test: the empty duplicate report carries suggestion now — assert shape, not the exact dict

The step-5 field addition (d7039dc) broke a test pinning the error-path
return literally. The field is deliberate: a failed scan must match a clean
scan in shape, or every consumer grows a second code path for the degraded
case. Assert the parts instead.

Refs #2547

tests/test_snippet_duplicates.py

@@ -96,4 +96,9 @@ async def test_a_failed_scan_returns_an_empty_report_not_an_error():
         patch.object(dedup_svc, "async_session", side_effect=RuntimeError("boom")),
     ):
         out = await dedup_svc.find_duplicate_snippets(1)
-    assert out == {"groups": [], "pairs": [], "threshold": 0.8}
+    # The empty report still carries its per-kind `suggestion` (#2547) — a
+    # failed scan must be indistinguishable in SHAPE from a clean one, or every
+    # consumer needs a second code path for the degraded case.
+    assert out["groups"] == [] and out["pairs"] == []
+    assert out["threshold"] == 0.8
+    assert "merge" in out["suggestion"]