fix(cron): do not misclassify empty/NO_REPLY as interim acknowledgement (#41401)

* fix(cron): do not misclassify empty/NO_REPLY as interim acknowledgement

When a cron task's agent returns NO_REPLY, the payload filter strips the
silent token, leaving an empty text string. isLikelyInterimCronMessage()
previously returned true for empty input, causing the cron runner to
inject a forced rerun prompt ('Your previous response was only an
acknowledgement...').

Change the empty-string branch to return false: empty text after payload
filtering means the agent deliberately chose silent completion, not that
it sent an interim 'on it' message.

Fixes #41246

* fix(cron): do not misclassify empty/NO_REPLY as interim acknowledgement

Fixes #41246. (#41383) thanks @jackal092927.

---------

Co-authored-by: xaeon2026 <xaeon2026@gmail.com>

src/cron/isolated-agent/subagent-followup.test.ts

@@ -47,8 +47,12 @@ describe("isLikelyInterimCronMessage", () => {
       false,
     );
   });
-  it("treats empty as interim", () => {
-    expect(isLikelyInterimCronMessage("")).toBe(true);
+  it("does not treat empty as interim (empty = NO_REPLY was stripped)", () => {
+    expect(isLikelyInterimCronMessage("")).toBe(false);
+  });
+
+  it("does not treat whitespace-only as interim", () => {
+    expect(isLikelyInterimCronMessage("   ")).toBe(false);
   });
 });
 

src/cron/isolated-agent/subagent-followup.ts

@@ -42,7 +42,10 @@ function normalizeHintText(value: string): string {
 export function isLikelyInterimCronMessage(value: string): boolean {
   const normalized = normalizeHintText(value);
   if (!normalized) {
-    return true;
+    // Empty text after payload filtering means the agent either returned
+    // NO_REPLY (deliberately silent) or produced no deliverable content.
+    // Do not treat this as an interim acknowledgement that needs a rerun.
+    return false;
   }
   const words = normalized.split(" ").filter(Boolean).length;
   return words <= 45 && INTERIM_CRON_HINTS.some((hint) => normalized.includes(hint));