fix: address review comments on admin_script seeding

- Replace TOCTOU race (separate Load+Save) with atomic
  SaveJobTypeConfigIfNotExists on ConfigStore and Plugin
- Replace ineffective polling loop with single GetMaster call using
  30s context timeout, since GetMaster respects context cancellation
- Add unit tests for SaveJobTypeConfigIfNotExists (in-memory + on-disk)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

weed/admin/plugin/config_store.go

@@ -256,6 +256,53 @@ func (s *ConfigStore) SaveJobTypeConfig(config *plugin_pb.PersistedJobTypeConfig
 	return nil
 }
 
+// SaveJobTypeConfigIfNotExists atomically checks whether a config for the
+// given job type already exists and only persists config when none is found.
+// Returns true if the config was saved, false if a config already existed.
+func (s *ConfigStore) SaveJobTypeConfigIfNotExists(config *plugin_pb.PersistedJobTypeConfig) (bool, error) {
+	if config == nil {
+		return false, fmt.Errorf("job type config is nil")
+	}
+	if config.JobType == "" {
+		return false, fmt.Errorf("job type config has empty job_type")
+	}
+	sanitizedJobType, err := sanitizeJobType(config.JobType)
+	if err != nil {
+		return false, err
+	}
+	config.JobType = sanitizedJobType
+
+	clone := proto.Clone(config).(*plugin_pb.PersistedJobTypeConfig)
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if !s.configured {
+		if _, exists := s.memConfigs[config.JobType]; exists {
+			return false, nil
+		}
+		s.memConfigs[config.JobType] = clone
+		return true, nil
+	}
+
+	pbPath := filepath.Join(s.baseDir, jobTypesDirName, config.JobType, configPBFileName)
+	if _, statErr := os.Stat(pbPath); statErr == nil {
+		return false, nil
+	}
+
+	jobTypeDir, err := s.ensureJobTypeDir(config.JobType)
+	if err != nil {
+		return false, err
+	}
+
+	jsonPath := filepath.Join(jobTypeDir, configJSONFileName)
+	if err := writeProtoFiles(clone, filepath.Join(jobTypeDir, configPBFileName), jsonPath); err != nil {
+		return false, fmt.Errorf("save job type config for %s: %w", config.JobType, err)
+	}
+
+	return true, nil
+}
+
 func (s *ConfigStore) LoadJobTypeConfig(jobType string) (*plugin_pb.PersistedJobTypeConfig, error) {
 	if _, err := sanitizeJobType(jobType); err != nil {
 		return nil, err

weed/admin/plugin/config_store_test.go

@@ -208,6 +208,81 @@ func TestConfigStoreMonitorStateRoundTrip(t *testing.T) {
 	}
 }
 
+func TestConfigStoreSaveJobTypeConfigIfNotExists(t *testing.T) {
+	t.Parallel()
+
+	t.Run("in-memory", func(t *testing.T) {
+		t.Parallel()
+		store, err := NewConfigStore("")
+		if err != nil {
+			t.Fatalf("NewConfigStore: %v", err)
+		}
+		testSaveJobTypeConfigIfNotExists(t, store)
+	})
+
+	t.Run("on-disk", func(t *testing.T) {
+		t.Parallel()
+		store, err := NewConfigStore(t.TempDir())
+		if err != nil {
+			t.Fatalf("NewConfigStore: %v", err)
+		}
+		testSaveJobTypeConfigIfNotExists(t, store)
+	})
+}
+
+func testSaveJobTypeConfigIfNotExists(t *testing.T, store *ConfigStore) {
+	t.Helper()
+
+	cfg := &plugin_pb.PersistedJobTypeConfig{
+		JobType:      "admin_script",
+		AdminRuntime: &plugin_pb.AdminRuntimeConfig{Enabled: true},
+	}
+
+	// First call should save.
+	saved, err := store.SaveJobTypeConfigIfNotExists(cfg)
+	if err != nil {
+		t.Fatalf("first SaveJobTypeConfigIfNotExists: %v", err)
+	}
+	if !saved {
+		t.Fatal("expected first call to save the config")
+	}
+
+	// Second call with same job type should not save.
+	saved, err = store.SaveJobTypeConfigIfNotExists(&plugin_pb.PersistedJobTypeConfig{
+		JobType:      "admin_script",
+		AdminRuntime: &plugin_pb.AdminRuntimeConfig{Enabled: false},
+	})
+	if err != nil {
+		t.Fatalf("second SaveJobTypeConfigIfNotExists: %v", err)
+	}
+	if saved {
+		t.Fatal("expected second call to be a no-op")
+	}
+
+	// Verify the original config was preserved.
+	loaded, err := store.LoadJobTypeConfig("admin_script")
+	if err != nil {
+		t.Fatalf("LoadJobTypeConfig: %v", err)
+	}
+	if loaded == nil {
+		t.Fatal("expected config to exist")
+	}
+	if !loaded.AdminRuntime.Enabled {
+		t.Fatal("expected original config (Enabled=true) to be preserved")
+	}
+
+	// Different job type should still save.
+	saved, err = store.SaveJobTypeConfigIfNotExists(&plugin_pb.PersistedJobTypeConfig{
+		JobType: "vacuum",
+	})
+	if err != nil {
+		t.Fatalf("SaveJobTypeConfigIfNotExists for different type: %v", err)
+	}
+	if !saved {
+		t.Fatal("expected save for a different job type")
+	}
+}
+
 func TestConfigStoreJobDetailRoundTrip(t *testing.T) {
 	t.Parallel()
 

weed/admin/plugin/plugin.go

@@ -402,6 +402,19 @@ func (r *Plugin) SaveJobTypeConfig(config *plugin_pb.PersistedJobTypeConfig) err
 	return nil
 }
 
+// SaveJobTypeConfigIfNotExists atomically saves config only if no config
+// exists yet for the job type. Returns true if saved, false if already exists.
+func (r *Plugin) SaveJobTypeConfigIfNotExists(config *plugin_pb.PersistedJobTypeConfig) (bool, error) {
+	saved, err := r.store.SaveJobTypeConfigIfNotExists(config)
+	if err != nil {
+		return false, err
+	}
+	if saved {
+		r.wakeScheduler()
+	}
+	return saved, nil
+}
+
 func (r *Plugin) LoadDescriptor(jobType string) (*plugin_pb.JobTypeDescriptor, error) {
 	return r.store.LoadDescriptor(jobType)
 }