fix global mutation issue

Author: tudor-malene

encoding.go

@@ -145,7 +145,8 @@ func parseEoAccountNode(serialized []byte, depth byte) (VerkleNode, error) {
 	if err := ln.c1.SetBytesUncompressed(serialized[leafStemOffset+StemSize:leafStemOffset+StemSize+banderwagon.UncompressedSize], true); err != nil {
 		return nil, fmt.Errorf("error setting leaf C1 commitment: %w", err)
 	}
-	ln.c2 = &banderwagon.Identity
+	ln.c2 = new(Point)
+	*ln.c2 = banderwagon.Identity
 	ln.commitment = new(Point)
 	if err := ln.commitment.SetBytesUncompressed(serialized[leafStemOffset+StemSize+banderwagon.UncompressedSize:leafStemOffset+StemSize+banderwagon.UncompressedSize*2], true); err != nil {
 		return nil, fmt.Errorf("error setting leaf root commitment: %w", err)
@@ -171,13 +172,15 @@ func parseSingleSlotNode(serialized []byte, depth byte) (VerkleNode, error) {
 		if err := ln.c1.SetBytesUncompressed(cnCommBytes, true); err != nil {
 			return nil, fmt.Errorf("error setting leaf C1 commitment: %w", err)
 		}
-		ln.c2 = &banderwagon.Identity
+		ln.c2 = new(Point)
+		*ln.c2 = banderwagon.Identity
 	} else {
 		ln.c2 = new(Point)
 		if err := ln.c2.SetBytesUncompressed(cnCommBytes, true); err != nil {
 			return nil, fmt.Errorf("error setting leaf C2 commitment: %w", err)
 		}
-		ln.c1 = &banderwagon.Identity
+		ln.c1 = new(Point)
+		*ln.c1 = banderwagon.Identity
 	}
 	ln.commitment = new(Point)
 	if err := ln.commitment.SetBytesUncompressed(rootCommBytes, true); err != nil {

encoding_test.go

@@ -191,3 +191,43 @@ func TestParseNodeSingleSlot(t *testing.T) {
 		t.Fatalf("invalid commitment, got %x, expected %x", lnd.commitment, ln.commitment)
 	}
 }
+
+func TestLeaf_FirstC2Write_DoesNotMutate_GlobalIdentity(t *testing.T) {
+	// Build a leaf with exactly one value in c1 (suffix 7), so Serialize() picks single-slot encoding.
+	values := make([][]byte, NodeWidth)
+	values[7] = word32(0x11)
+
+	ln, err := NewLeafNode(ffx32KeyTest[:StemSize], values)
+	if err != nil {
+		t.Fatalf("NewLeafNode: %v", err)
+	}
+	ser, err := ln.Serialize()
+	if err != nil {
+		t.Fatalf("Serialize: %v", err)
+	}
+	if got := ser[0]; got != singleSlotType {
+		t.Fatalf("expected single-slot encoding, got type=%d", got)
+	}
+
+	node, err := ParseNode(ser, 0)
+	if err != nil {
+		t.Fatalf("ParseNode: %v", err)
+	}
+	leaf, ok := node.(*LeafNode)
+	if !ok {
+		t.Fatalf("expected *LeafNode, got %T", node)
+	}
+
+	// Snapshot global identity (value copy) to compare later.
+	idBefore := banderwagon.Identity
+
+	// First write into c2 (suffix 128). This must NOT mutate banderwagon.Identity.
+	val := word32(0x03)
+	if err := leaf.updateCn(128, val, leaf.c2); err != nil {
+		t.Fatalf("updateCn(c2): %v", err)
+	}
+
+	if idBefore != banderwagon.Identity {
+		t.Fatalf("BUG: first c2 write mutated global banderwagon.Identity")
+	}
+}