test(rectification): lock failReceipt engine_message for compare failures

BUG-659 moved compare tool_failed fingerprints into failReceipt; keep the
source lock on the shared helper so the staging gate still requires a
redacted engine_message.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/tests/rectification-stale-compare-fix-20260907.test.ts

@@ -223,7 +223,12 @@ test("compare failure copy and receipt detail stay user-visible without PII", ()
   assert.match(agentRun, /withCompareFailedRetryNotice/);
   assert.match(agentRun, /rectification-compare-candidates/);
   const tools = readFileSync(new URL("../src/mastra/rectification-v9-tools.ts", import.meta.url), "utf8");
-  assert.match(tools, /engine_message: engineMessageForReceipt/);
+  // 原值: /engine_message: engineMessageForReceipt/ 写在 compare catch 里
+  // 新值: failReceipt 统一写 engine_message，compare catch 调用它
+  // 原因: BUG-659 失败回执抽成共享 helper，源码锁仍要保住脱敏原文
+  assert.match(tools, /const message = engineMessageForReceipt\(error\)/);
+  assert.match(tools, /engine_message: message/);
+  assert.match(tools, /failReceipt\("rectification-compare-candidates"/);
 });
 
 test("idle persist on a stale snapshot calls candidate score once", async () => {