perf: task directory is created lazily

Author: voocel

internal/cron/cron.go

@@ -338,15 +338,27 @@ func (s *Store) scheduleDurableWrite() {
 // flushDurable serializes under RLock and writes outside the lock.
 func (s *Store) flushDurable() {
 	s.mu.RLock()
+	jobCount := len(s.durableJobs)
 	data := s.marshalDurableJobs()
 	dir := s.configDir
 	s.mu.RUnlock()
 
 	if dir == "" || data == nil {
 		return
 	}
+	filePath := filepath.Join(dir, scheduledTasksFile)
+	// Skip persisting an empty job list when no file exists yet: StopWriter
+	// calls this unconditionally on shutdown, and without this guard every
+	// session that never scheduled a cron task would leave behind an empty
+	// <sessionID>/scheduled_tasks.json. When the file already exists the
+	// empty list is still written so that deleting the last job persists.
+	if jobCount == 0 {
+		if _, err := os.Stat(filePath); os.IsNotExist(err) {
+			return
+		}
+	}
 	_ = os.MkdirAll(dir, 0o755)
-	_ = os.WriteFile(filepath.Join(dir, scheduledTasksFile), data, 0o644)
+	_ = os.WriteFile(filePath, data, 0o644)
 }
 
 // marshalDurableJobs serializes durable jobs to JSON. Must hold at least RLock.

internal/storage/task_store.go

@@ -375,12 +375,10 @@ func taskAppendUnique(base []string, vals ...string) []string {
 
 const taskHighWaterMarkFile = ".highwatermark"
 
-// SetDir enables file persistence. It creates the directory if needed and
-// loads any existing tasks from disk. Call before the store is used.
+// SetDir enables file persistence. The directory is created lazily on the
+// first write (persistLocked / writeHighWaterMarkLocked) — sessions that
+// never create a task leave nothing behind on disk.
 func (s *TaskStore) SetDir(dir string) error {
-	if err := os.MkdirAll(dir, 0o755); err != nil {
-		return fmt.Errorf("create task dir: %w", err)
-	}
 	s.mu.Lock()
 	s.dir = dir
 	s.mu.Unlock()
@@ -390,6 +388,9 @@ func (s *TaskStore) SetDir(dir string) error {
 func (s *TaskStore) loadFromDir() error {
 	entries, err := os.ReadDir(s.dir)
 	if err != nil {
+		if os.IsNotExist(err) {
+			return nil // dir not created yet — no prior tasks to load
+		}
 		return fmt.Errorf("read task dir: %w", err)
 	}