Update app.py

app.py

@@ -313,17 +313,15 @@ def merkle_root_and_proofs(leaves: List[bytes]) -> Tuple[bytes, List[List[Dict[s
       - "L" means sibling was on the left (sib || cur)
       - "R" means sibling was on the right (cur || sib)
 
-    Handles odd leaf counts by duplicating the last node at that level.
+    Odd leaf counts are handled by duplicating the last node.
+    IMPORTANT: duplicated nodes add exactly ONE proof step (not two).
     """
     n = len(leaves)
     if n == 0:
         return _h(b"\x00"), []
 
-    # initial leaf hashes
     level_hashes = [merkle_leaf(x) for x in leaves]
     proofs: List[List[Dict[str, str]]] = [[] for _ in range(n)]
-
-    # track which original leaf indices are covered by each node
     level_sets: List[List[int]] = [[i] for i in range(n)]
 
     while len(level_hashes) > 1:
@@ -338,23 +336,30 @@ def merkle_root_and_proofs(leaves: List[bytes]) -> Tuple[bytes, List[List[Dict[s
             if j + 1 < len(level_hashes):
                 right = level_hashes[j + 1]
                 right_set = level_sets[j + 1]
+
+                # normal pair: add sibling to each side
+                right_hex = right.hex()
+                left_hex = left.hex()
+
+                for idx in left_set:
+                    proofs[idx].append({"dir": "R", "hash_hex": right_hex})
+                for idx in right_set:
+                    proofs[idx].append({"dir": "L", "hash_hex": left_hex})
+
+                parent = merkle_node(left, right)
+                next_hashes.append(parent)
+                next_sets.append(left_set + right_set)
+
             else:
-                # duplicate last node when odd
-                right = left
-                right_set = left_set
-
-            # append sibling step to ALL leaves under each side
-            right_hex = right.hex()
-            left_hex = left.hex()
-
-            for idx in left_set:
-                proofs[idx].append({"dir": "R", "hash_hex": right_hex})
-            for idx in right_set:
-                proofs[idx].append({"dir": "L", "hash_hex": left_hex})
-
-            parent = merkle_node(left, right)
-            next_hashes.append(parent)
-            next_sets.append(left_set + right_set)
+                # odd leaf: duplicate last node
+                # add exactly ONE step: sibling is itself
+                left_hex = left.hex()
+                for idx in left_set:
+                    proofs[idx].append({"dir": "R", "hash_hex": left_hex})
+
+                parent = merkle_node(left, left)
+                next_hashes.append(parent)
+                next_sets.append(left_set)
 
             j += 2