feat(consume): the payload says when the bundle looks like it does not cover the question

C4. `coverage` gains two keys, and every key it had keeps its bytes:

- `absent_terms`: the question's words the bundle holds in NO form -- not as
  written, and not through a relative it uses (`bm25.query_groups`, the same
  bridge the ranking reads through);
- `weak`: true when one such word exists or nothing was delivered.

A reading with its rule in the open, never a verdict about the bundle. It is
computed for both rankings (`bm25.absent_terms` serves the fusion). The
retrieval gate's `marked` -- the one reading both gates share -- reads `weak`
beside its own bar, never instead of it; the known-negative that strips the
payload's words now strips both readings.

Words that only FRAME a question are stopwords in both languages (`how
often`, `hvor ofte`, `hva står i`, `what does it say`), and so are the
Norwegian function words spelled without their letters (`naar`, `paa`), the way
ASCII-only text writes them. Read as topic words they would be "absent" from
any collection that never uses them, which is what the synthetic sets showed
on three answered questions before the list was extended.

The working method says what to do with it, in one sentence each: the skill
template's step 3 and the MCP server's instructions (1 253 bytes, under the
2 048 a client keeps) -- rephrase in the bundle's words, and if it stays weak,
say the bundle does not cover the question.

The search gate's table for this commit is kept in local state.

Suite on a clean tree after `git add`: 2397 passed, 2 skipped, 4 xfailed.
ruff, ruff format, mypy --strict clean. Retrieval gate unchanged at the rows
the previous commit left red.

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

tests/test_bm25_ranking.py

@@ -189,3 +189,17 @@ def test_a_concept_named_by_its_number_carries_a_lexical_match() -> None:
     ranked = bm25.rank(concepts, "Hva staar i punkt 4.2 om kontrollen av hytta?").ranked
     lexical = {concept.concept_id: count for concept, _, count in ranked}
     assert lexical["r/vakthold-4-2"] >= 1
+
+
+def test_a_norwegian_function_word_written_without_its_letters_is_a_stopword() -> None:
+    # ASCII-only text writes `når` as `naar`; it is the same function word and
+    # must not read as a content word the collection lacks.
+    assert bm25.tokens("Naar skjer det paa hytta?") == bm25.tokens("Når skjer det på hytta?")
+
+
+def test_a_word_that_frames_a_question_is_not_a_topic() -> None:
+    # `how often` / `hvor ofte` asks about a topic without naming one; read as
+    # a topic word it would be "absent" from any collection that never says it.
+    assert bm25.tokens("How often is the battery replaced?") == ["battery", "replac"]
+    assert bm25.tokens("Hvor ofte byttes batteriet?") == ["bytt", "batteriet"]
+    assert bm25.tokens("Hva står i punkt 4.2?") == bm25.tokens("punkt 4.2")