},
+			{
+				InstanceName: "pve-middle",
+				InstanceType: InstanceTypePVE,
+				NextRun:      sameTime,
+				Interval:     30 * time.Second,
+				Priority:     1.0,
+			},
+		}
+
+		for _, task := range tasks {
+			queue.Upsert(task)
+		}
+
+		// When NextRun and Priority are equal, alphabetically earlier name should be first
+		queue.mu.Lock()
+		root := queue.heap[0]
+		if root.task.InstanceName != "pve-alpha" {
+			t.Errorf("heap root = %s, want pve-alpha (alphabetically first when time and priority equal)", root.task.InstanceName)
+		}
+		queue.mu.Unlock()
+
+		verifyHeapInvariant(t, queue)
+	})
 }
 
 func TestTaskQueue_Remove(t *testing.T) {