fix: harden per-item processing tracking in tasks

Use the resource fingerprint as the dedup key on insert and delete.
Check and set processing entries atomically instead of TOCTOU.
Count only successful downloads.

core/tasks/parsed/execute.go

@@ -30,21 +30,20 @@ func (t *Task) Execute(ctx context.Context) error {
 	eg.SetLimit(config.C().Workers)
 	for _, resource := range t.item.Resources {
 		eg.Go(func() error {
-			t.processingMu.RLock()
-			if t.processing[resource.ID()] != nil {
-				return fmt.Errorf("resource %s is already being processed", resource.ID())
-			}
-			t.processingMu.RUnlock()
+			resourceID := resource.ID()
 			t.processingMu.Lock()
-			t.processing[resource.ID()] = &resource
+			if t.processing[resourceID] != nil {
+				t.processingMu.Unlock()
+				return fmt.Errorf("resource %s is already being processed", resourceID)
+			}
+			t.processing[resourceID] = &resource
 			t.processingMu.Unlock()
 			defer func() {
 				t.processingMu.Lock()
-				delete(t.processing, resource.URL)
+				delete(t.processing, resourceID)
 				t.processingMu.Unlock()
 			}()
 			err := t.processResource(gctx, resource)
-			t.downloaded.Add(1)
 			if errors.Is(err, context.Canceled) {
 				logger.Debug("Resource processing canceled")
 				return err
@@ -53,6 +52,7 @@ func (t *Task) Execute(ctx context.Context) error {
 				logger.Errorf("Error processing resource %s: %v", resource.URL, err)
 				return fmt.Errorf("failed to process resource %s: %w", resource.URL, err)
 			}
+			t.downloaded.Add(1)
 			return nil
 		})
 	}

core/tasks/parsed/task.go

@@ -33,7 +33,6 @@ type Task struct {
 	downloadedBytes atomic.Int64 // downloaded bytes count
 	processing      map[string]ResourceInfo
 	processingMu    sync.RWMutex
-	failed          map[string]error // [TODO] errors for each resource
 }
 
 // Title implements core.Exectable.
@@ -84,6 +83,5 @@ func NewTask(
 		progress:        progressTracker,
 		processing:      make(map[string]ResourceInfo),
 		processingMu:    sync.RWMutex{},
-		failed:          make(map[string]error),
 	}
 }