test(consume): a drop the rank had already made must not be named as the quota's

Red first, on behaviour: the withheld set names c4 and c5 as
`source_quota_exceeded` where the same cut without the quota withholds them
`below_k`. The test measures the truth itself, off a second cut, and
carries a known-positive so the assertion is not vacuous.

Measured by PM on 25 real misses 2026-09-17: 13 were labelled by the quota
and decided by the rank.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_okf_consume.py

@@ -2609,3 +2609,40 @@ def test_a_source_key_is_a_prefix_and_never_a_substring(tmp_path: Path) -> None:
     )
     assert excerpt is not None
     assert "resource_owner" not in excerpt
+
+
+def test_a_drop_the_rank_had_already_made_is_not_named_as_the_quotas() -> None:
+    """The reason a withheld concept carries must be true OF THAT DROP.
+
+    The quota filters the WHOLE candidate list, not the top k, so every
+    over-quota candidate came back `source_quota_exceeded` -- including the
+    ones the rank had already put outside k, which the quota only reached
+    because it ran first. Measured by PM on 25 real misses 2026-09-17: 13 of
+    them were labelled by the quota and decided by the rank.
+
+    The truth is the SAME cut run without the quota, which is what the
+    retrieval gate's row 3 compares the label against.
+    """
+    concepts = tuple(
+        _quota_concept(f"c{index}", source_file="o.md" if index < 6 else f"x{index}.md")
+        for index in range(10)
+    )
+    ranked = tuple((concept, 1.0 / (index + 1), 3) for index, concept in enumerate(concepts))
+    _, withheld, _ = okf_consume.cut(ranked, k=4, limit=okf_consume.DEFAULT_LIMIT, source_quota=2)
+    rules = dict(withheld)
+    # The truth, measured here rather than taken from the cut under test.
+    off_delivered, _, _ = okf_consume.cut(
+        ranked, k=4, limit=okf_consume.DEFAULT_LIMIT, source_quota=None
+    )
+    would_have_been_delivered = {str(entry["concept_id"]) for entry in off_delivered}
+    assert would_have_been_delivered == {"c0", "c1", "c2", "c3"}
+
+    named_by_the_quota = {cid for cid, rule in withheld if rule == "source_quota_exceeded"}
+    # KNOWN-POSITIVE: the quota really does decide something on this fixture,
+    # so the assertion below is not vacuous over an empty set.
+    assert named_by_the_quota, "the quota decided nothing here; the test measures nothing"
+    assert named_by_the_quota == {"c2", "c3"}
+    assert named_by_the_quota <= would_have_been_delivered
+    # And the two the rank had already lost say so.
+    assert rules["c4"] == "below_k"
+    assert rules["c5"] == "below_k"