fix(model): do not treat no-op system task state writes as lock loss (#7135)

model/system_task.go

@@ -322,7 +322,23 @@ func UpdateSystemTaskState(taskID string, lockedBy string, state any) error {
 	if result.Error != nil {
 		return result.Error
 	}
-	if result.RowsAffected == 0 {
+	if result.RowsAffected > 0 {
+		return nil
+	}
+	// MySQL counts changed rows, not matched rows. A no-op persist of the same
+	// state in the same second therefore returns RowsAffected == 0 even while
+	// the lease is still held. Confirm the lock before treating this as loss.
+	// Reuse `now` from the UPDATE so a clock tick cannot reintroduce false
+	// lock-loss; a lease that expires during the write is caught by the next heartbeat.
+	var held int64
+	err = DB.Model(&SystemTask{}).
+		Where("task_id = ? AND status = ? AND locked_by = ?", taskID, SystemTaskStatusRunning, lockedBy).
+		Where("EXISTS (SELECT 1 FROM system_task_locks WHERE system_task_locks.task_id = system_tasks.task_id AND system_task_locks.locked_by = ? AND system_task_locks.locked_until >= ?)", lockedBy, now).
+		Count(&held).Error
+	if err != nil {
+		return err
+	}
+	if held == 0 {
 		return ErrSystemTaskLockLost
 	}
 	return nil

model/system_task_test.go

@@ -350,3 +350,34 @@ func TestSystemTaskUpdatesRequireUnexpiredLock(t *testing.T) {
 	assert.Equal(t, SystemTaskStatusRunning, reloaded.Status)
 	assert.Empty(t, reloaded.State)
 }
+
+func TestUpdateSystemTaskStateIdenticalPayloadDoesNotLoseLock(t *testing.T) {
+	// SQLite reports matched rows for unchanged UPDATEs, so this case passed
+	// even before the fix. The MySQL regression is covered by
+	// TestUpdateSystemTaskStateIdenticalPayloadDoesNotLoseLockConfiguredDatabases.
+	truncateTables(t)
+	runUpdateSystemTaskStateIdenticalPayloadKeepsLock(t, SystemTaskTypeLogCleanup)
+}
+
+func runUpdateSystemTaskStateIdenticalPayloadKeepsLock(t *testing.T, taskType string) {
+	t.Helper()
+	// Two persists in the same second so MySQL's unchanged-row UPDATE returns 0.
+
+	task, err := CreateSystemTask(taskType, nil, nil)
+	require.NoError(t, err)
+
+	runnerID := "runner-a"
+	_, claimed, err := ClaimSystemTask(task.ID, taskType, runnerID, common.GetTimestamp()+60)
+	require.NoError(t, err)
+	require.True(t, claimed)
+
+	state := testSystemTaskState{Total: 10, Processed: 10, Progress: 100, Remaining: 0}
+	require.NoError(t, UpdateSystemTaskState(task.TaskID, runnerID, state))
+	require.NoError(t, UpdateSystemTaskState(task.TaskID, runnerID, state), "identical state persist must not be treated as lock loss")
+
+	require.NoError(t, FinishSystemTask(task.TaskID, runnerID, SystemTaskStatusSucceeded, map[string]int64{"deleted_count": 10}, ""))
+	finished, err := GetSystemTaskByTaskID(task.TaskID)
+	require.NoError(t, err)
+	require.NotNil(t, finished)
+	assert.Equal(t, SystemTaskStatusSucceeded, finished.Status)
+}