reasoning: require structural progress for supported meaning

tests/graph/prompt-builder.test.js

@@ -129,3 +129,52 @@ describe("buildGraphUpdatePrompt", () => {
     );
   });
 });
+
+// ── Semantic-to-mutation contract (57J.39) ──────────────
+
+describe("buildGraphUpdatePrompt — semantic-to-mutation MUST rule", () => {
+  it("contains the explicit structural-materialization MUST rule", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    expect(prompt).toContain("MUST express its effect through structural mutation");
+  });
+
+  it("rule permits update/refine of existing structure", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    expect(prompt).toContain("update/refinement of existing structure");
+  });
+
+  it("rule permits resolving an existing unknown", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    expect(prompt).toContain("resolution of an existing unknown");
+  });
+
+  it("rule permits genuinely new unknown when needed", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    expect(prompt).toContain("a genuinely new unknown");
+  });
+
+  it("rule explicitly states answerMeaning alone is not sufficient", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    expect(prompt).toContain("answerMeaning alone is not sufficient");
+  });
+
+  it("rule does NOT force adding a new node", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    // The rule should be silent about forcing new nodes — this is preserved by existing rule #7.
+    // Verify the MUST rule exists but doesn't contain "must add a new node" or similar.
+    const mustRuleMatch = prompt.match(
+      /6\..*?(?=\n7\.)/s,
+    );
+    expect(mustRuleMatch).not.toBe(null);
+    expect(mustRuleMatch[0]).not.toContain("must add a new node");
+  });
+
+  it("does not imply possibleInference alone triggers mutation", () => {
+    const prompt = buildGraphUpdatePrompt(makeContext());
+    // The rule must reference userSupportedMeaning specifically, not possibleInference as a trigger.
+    const mustRuleMatch = prompt.match(
+      /6\..*?(?=\n7\.)/s,
+    );
+    expect(mustRuleMatch[0]).toContain("userSupportedMeaning");
+  });
+});