feat(consume): a question that accounts for a concept's WHOLE title takes it first

`title_covered_hits` names the concepts whose every title token is a token of
the question, and `concept_scores` reads them before the rest -- a PARTITION
below the lookup partition, never a fourth RRF signal.

The arithmetic that rules a signal out is the same one `lookup_hits` was made
a partition on: RRF consumes ranks alone, so with shared ranks a rule whose
positive group is SMALL separates least of all. Measured on a 2 761-concept
bundle of one standard, the group is 1, 1, 1, 1, 9, 2, 0 and 0 concepts over
the eight questions -- as a signal it moved hit@1 not at all.

By EQUALITY and never by shared prefix: four shared leading characters take
the group from 1 to 6 on one question and 9 to 31 on another, and the
answering section falls to candidate rank 6 with the known-positive to 2.

ON by default with the opt-out `--no-title-covered`. Suite: 1580 passed,
1 skipped; the pinned K2 bundle green and unchanged.

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

src/llm_ingestion_okf/consume.py

@@ -1158,6 +1158,77 @@ DEFAULT_TIE_SHARED_RANK = True
 DEFAULT_STEM_PREFIX = True
 
 
+#: Round 16. Whether a concept whose WHOLE title the question accounts for is
+#: read before the concepts the fusion ranked above it. ON since 2026-09-11.
+#:
+#: THE DEFECT IT REPAIRS. Both lexical signals are unnormalised COVERAGE
+#: COUNTS -- one per question token the candidate answers to -- so nothing in
+#: the fusion measures how much of the CANDIDATE the question accounts for. A
+#: section titled with the question's subject and nothing else scores exactly
+#: what a narrower section titled with that subject PLUS a qualifier scores,
+#: and then loses to it on the body count. Measured 2026-09-11 on a
+#: 2 761-concept bundle of one standard, where the answering section carries
+#: the bare term as its title on three of six scored questions: `Hovedprosesser`
+#: behind `Hovedprosess 81 ...`, `Armering` behind `Armering av ...`,
+#: `Inspeksjon` behind `Enkel inspeksjon`.
+#:
+#: WHY A PARTITION AND NOT A FOURTH SIGNAL, measured rather than argued. RRF
+#: consumes RANKS ONLY, and with shared ranks a signal whose positive group is
+#: SMALL separates least of all: the group takes position 1 and everyone else
+#: position `len(group) + 1`, so a rule firing on 1 concept of 2 761 is worth
+#: `1/61 - 1/62` to it -- an order of magnitude under the body-signal gap it
+#: has to close. Measured as a signal on that bundle it moved hit@1 not at all
+#: (3 of 6); as a partition it reaches 6 of 6 candidate rank 1 with the
+#: known-positive still at rank 1. `lookup_hits` is the same shape and was made
+#: a partition on the same arithmetic.
+#:
+#: LIKE `--tie-shared-rank` AND `--stem-prefix`, THIS MOVES A PAYLOAD WITH NO
+#: BUNDLE CHANGING. A consumer pinned to the previous excerpt order needs
+#: `--no-title-covered`.
+DEFAULT_TITLE_COVERED = True
+
+
+def title_covered_hits(concepts: Sequence["Concept"], question: str) -> tuple[str, ...]:
+    """The concepts whose ENTIRE title the question accounts for.
+
+    Every token of the title is a token of the question, so the title says
+    nothing the question did not ask about. That is a statement about the
+    CANDIDATE -- the complement of the coverage counts, which are statements
+    about the question -- and it is the one thing separating a section titled
+    with the subject from a narrower section titled with the subject plus a
+    qualifier.
+
+    **BY EQUALITY, never by shared prefix, and that is measured rather than
+    assumed.** `tokens_match` accepts four shared leading characters, which
+    would admit `Anchorage` beside `Anchoring` and, on the 2 761-concept
+    bundle, took the group from 1 concept to 6 on one question and from 9 to 31
+    on another -- the answering section falling to candidate rank 6 and the
+    known-positive to rank 2. Under equality both hold rank 1. The precedent is
+    `tokens_match`'s own: an identifier matches by equality alone, for the same
+    reason -- a prefix rule built for compounds says nothing true about a name.
+
+    Returns the EMPTY tuple when no concept qualifies, which is what makes the
+    rule invisible to every question that names no section outright. Byte
+    sorted, so several holders of one title arrive in a declared order.
+
+    Reads `title` alone and not the concept id: an id segment is this
+    library's reduction of a title, so counting it would let the same words
+    qualify a concept twice, and the document uuid that the id carries on a
+    single-document bundle is in no question ever asked.
+    """
+    question_tokens = set(normalise(question))
+    if not question_tokens:
+        return ()
+    return tuple(
+        sorted(
+            concept.concept_id
+            for concept in concepts
+            if (title_tokens := normalise(concept.title))
+            and all(token in question_tokens for token in title_tokens)
+        )
+    )
+
+
 def concept_scores(
     concepts: Sequence[Concept],
     question: str,
@@ -1167,6 +1238,7 @@ def concept_scores(
     weights: Mapping[str, float] | None = None,
     lookup: bool = True,
     tie_shared_rank: bool = DEFAULT_TIE_SHARED_RANK,
+    title_covered: bool = DEFAULT_TITLE_COVERED,
     stems: frozenset[str] | None = None,
 ) -> list[tuple[Concept, float, int]]:
     """Every concept, ordered best first, fused from three signals by RRF.
@@ -1301,6 +1373,18 @@ def concept_scores(
     )
     by_id = {concept.concept_id: concept for concept in concepts}
     ranked_ids = sorted(fused, key=lambda key: (-fused[key], key))
+    covered = set(title_covered_hits(concepts, question)) if title_covered else set()
+    if covered:
+        # A PARTITION, not a signal, and it lands BELOW the lookup partition
+        # so a question that NAMES a concept still reads that one first. See
+        # `DEFAULT_TITLE_COVERED` for the arithmetic that rules a signal out,
+        # and `tests/test_title_covered.py` for the mechanism on a fixture.
+        #
+        # STABLE: both parts keep the order the fusion gave them, so nothing
+        # here depends on dict order.
+        ranked_ids = [key for key in ranked_ids if key in covered] + [
+            key for key in ranked_ids if key not in covered
+        ]
     named = set(lookup_hits(concepts, question)) if lookup else set()
     if named:
         # THE LOOKUP LANDS BEFORE THE FUSION'S OUTPUT IS READ, and it is a
@@ -1627,6 +1711,7 @@ def build_payload(
     reserve_top_rank: bool = False,
     rarity_weight: bool = False,
     tie_shared_rank: bool = DEFAULT_TIE_SHARED_RANK,
+    title_covered: bool = DEFAULT_TITLE_COVERED,
     withheld_titles: bool = False,
     stem_prefix: bool = DEFAULT_STEM_PREFIX,
     source_quota: int | None = DEFAULT_SOURCE_QUOTA,
@@ -1635,7 +1720,8 @@ def build_payload(
 
