reasoning: require structural progress for supported meaning

lib/graph/prompt-builder.js

@@ -92,7 +92,7 @@ The JSON object must contain exactly these top-level fields:
 3. Reference existing node IDs when updating an existing concept.
 4. Use addedNodes only for genuinely new concepts.
 5. Resolve the answered unknown first when the answer supports it.
-6. Then inspect the answer for newly introduced consequential uncertainty.
+6. If answerMeaning.userSupportedMeaning contains consequential information or unresolved uncertainty that is not already represented in the graph, you MUST express its effect through structural mutation. This may be an update/refinement of existing structure, resolution of an existing unknown, a genuinely new unknown, or a justified relationship. answerMeaning alone is not sufficient for a successful proposal.
 7. Add new unknown nodes only when the answer introduces a new decision, claim, object, measure, dependency, or unresolved term directly relevant to the case.
 8. Add at most 3 new unknown nodes.
 9. Every new unknown must be directly traceable to the user's answer and its description must state why that uncertainty matters.

lib/graph/utils.js

@@ -881,7 +881,15 @@ export function validateGraphUpdate(graph, update) {
     update.removedEdgeIds.length > 0;
 
   if (!hasMeaningfulChange) {
-    errors.push("Update contains no meaningful change");
+    // Specific diagnostic for the semantic-only no-op case: populated userSupportedMeaning with zero structural mutation.
+    // The validator does NOT determine whether meaning is "new" or "consequential" — it only observes that meaning exists without structural expression.
+    if (update.answerMeaning?.userSupportedMeaning) {
+      errors.push(
+        "answerMeaning.userSupportedMeaning is populated, but the proposal contains no graph mutation. answerMeaning alone does not constitute graph progress.",
+      );
+    } else {
+      errors.push("Update contains no meaningful change");
+    }
   }
 
   // Reject oversized input