diff --git a/src/cron/isolated-agent/helpers.test.ts b/src/cron/isolated-agent/helpers.test.ts
index 31e533170..365125764 100644
--- a/src/cron/isolated-agent/helpers.test.ts
+++ b/src/cron/isolated-agent/helpers.test.ts
@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import {
+  isHeartbeatOnlyResponse,
   pickLastDeliverablePayload,
   pickLastNonEmptyTextFromPayloads,
   pickSummaryFromPayloads,
@@ -84,3 +85,65 @@ describe("pickLastDeliverablePayload", () => {
     expect(pickLastDeliverablePayload([normal, error])).toBe(normal);
   });
 });
+
+describe("isHeartbeatOnlyResponse", () => {
+  const ACK_MAX = 300;
+
+  it("returns true for empty payloads", () => {
+    expect(isHeartbeatOnlyResponse([], ACK_MAX)).toBe(true);
+  });
+
+  it("returns true for a single HEARTBEAT_OK payload", () => {
+    expect(isHeartbeatOnlyResponse([{ text: "HEARTBEAT_OK" }], ACK_MAX)).toBe(true);
+  });
+
+  it("returns false for a single non-heartbeat payload", () => {
+    expect(isHeartbeatOnlyResponse([{ text: "Something important happened" }], ACK_MAX)).toBe(
+      false,
+    );
+  });
+
+  it("returns true when multiple payloads include narration followed by HEARTBEAT_OK", () => {
+    // Agent narrates its work then signals nothing needs attention.
+    expect(
+      isHeartbeatOnlyResponse(
+        [
+          { text: "It's 12:49 AM — quiet hours. Let me run the checks quickly." },
+          { text: "Emails: Just 2 calendar invites. Not urgent." },
+          { text: "HEARTBEAT_OK" },
+        ],
+        ACK_MAX,
+      ),
+    ).toBe(true);
+  });
+
+  it("returns false when media is present even with HEARTBEAT_OK text", () => {
+    expect(
+      isHeartbeatOnlyResponse(
+        [{ text: "HEARTBEAT_OK", mediaUrl: "https://example.com/img.png" }],
+        ACK_MAX,
+      ),
+    ).toBe(false);
+  });
+
+  it("returns false when media is in a different payload than HEARTBEAT_OK", () => {
+    expect(
+      isHeartbeatOnlyResponse(
+        [
+          { text: "HEARTBEAT_OK" },
+          { text: "Here's an image", mediaUrl: "https://example.com/img.png" },
+        ],
+        ACK_MAX,
+      ),
+    ).toBe(false);
+  });
+
+  it("returns false when no payload contains HEARTBEAT_OK", () => {
+    expect(
+      isHeartbeatOnlyResponse(
+        [{ text: "Checked emails — found 3 urgent messages from your manager." }],
+        ACK_MAX,
+      ),
+    ).toBe(false);
+  });
+});
diff --git a/src/cron/isolated-agent/helpers.ts b/src/cron/isolated-agent/helpers.ts
index c74b65d1b..5e7f92990 100644
--- a/src/cron/isolated-agent/helpers.ts
+++ b/src/cron/isolated-agent/helpers.ts
@@ -94,13 +94,18 @@ export function isHeartbeatOnlyResponse(payloads: DeliveryPayload[], ackMaxChars
   if (payloads.length === 0) {
     return true;
   }
-  return payloads.every((payload) => {
-    // If there's media, we should deliver regardless of text content.
-    const hasMedia = (payload.mediaUrls?.length ?? 0) > 0 || Boolean(payload.mediaUrl);
-    if (hasMedia) {
-      return false;
-    }
-    // Use heartbeat mode to check if text is just HEARTBEAT_OK or short ack.
+  // If any payload has media, deliver regardless — there's real content.
+  const hasAnyMedia = payloads.some(
+    (payload) => (payload.mediaUrls?.length ?? 0) > 0 || Boolean(payload.mediaUrl),
+  );
+  if (hasAnyMedia) {
+    return false;
+  }
+  // An agent may emit multiple text payloads (narration, tool summaries)
+  // before a final HEARTBEAT_OK. If *any* payload is a heartbeat ack token,
+  // the agent is signaling "nothing needs attention" — the preceding text
+  // payloads are just internal narration and should not be delivered.
+  return payloads.some((payload) => {
     const result = stripHeartbeatToken(payload.text, {
       mode: "heartbeat",
       maxAckChars: ackMaxChars,