     Pure with respect to the clock and the network: the same
     `(bundle_root, question, k, limit, cost_vocabulary, reserve_top_rank,
-    rarity_weight, tie_shared_rank, withheld_titles)` at the same bytes returns
+    rarity_weight, tie_shared_rank, title_covered, withheld_titles)` at the
+    same bytes returns
     the same object, every time.
 
     **`withheld_titles` (default off) names what was dropped.** A `withheld`
@@ -1703,6 +1789,7 @@ def build_payload(
         cost_vocabulary=cost_vocabulary,
         weights=weights,
         tie_shared_rank=tie_shared_rank,
+        title_covered=title_covered,
         stems=stems,
     )
     titles_by_id = {concept.concept_id: concept.title for concept in concepts}
@@ -1883,6 +1970,26 @@ def parse_args(argv: list[str] | None) -> argparse.Namespace:
         dest="stem_prefix",
         help="The rule's explicit opt-out, reproducing the pre-round-10 matcher",
     )
+    parser.add_argument(
+        "--title-covered",
+        action="store_true",
+        default=DEFAULT_TITLE_COVERED,
+        help=(
+            "read a concept whose WHOLE title the question accounts for before "
+            "the concepts the fusion ranked above it. ON since 2026-09-11. "
+            "Measured on a 2 761-concept bundle of one standard: hit@1 over six "
+            "questions 3 of 6 -> 6 of 6 with the known-positive holding rank 1, "
+            "where none of the six existing reading-side flags moved that "
+            "number at all. The title is read by EQUALITY, never by shared "
+            "prefix. See docs/2026-09-11-k3-runde16-hele-tittelen-tar-ruten.md"
+        ),
+    )
+    parser.add_argument(
+        "--no-title-covered",
+        action="store_false",
+        dest="title_covered",
+        help="The rule's explicit opt-out, reproducing the pre-round-16 excerpt order",
+    )
     parser.add_argument(
         "--source-quota",
         type=int,
@@ -1951,6 +2058,7 @@ def main(argv: list[str] | None = None) -> int:
             reserve_top_rank=args.reserve_top_rank,
             rarity_weight=args.rarity_weight,
             tie_shared_rank=args.tie_shared_rank,
+            title_covered=args.title_covered,
             stem_prefix=args.stem_prefix,
             source_quota=args.source_quota,
             withheld_titles=args.withheld_titles,