fix(cascade): persist metadata-only first batch when no symbols selected

supernode/adaptors/p2p.go

@@ -134,6 +134,28 @@ func (p *p2pImpl) storeCascadeSymbolsAndData(ctx context.Context, taskID, action
 	totalBytesStored := 0
 	metadataBytesStored := 0
 	firstBatchProcessed := false
+	if len(keys) == 0 && len(metadataFiles) > 0 {
+		logtrace.Info(ctx, "store: batch send (metadata-only)", logtrace.Fields{
+			"taskID":          taskID,
+			"metadata_count":  len(metadataFiles),
+			"metadata_bytes":  metadataBytes,
+			"metadata_mb_est": utils.BytesIntToMB(metadataBytes),
+		})
+		bctx, cancel := context.WithTimeout(ctx, storeBatchContextTimeout)
+		err = p.p2p.StoreBatch(bctx, metadataFiles, P2PDataRaptorQSymbol, taskID)
+		cancel()
+		if err != nil {
+			return totalSymbols, totalAvailable, fmt.Errorf("p2p store batch (metadata-only): %w", err)
+		}
+		logtrace.Info(ctx, "store: batch ok (metadata-only)", logtrace.Fields{
+			"taskID":         taskID,
+			"metadata_count": len(metadataFiles),
+			"metadata_bytes": metadataBytes,
+		})
+		totalBytesStored += metadataBytes
+		metadataBytesStored += metadataBytes
+		firstBatchProcessed = true
+	}
 	for start := 0; start < len(keys); {
 		end := min(start+loadSymbolsBatchSize, len(keys))
 		batch := keys[start:end]

supernode/adaptors/p2p_test.go

@@ -7,7 +7,10 @@ import (
 	"testing"
 
 	"github.com/LumeraProtocol/supernode/v2/p2p"
+	p2pmock "github.com/LumeraProtocol/supernode/v2/p2p/mocks"
+	"github.com/LumeraProtocol/supernode/v2/pkg/codec"
 	"github.com/LumeraProtocol/supernode/v2/pkg/storage/rqstore"
+	"github.com/stretchr/testify/mock"
 	"go.uber.org/mock/gomock"
 )
 
@@ -18,6 +21,14 @@ type clientWithPeersCount struct {
 
 func (c clientWithPeersCount) PeersCount() int { return c.peers }
 
+type p2pClientWithStreamMock struct {
+	*p2pmock.Client
+}
+
+func (c p2pClientWithStreamMock) BatchRetrieveStream(_ context.Context, _ []string, _ int32, _ string, _ func(string, []byte) error, _ ...bool) (int32, error) {
+	return 0, nil
+}
+
 func TestStoreArtefacts_ZeroPeers_ReturnsError(t *testing.T) {
 	svc := NewP2PService(clientWithPeersCount{peers: 0}, nil)
 
@@ -52,3 +63,50 @@ func TestStoreArtefacts_PeersPresent_DoesNotTripGuard(t *testing.T) {
 	}
 }
 
+func TestStoreCascadeSymbolsAndData_MetadataOnlyBatchWhenNoSymbols(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	t.Cleanup(ctrl.Finish)
+
+	store := rqstore.NewMockStore(ctrl)
+	store.EXPECT().StoreSymbolDirectory("task", "").Return(nil)
+	store.EXPECT().UpdateIsFirstBatchStored("task").Return(nil)
+
+	metadata := [][]byte{[]byte("index-bytes"), []byte("layout-bytes")}
+	baseClient := p2pmock.NewClient(t)
+	baseClient.On("StoreBatch", mock.Anything, metadata, P2PDataRaptorQSymbol, "task").Return(nil).Once()
+
+	svc := &p2pImpl{p2p: p2pClientWithStreamMock{Client: baseClient}, rqStore: store}
+	stored, total, err := svc.storeCascadeSymbolsAndData(context.Background(), "task", "action", "", metadata, codec.Layout{Blocks: []codec.Block{{BlockID: 0}}})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if stored != 0 {
+		t.Fatalf("expected 0 stored symbols, got %d", stored)
+	}
+	if total != 0 {
+		t.Fatalf("expected 0 total symbols, got %d", total)
+	}
+}
+
+func TestStoreCascadeSymbolsAndData_MetadataOnlyBatchFailureSkipsFirstBatchFlag(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	t.Cleanup(ctrl.Finish)
+
+	store := rqstore.NewMockStore(ctrl)
+	store.EXPECT().StoreSymbolDirectory("task", "").Return(nil)
+	store.EXPECT().UpdateIsFirstBatchStored("task").Times(0)
+
+	metadata := [][]byte{[]byte("index-bytes")}
+	baseClient := p2pmock.NewClient(t)
+	baseClient.On("StoreBatch", mock.Anything, metadata, P2PDataRaptorQSymbol, "task").Return(errors.New("p2p down")).Once()
+
+	svc := &p2pImpl{p2p: p2pClientWithStreamMock{Client: baseClient}, rqStore: store}
+	_, _, err := svc.storeCascadeSymbolsAndData(context.Background(), "task", "action", "", metadata, codec.Layout{Blocks: []codec.Block{{BlockID: 0}}})
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), "metadata-only") {
+		t.Fatalf("expected metadata-only path error, got: %v", err)
+	}
+}
+