tapdb: fix incorrect asset ID for grouped assets

It doesn't make sense to have the asset ID set for grouped assets in the
multiverse or universe roots tables. The asset ID would only really
point to the very first asset.

tapdb/sqlc/migrations/000010_multiverse_tree.up.sql

@@ -49,6 +49,12 @@ WHERE EXISTS (
     SELECT 1 FROM mssmt_roots WHERE namespace = 'multiverse-transfer'
 );
 
+-- Before we turn the existing universe_roots into multiverse_leaves, we need to
+-- fix a bug in the data where the asset ID was set for grouped assets.
+UPDATE universe_roots
+SET asset_id = NULL
+WHERE group_key IS NOT NULL;
+
 -- And now we create the multiverse_leaves entries for the multiverse roots.
 -- This is a no-op if the multiverse root doesn't exist yet.
 INSERT INTO multiverse_leaves (

tapdb/universe.go

@@ -373,9 +373,11 @@ func universeUpsertProofLeaf(ctx context.Context, dbTx BaseUniverseStore,
 		return nil, nil, err
 	}
 
-	var groupKeyBytes []byte
+	var groupKeyBytes, assetIDBytes []byte
 	if id.GroupKey != nil {
 		groupKeyBytes = schnorr.SerializePubKey(id.GroupKey)
+	} else {
+		assetIDBytes = id.AssetID[:]
 	}
 
 	mintingPointBytes, err := encodeOutpoint(key.OutPoint)
@@ -405,7 +407,7 @@ func universeUpsertProofLeaf(ctx context.Context, dbTx BaseUniverseStore,
 	// root ID that we'll use to insert the universe leaf overlay.
 	universeRootID, err := dbTx.UpsertUniverseRoot(ctx, NewUniverseRoot{
 		NamespaceRoot: namespace,
-		AssetID:       fn.ByteSlice(leaf.ID()),
+		AssetID:       assetIDBytes,
 		GroupKey:      groupKeyBytes,
 		ProofType:     id.ProofType.String(),
 	})