R-288: an empty cast declaration is fatal; a missing one still falls back

c0's point on R-286: the reader is unambiguous now, but the roster fallback that
made the failure look like success is still reachable. Narrowly closed -- sixteen
of the seventeen scenarios declare no cast and are rightly checked against the
whole roster, so only a marker that is PRESENT and names nobody is refused, with
its line named. Replacing the declaration with <!-- cast: --> passes before this
change and fails after it.

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

docs/REVIEW_LOG.md

@@ -6752,3 +6752,16 @@ sentences and there is no smaller slice that owns them, so it is left alone deli
 rather than overlooked. check-rules builds its covered-set from labels it generates, not from
 searching a document. check-lang, check-creatures, check-templates, check-kits and the
 baseline guards do no document matching at all.
+
+## R-288 — an empty declaration is not the same as no declaration
+
+c0's note on R-286: the reader is unambiguous now, but the fallback that made the failure
+look like success is still there. It is right, and the fix has to be narrow. **No marker at
+all is the ordinary case** — sixteen of the seventeen scenarios here declare no cast and are
+rightly checked against the whole duty roster. A marker that is present and names nobody is
+a different thing: somebody wrote a declaration, the guard read nothing out of it, and the
+fallback then widens the population silently, so a clue only Pollard can reach passes on the
+strength of an agent the scenario does not cast.
+
+Replacing CLEAN GROUND's declaration with `<!-- cast: -->` passes before this change and
+fails after it, naming the line. A scenario with no marker still falls back, unchanged.

tools/check-rollable.mjs

@@ -104,6 +104,19 @@ for (const [label, path] of scenarioFiles()) {
       + `skill in the document to it; the others were never seen. Keep one declaration and `
       + `put any example inside backticks, where the reader ignores it.`);
   }
+  /* A MARKER THAT DECLARES NOBODY MUST NOT FALL BACK. No marker at all is the ordinary case —
+     sixteen of the seventeen scenarios here have none and are rightly checked against the whole
+     duty roster. A marker that is PRESENT and EMPTY is a different thing: somebody wrote a
+     declaration and this guard read nothing out of it, and the fallback then widens the
+     population silently, so a clue only Pollard can reach passes on the strength of an agent
+     the scenario does not cast. That widening is what made R-286 green rather than loud; the
+     reader is unambiguous now, and this closes the door it came through. c0 asked for it. */
+  if (markers.length === 1 && !markers[0].keys.trim()) {
+    problems.push(`${label}: declares a cast at line ${markers[0].line} and names nobody in it. `
+      + `An empty declaration is not the same as no declaration — this guard would fall back to `
+      + `the full duty roster and check every skill in the document against people the scenario `
+      + `does not cast, and say OK. Name the cast or delete the marker.`);
+  }
   const declared = markers[0];
   const cast = declared
     ? declared.keys.split(",").map(x => x.trim()).filter(Boolean).map(k => {