fix(graph): make structural action contract authoritative

lib/graph/utils.js

@@ -900,24 +900,28 @@ export function validateGraphUpdate(graph, update) {
     errors.push("structuralActionRequired is false but proposal contains meaningful mutations");
   }
 
-  // Legacy no-op guard: only fires when structuralActionRequired !== false.
-  // When false → zero-mutation is a valid intentional no-op (contract PASS).
-  if (!hasMeaningfulChange && update.structuralActionRequired !== false) {
+  // Legacy no-op guard: only fires when structuralActionRequired is absent (null/undefined).
+  // When true or false → the new contract owns no-op/mutation consistency.
+  // The contract checks above already produced authoritative errors for those cases.
+
+  const fieldAbsent =
+    update.structuralActionRequired === null ||
+    update.structuralActionRequired === undefined;
+
+  if (!hasMeaningfulChange && fieldAbsent) {
     if (meaningPopulated) {
-      // Avoid double-error when field absence was already flagged above
-      if (
-        update.structuralActionRequired !== null &&
-        update.structuralActionRequired !== undefined
-      ) {
-        errors.push(
-          "answerMeaning.userSupportedMeaning is populated, but the proposal contains no graph mutation. answerMeaning alone does not constitute graph progress.",
-        );
-      }
+      // structuralActionRequired was missing while userSupportedMeaning exists.
+      // Missing-field rejection already added above; skip semantic-only guard to avoid duplicate errors on the same proposal.
     } else if (!meaningPopulated) {
       errors.push("Update contains no meaningful change");
     }
   }
 
+  // Legacy guard when structuralActionRequired=false: false declares no action needed,
+  // but userSupportedMeaning populated implies semantic intent for change. However the
+  // new-contract checks above already produced an error if there IS mutation. If there's
+  // zero mutation with false + meaning, treat as intentional no-op (contract PASS).
+
   // Reject oversized input
   const totalSize = JSON.stringify(update).length;
   if (totalSize > 100000) {