fix(downloader): make aria2 reset idempotent

cmd/internal/engine/aria2.go

@@ -144,11 +144,18 @@ func (a Aria2) ResetTask(ctx context.Context, task client.DownloadTask) error {
 		if !aria2StatusBelongsToTask(status, taskDir, aria2TaskGID(task.ID)) {
 			continue
 		}
-		if err := aria.ForceRemove(status.GID); err != nil {
-			resetErrs = append(resetErrs, fmt.Errorf("force remove aria2 gid %s: %w", status.GID, err))
+		removeActive, removeResult := aria2ResetOperations(status)
+		if removeActive {
+			err := aria.ForceRemove(status.GID)
+			if err != nil && !isAria2DownloadNotFound(err) {
+				resetErrs = append(resetErrs, fmt.Errorf("force remove aria2 gid %s: %w", status.GID, err))
+			}
 		}
-		if err := aria.RemoveDownloadResult(status.GID); err != nil {
-			resetErrs = append(resetErrs, fmt.Errorf("remove aria2 result %s: %w", status.GID, err))
+		if removeResult {
+			err := aria.RemoveDownloadResult(status.GID)
+			if err != nil && !isAria2DownloadNotFound(err) {
+				resetErrs = append(resetErrs, fmt.Errorf("remove aria2 result %s: %w", status.GID, err))
+			}
 		}
 	}
 	if err := os.RemoveAll(taskDir); err != nil {
@@ -157,6 +164,25 @@ func (a Aria2) ResetTask(ctx context.Context, task client.DownloadTask) error {
 	return errors.Join(resetErrs...)
 }
 
+func aria2ResetOperations(status arigo.Status) (removeActive bool, removeResult bool) {
+	switch string(status.Status) {
+	case string(arigo.StatusCompleted), string(arigo.StatusError), string(arigo.StatusRemoved), "complete":
+		return false, true
+	case string(arigo.StatusActive), string(arigo.StatusWaiting), string(arigo.StatusPaused):
+		return true, true
+	default:
+		return true, true
+	}
+}
+
+func isAria2DownloadNotFound(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := strings.ToLower(err.Error())
+	return strings.Contains(msg, "download") && strings.Contains(msg, "not found")
+}
+
 func (a Aria2) SaveSession(ctx context.Context) error {
 	client, err := a.client(ctx)
 	if err != nil {

cmd/internal/engine/engine_test.go

@@ -150,6 +150,49 @@ func TestAria2StartArgsForceSaveCompletedSeeds(t *testing.T) {
 	}
 }
 
+func TestAria2ResetOperations(t *testing.T) {
+	tests := []struct {
+		name             string
+		status           arigo.DownloadStatus
+		wantRemoveActive bool
+		wantRemoveResult bool
+	}{
+		{name: "active", status: arigo.StatusActive, wantRemoveActive: true, wantRemoveResult: true},
+		{name: "waiting", status: arigo.StatusWaiting, wantRemoveActive: true, wantRemoveResult: true},
+		{name: "paused", status: arigo.StatusPaused, wantRemoveActive: true, wantRemoveResult: true},
+		{name: "completed", status: arigo.StatusCompleted, wantRemoveActive: false, wantRemoveResult: true},
+		{name: "error", status: arigo.StatusError, wantRemoveActive: false, wantRemoveResult: true},
+		{name: "removed", status: arigo.StatusRemoved, wantRemoveActive: false, wantRemoveResult: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			removeActive, removeResult := aria2ResetOperations(arigo.Status{Status: tt.status})
+			if removeActive != tt.wantRemoveActive || removeResult != tt.wantRemoveResult {
+				t.Fatalf(
+					"expected removeActive=%v removeResult=%v, got removeActive=%v removeResult=%v",
+					tt.wantRemoveActive,
+					tt.wantRemoveResult,
+					removeActive,
+					removeResult,
+				)
+			}
+		})
+	}
+}
+
+func TestIsAria2DownloadNotFound(t *testing.T) {
+	if !isAria2DownloadNotFound(errors.New("Active Download not found for GID#b384ccaa7eae88da")) {
+		t.Fatal("expected aria2 active download not found to be ignored during reset")
+	}
+	if !isAria2DownloadNotFound(errors.New("Download result not found for GID#b384ccaa7eae88da")) {
+		t.Fatal("expected aria2 download result not found to be ignored during reset")
+	}
+	if isAria2DownloadNotFound(errors.New("aria2 download ended with status error")) {
+		t.Fatal("expected ordinary aria2 download errors to stay visible")
+	}
+}
+
 func TestHTTPDownloadResumesExistingFile(t *testing.T) {
 	var rangeHeader string
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {