diff --git a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
index 5c40bf58369..bb5aa36dba2 100644
--- a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
+++ b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
@@ -535,6 +535,8 @@ describe("classifyFailoverReason", () => {
     ).toBe("rate_limit");
     expect(classifyFailoverReason("all credentials for model x are cooling down")).toBeNull();
     expect(classifyFailoverReason("invalid request format")).toBe("format");
+    expect(classifyFailoverReason("credit balance too low")).toBe("billing");
+    // Billing with "limit exhausted" must stay billing, not rate_limit (avoids key-disable regression)
     expect(
       classifyFailoverReason("HTTP 402 payment required. Your limit exhausted for this plan."),
     ).toBe("billing");
@@ -593,6 +595,7 @@ describe("classifyFailoverReason", () => {
         "LLM error 1310: Weekly/Monthly Limit Exhausted. Your limit will reset at 2026-03-06 22:19:54 (request_id: 20260303141547610b7f574d1b44cb)",
       ),
     ).toBe("rate_limit");
+    // Independent coverage for /weekly\/monthly limit/i (no generic "limit exhausted")
     expect(classifyFailoverReason("LLM error: weekly/monthly limit reached")).toBe("rate_limit");
   });
   it("classifies permanent auth errors as auth_permanent", () => {