diff --git a/src/auto-reply/reply/agent-runner.misc.runreplyagent.test.ts b/src/auto-reply/reply/agent-runner.misc.runreplyagent.test.ts
index 02fc22cf77d..2bfbd42c270 100644
--- a/src/auto-reply/reply/agent-runner.misc.runreplyagent.test.ts
+++ b/src/auto-reply/reply/agent-runner.misc.runreplyagent.test.ts
@@ -10,6 +10,7 @@ import { peekSystemEvents, resetSystemEventsForTest } from "../../infra/system-e
 import type { TemplateContext } from "../templating.js";
 import type { FollowupRun, QueueSettings } from "./queue.js";
 import { createMockTypingController } from "./test-helpers.js";
+import { BILLING_ERROR_USER_MESSAGE } from "../../agents/pi-embedded-helpers.js";
 
 const runEmbeddedPiAgentMock = vi.fn();
 const runCliAgentMock = vi.fn();
@@ -224,6 +225,20 @@ describe("runReplyAgent onAgentRunStart", () => {
     });
   });
 
+  it("returns billing message for mixed-signal error", async () => {
+    runEmbeddedPiAgentMock.mockRejectedValueOnce(
+      new Error(
+        "HTTP 402 Payment Required: insufficient credits. Request size exceeds model context window.",
+      ),
+    );
+
+    const result = await createRun();
+    const payload = Array.isArray(result) ? result[0] : result;
+
+    expect(payload?.text).toBe(BILLING_ERROR_USER_MESSAGE);
+    expect(payload?.text).not.toContain("Context overflow");
+  });
+
   it("emits start callback when cli runner starts", async () => {
     runCliAgentMock.mockResolvedValueOnce({
       payloads: [{ text: "ok" }],