diff --git a/tests/test_integration_rule_surfacing.py b/tests/test_integration_rule_surfacing.py
index cf1302e..1825954 100644
--- a/tests/test_integration_rule_surfacing.py
+++ b/tests/test_integration_rule_surfacing.py
@@ -118,6 +118,19 @@ async def test_co_surfaces_drags_in_the_half_that_would_have_been_missed(world):
         "A name decides nothing.",
         when_to_apply="when naming a build",
     )
+    # TAGGED TO AN AREA THIS PROJECT DOES NOT WORK IN, which is what makes the
+    # test able to fail at all. Since milestone 394 an UNTAGGED rule in a
+    # subscribed rulebook applies on its own, so an untagged partner arrives
+    # through the ordinary query and the edge is never exercised — the
+    # assertion below passed while proving nothing, which is how this was
+    # noticed. Tagging it puts it out of reach of everything except the edge.
+    area = await canonical_svc.find_by_name("CI & Release")
+    assert area is not None, "migration 0087 seeds the standard vocabulary"
+    await rulebooks_svc.set_rule_systems(partner.id, world["owner"], [area.id])
+    assert "Version names are labels" not in await _titles(world), (
+        "the partner must be unreachable on its own, or this test cannot fail"
+    )
+
     await rulebooks_svc.add_rule_relation(
         world["owner"], world["plain"], partner.id, "co_surfaces",
         note="they fail together",
@@ -132,6 +145,9 @@ async def test_co_surfaces_drags_in_the_half_that_would_have_been_missed(world):
 async def test_a_suppression_outranks_an_edge(world):
     """The edge says these belong together; the suppression says this project
     does not want that one. An explicit decision beats an inferred one."""
+    # Untagged on purpose, unlike the partner above: this test is about the
+    # SUPPRESSION winning, so the partner should be one that would otherwise
+    # arrive by every available route — the ordinary query AND the edge.
     partner = await rulebooks_svc.create_rule(
         world["topic"], world["owner"], "Muted partner", "Should not arrive.",
     )