proof: add STXO inclusion proofs for non-splits

Co-authored-by: Gijs van Dam <[email protected]>

Author: 2 people

proof/append.go

@@ -160,6 +160,41 @@ func CreateTransitionProof(prevOut wire.OutPoint,
 		TapSiblingPreimage: params.TapscriptSibling,
 	}
 
+	if proof.Asset.IsTransferRoot() {
+		stxoInclusionProofs := make(
+			map[asset.SerializedKey]commitment.Proof,
+			len(proof.Asset.PrevWitnesses),
+		)
+		for _, wit := range proof.Asset.PrevWitnesses {
+			spentAsset, err := asset.MakeSpentAsset(wit)
+			if err != nil {
+				return nil, fmt.Errorf("error creating "+
+					"altLeaf: %w", err)
+			}
+
+			// Generate an STXO inclusion proof for each prev
+			// witness.
+			_, stxoProof, err := params.TaprootAssetRoot.Proof(
+				asset.EmptyGenesisID,
+				spentAsset.AssetCommitmentKey(),
+			)
+			if err != nil {
+				return nil, err
+			}
+			keySerialized := asset.ToSerialized(
+				spentAsset.ScriptKey.PubKey,
+			)
+			stxoInclusionProofs[keySerialized] = *stxoProof
+		}
+
+		if len(stxoInclusionProofs) == 0 {
+			return nil, fmt.Errorf("no stxo inclusion proofs")
+		}
+
+		proof.InclusionProof.CommitmentProof.STXOProofs =
+			stxoInclusionProofs
+	}
+
 	// If the asset is a split asset, we also need to generate MS-SMT
 	// inclusion proofs that prove the existence of the split root asset.
 	if proof.Asset.HasSplitCommitmentWitness() {