fix(retrieval-gate): row 5 reads the hold-out set in the schema the set declares

Row 5 read every registered set with the gate's synthetic reader, so a
set written in a consumer's own question-set schema came back "not a
question set this gate can read: 'set_id'" -- a NO no such set could
turn, whatever it measured.

The SET now says how it is read, and the registration carries nothing
about it: `read_hold_out_set` checks the pinned sha256, then routes on
the set's own `schema` field. `fase-sporsmaal/1` goes through the same
adapter and hit_rule as row 8 (`_wiki_questions`, factored out of
`read_real_set` so the two rows share one reading); a set with no
`schema` is the gate's synthetic form through `load_set`, unchanged;
any other schema is a NO that names it (fail closed).

Chosen to recognise the set's schema rather than add a field to the
registration because the registration then needs to know nothing about
the reading, and an unknown schema still fails with a named reason.

The row still prints only answered of asked against the threshold, never
which hold-out question missed; a test holds that. src/ untouched,
MUTANT_BAR unchanged. CLAUDE.md gains one sentence on row 5.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -1385,7 +1385,13 @@ and fixtures, never code.
   itself; three now read GIT (committed and unmodified, its commit is not
   itself a ranking change, a ranking change landed AFTER it), the last being
   the one that cannot be self-attested. What git cannot prove -- that nobody
-  read the number first -- is stated, not implied. **Row 7's bar** was 90 % of
+  read the number first -- is stated, not implied. Since 2026-09-23 row 5
+  reads the hold-out set in the schema the SET declares
+  (`HOLD_OUT_SCHEMAS`: `fase-sporsmaal/1` goes through row 8's own adapter
+  and `hit_rule`, no `schema` is the gate's synthetic form, any other schema
+  is a NO naming it) -- it read every set with the synthetic reader, so a set
+  in a consumer's schema was a NO nothing could turn. It prints the share and
+  never which hold-out question missed, and a test holds that. **Row 7's bar** was 90 % of
   a list in the file a capability session edits, so seven duplicate `k = 1`
   mutants read `18 of 20 GREEN`; `MUTANT_ROSTER` and `MUTANT_COUNT` are pinned
   apart from `MUTANTS`, duplicates are refused, and the bar is the roster's.

tools/okf_retrieval_gate.py

@@ -75,8 +75,8 @@ from llm_ingestion_okf.quality import (  # noqa: E402
 
 FIXTURES = REPO / "tests" / "fixtures" / "retrieval"
 
-#: The hold-out registration. Absent today, which is what makes row 5 red; the
-#: row reads a path so a test can drive both directions without editing code.
+#: The hold-out registration. The row reads a path so a test can drive both
+#: directions without editing code.
 HOLDOUT_REGISTRATION = FIXTURES / "holdout-registration.json"
 
 GREEN = "GREEN"
@@ -1662,7 +1662,7 @@ def _hold_out_verdict(
     if not set_path.is_file():
         return False, f"the set is absent at {_display(set_path)}"
     try:
-        question_set = load_set(set_path, pinned)
+        question_set = read_hold_out_set(set_path, pinned)
         bundles = _bundle_map(bundle)
         if list(bundles) == [""] and question_set.bundle:
             bundles = {question_set.bundle: bundles[""]}
@@ -2212,23 +2212,72 @@ def read_real_set(name: str, path: Path, expected_sha256: str) -> QuestionSet:
         )
     spec = json.loads(raw.decode("utf-8"))
     if name == "wiki":
-        # The set's own `hit_rule`, verbatim: an excerpt whose `source_file` is
-        # the fasit's document AND whose text carries the fasit's quote.
-        questions = tuple(
-            Question(
-                id=str(entry["id"]),
-                question=str(entry["question"]),
-                fasit=tuple(
-                    Fasit(by="source_file", value=f"{item['doc']}.md", quote=str(item["quote"]))
-                    for item in entry["fasit"]
-                ),
-            )
-            for entry in spec["questions"]
-        )
-        return QuestionSet("wiki-20", "wiki", path, measured, questions, ())
+        return QuestionSet("wiki-20", "wiki", path, measured, _wiki_questions(spec), ())
     raise GateUsage(f"unknown real set `{name}`; the one real set is `wiki`")
 
 
+def _wiki_questions(spec: Mapping[str, Any]) -> tuple[Question, ...]:
+    """The wiki set's own `hit_rule`, verbatim: an excerpt whose `source_file`
+    is the fasit's document AND whose text carries the fasit's quote. One
+    reading of the schema, shared by row 8 and row 5."""
+    return tuple(
+        Question(
+            id=str(entry["id"]),
+            question=str(entry["question"]),
+            fasit=tuple(
+                Fasit(by="source_file", value=f"{item['doc']}.md", quote=str(item["quote"]))
+                for item in entry["fasit"]
+            ),
+        )
+        for entry in spec["questions"]
+    )
+
+
+#: The schemas a registered hold-out set may declare in its own `schema`
+#: field, and the bundle key its questions are read under. The SET says how
+#: it is read, so the registration carries nothing about it; a set with no
+#: `schema` is in this gate's own synthetic form (`load_set`), and a schema
+#: not named here is a NO with its name -- a set read in a shape it was not
+#: written in measures nothing.
+HOLD_OUT_SCHEMAS: Mapping[str, str] = {"fase-sporsmaal/1": "wiki"}
+
+
+def read_hold_out_set(path: Path, expected_sha256: str) -> QuestionSet:
+    """The registered hold-out set, read in the schema it declares.
+
+    Raises GateUsage for a set that is not the pinned bytes or declares a
+    schema this gate does not read; `_hold_out_verdict` turns either into a
+    NO with its reason.
+    """
+    try:
+        raw = path.read_bytes()
+    except OSError as error:
+        raise GateUsage(f"cannot read the question set {path}: {error}") from error
+    measured = hashlib.sha256(raw).hexdigest()
+    if measured != expected_sha256:
+        raise GateUsage(
+            f"{path}: expected sha256 {expected_sha256}, measured {measured}; "
+            "refusing to measure a set that is not the set that was pinned"
+        )
+    try:
+        spec = json.loads(raw.decode("utf-8"))
+    except (UnicodeDecodeError, json.JSONDecodeError) as error:
+        raise GateUsage(f"{path}: not readable as JSON: {error}") from error
+    schema = spec.get("schema") if isinstance(spec, dict) else None
+    if schema is None:
+        return load_set(path, expected_sha256)
+    if schema not in HOLD_OUT_SCHEMAS:
+        raise GateUsage(
+            f"the set's schema `{schema}` is not one this gate reads "
+            f"({', '.join(HOLD_OUT_SCHEMAS)}, or no `schema` for this gate's own form)"
+        )
+    try:
+        questions = _wiki_questions(spec)
+    except (KeyError, TypeError, ValueError) as error:
+        raise GateUsage(f"{path}: not a `{schema}` set this gate can read: {error}") from error
+    return QuestionSet("hold-out", HOLD_OUT_SCHEMAS[schema], path, measured, questions, ())
+
+
 #: The sets row 8 is the measurement of, by name: a run that hands over some
 #: of them has measured some of them, and the row says so. Left to
 #: `len(real)` the row came back `6 of 6 GREEN` on one set of three (PM's J2,