diff --git a/services/api/tests/test_resolve_determinism.py b/services/api/tests/test_resolve_determinism.py
index a3f2a14..0a522f9 100644
--- a/services/api/tests/test_resolve_determinism.py
+++ b/services/api/tests/test_resolve_determinism.py
@@ -2,8 +2,9 @@
 
 The removed Python scorer is deliberately not tested because it no longer
 exists. These tests pin the load-bearing adapter semantics instead:
-canonical match edges merge; review/non-match edges do not; merge application
-is deterministic; bridge failure leaves records unmerged.
+canonical match edges merge; review/non-match edges do not; hard negative
+identity evidence constrains the whole cluster; bridge failure leaves records
+unmerged.
 """
 from __future__ import annotations
 
@@ -38,22 +39,19 @@ def _rec(name: str, source: str, confidence: float = 0.9) -> dict:
     }
 
 
-def _pair(a: str, b: str, status: str = "match") -> dict:
+def _pair(a: str, b: str, status: str = "match", decided_by: str = "score", score: float = 0.97) -> dict:
     return {
         "candidate_id": f"c_{a}_{b}",
         "record_a": a,
         "record_b": b,
-        "score": 0.97,
+        "score": score,
         "status": status,
-        "decided_by": "score",
+        "decided_by": decided_by,
     }
 
 
 def test_apply_matches_is_deterministic_and_uses_canonical_edges_only():
     records = [_rec("Acme AB", "source-a", 0.91), _rec("ACME Aktiebolag", "source-b", 0.96)]
-    # The helper's ids are private implementation detail. Capture them by
-    # asking the live adapter body in the async test below; here we verify the
-    # no-edge contract and review-band safety directly.
     assert len(_apply_matches(copy.deepcopy(records), [])) == 2
 
 
@@ -106,6 +104,40 @@ async def test_pending_review_never_auto_merges(monkeypatch):
     assert all(not r.get("merged_from") for r in result)
 
 
+@pytest.mark.asyncio
+@respx.mock
+async def test_hard_non_match_blocks_transitive_cluster_merge(monkeypatch):
+    """A-B and B-C matches may never imply A=C when canonical hard evidence says A!=C."""
+    monkeypatch.setenv("OPT_ER_BRIDGE_URL", "https://edge.example.test")
+    monkeypatch.setenv("INTERNAL_TOKEN", "test-internal-token")
+    records = [
+        _rec("Acme AB", "source-a", 0.95),
+        _rec("Acme AB", "source-b", 0.94),
+        _rec("Acme AB", "source-c", 0.93),
+    ]
+
+    def responder(request: httpx.Request) -> httpx.Response:
+        body = __import__("json").loads(request.content)
+        a, b, c = [item["record_id"] for item in body["records"]]
+        return httpx.Response(
+            200,
+            json={
+                "pairs": [
+                    _pair(a, b, "match", "score", 0.98),
+                    _pair(b, c, "match", "score", 0.97),
+                    _pair(a, c, "non_match", "0pt.company.stable-identifiers.v2", 0.0),
+                ],
+                "review_queue": [],
+            },
+        )
+
+    respx.post("https://edge.example.test/api/0pt/internal/er/candidates").side_effect = responder
+    result = await resolve(records, tenant_id="tenant-a", project_id="project-a")
+    assert len(result) == 2
+    assert max(r.get("agreed_sources", 1) for r in result) == 2
+    assert not any(set(r.get("merged_from", [])) >= {"source-b", "source-c"} for r in result)
+
+
 @pytest.mark.asyncio
 @respx.mock
 async def test_bridge_outage_fails_closed_to_unmerged_records(monkeypatch):