Graph clone tests accept extra nodes with duplicate IDs #381

Observed behavior

The JavaScript tests for Sandbox Topology Replica (clone-graph) accept a returned graph containing an extra reachable node with the same ID as another node. A correct clone and the invalid clone below both pass 5/5 cases at revision 0fecc3371614adb87c0fa840a9e4b52b1e29154d.

For the two-node input 1 <-> 2, this defect can produce three distinct objects: 1a -> 2 -> 1b -> 2, where 1a and 1b both have val === 1. This is not a copy of the original two-node graph, but the judge serializes it as [[2],[1]].

Expected behavior

Different reachable objects sharing one node ID should fail. A correct deep copy should continue to pass, including one whose neighbors appear in a different order.

Reproduction

1. Serve the checkout's web/ directory locally and open a page on that origin.
2. Run the following in the browser console. This isolates the existing JavaScript runner without requiring LiveKit or Gemini credentials.

const { runBrowserTests } = await import("/runners.js");

function replicateTopology(node) {
  const copies = new Map();
  function clone(current) {
    if (!current) return null;
    if (copies.has(current)) return copies.get(current);
    const copy = new Node(current.val);
    copies.set(current, copy);
    copy.neighbors = current.neighbors.map(clone);
    return copy;
  }
  const root = clone(node);
  if (root && root.neighbors.length) {
    const first = root.neighbors[0];
    const duplicate = new Node(root.val, root.neighbors.slice());
    first.neighbors = first.neighbors.map(
      neighbor => neighbor === root ? duplicate : neighbor
    );
  }
  return root;
}

const result = await runBrowserTests(
  "sandbox-topology-replica",
  replicateTopology.toString(),
  "javascript"
);
console.log(result.passed, result.total, result.cases);

3. Observe 5 5, with every case marked as passing.
4. Remove the block that creates duplicate and repeat. The correct clone also passes 5/5.

CodeTrial version

Source checkout: 0fecc3371614adb87c0fa840a9e4b52b1e29154d. The reproduction used the checkout's browser modules served by a local static server, not a prebuilt CodeTrial binary or a live interview. The Rust source build has not completed.

Environment

Environment: Windows, Chrome 155.0.8059.85, JavaScript, Sandbox Topology Replica.

Sanitized evidence

Initial analysis

graphToAdjacency in web/runners.js records visited nodes in byValue, keyed by current.val. A different object with an already visited value is silently skipped. The adjacency list therefore loses the distinction between those objects before answer comparison.

The problem contract requires a corresponding deep copy with distinct IDs and the same links. Python, C++, and Java contain similar value-keyed traversal, but I have only executed the JavaScript reproduction.

Proposed scope and verification

Detect distinct returned objects that share an ID before adjacency serialization. Preserve rejection of original nodes and order-independent neighbor comparison. Add executable regression coverage that rejects the invalid clone, accepts the correct clone, and accepts reordered neighbors. Confirm the affected languages before expanding the implementation.

Related: #360 and PR #376 address neighbor ordering in C; #332 and PR #333 address a C struct field name. Neither addresses duplicate node identities.

Public data confirmation

• This report contains only synthetic examples and excludes credentials, session tokens, candidate recordings, and personal interview content.

Public data confirmation

• I removed credentials, session tokens, candidate recordings, and personal interview content from this public report.