fix(graph): stop leaking edges to excluded neighbors

CHANGELOG.md

@@ -7,6 +7,12 @@ All notable changes to vouch are documented here. Format follows
 ## [Unreleased]
 
 ### Fixed
+- `graph.find_neighbors()` no longer leaks edges to excluded neighbors.
+  superseded/archived/redacted claims and missing nodes were already filtered
+  out of the returned `nodes` list, but the edge pointing at them was still
+  included -- `kb.neighbors` (mcp, jsonl, and cli surfaces all share this
+  code path) could hand back an edge whose `target` referenced a claim id
+  the response itself said didn't exist.
 - `lifecycle.contradict()` no longer lets a claim contradict itself. calling
   it with the same claim id on both sides previously wrote a self-loop
   `contradicts` reference and flipped the claim to `contested` with no

src/vouch/graph.py

@@ -176,6 +176,23 @@ def find_neighbors(
         for current in frontier:
             for edge in _edges_from_node(store, current, rel_types=rel_filter):
                 other = edge.target if edge.source == current else edge.source
+                if other not in visited:
+                    try:
+                        kind = _node_kind(store, other)
+                    except ArtifactNotFoundError:
+                        continue
+                    if not _neighbor_ok(store, other, kind):
+                        continue
+                    visited.add(other)
+                    next_frontier.append(other)
+                    nodes.append({
+                        "id": other,
+                        "kind": kind,
+                        "distance": dist,
+                        "via": current,
+                        "relation": edge.relation,
+                        "summary": _summary_for(store, kind, other),
+                    })
                 ekey = (edge.source, edge.target, edge.relation)
                 if ekey not in seen_edges:
                     seen_edges.add(ekey)
@@ -185,24 +202,6 @@ def find_neighbors(
                         "relation": edge.relation,
                         "relation_id": edge.relation_id,
                     })
-                if other in visited:
-                    continue
-                try:
-                    kind = _node_kind(store, other)
-                except ArtifactNotFoundError:
-                    continue
-                if not _neighbor_ok(store, other, kind):
-                    continue
-                visited.add(other)
-                next_frontier.append(other)
-                nodes.append({
-                    "id": other,
-                    "kind": kind,
-                    "distance": dist,
-                    "via": current,
-                    "relation": edge.relation,
-                    "summary": _summary_for(store, kind, other),
-                })
                 if len(nodes) >= max_nodes:
                     break
             if len(nodes) >= max_nodes:

tests/test_graph.py

@@ -93,6 +93,10 @@ def test_find_neighbors_excludes_superseded_claims(store: KBStore) -> None:
     result = graph.find_neighbors(store, "new", depth=1)
     assert {n["id"] for n in result["nodes"]} == set()
     assert "old" not in {n["id"] for n in result["nodes"]}
+    # the edge to the excluded neighbor must not leak either -- a client
+    # that trusts `nodes` as the visible set would otherwise see a "supersedes"
+    # edge pointing at a claim id it was never told exists.
+    assert result["edges"] == []
 
 
 def test_find_neighbors_unknown_node_raises(store: KBStore) -> None: