fix(failover): disambiguate periodic limit errors

src/agents/failover-error.test.ts

@@ -123,6 +123,19 @@ describe("failover-error", () => {
         message: ZHIPUAI_WEEKLY_MONTHLY_LIMIT_EXHAUSTED_MESSAGE,
       }),
     ).toBe("rate_limit");
+    expect(
+      resolveFailoverReasonFromError({
+        message: "LLM error: monthly limit reached",
+      }),
+    ).toBe("rate_limit");
+  });
+
+  it("keeps raw-text 402 weekly/monthly limit errors in billing", () => {
+    expect(
+      resolveFailoverReasonFromError({
+        message: "402 Payment Required: Weekly/Monthly Limit Exhausted",
+      }),
+    ).toBe("billing");
   });
 
   it("infers format errors from error messages", () => {

src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts

@@ -540,6 +540,9 @@ describe("classifyFailoverReason", () => {
     expect(
       classifyFailoverReason("HTTP 402 payment required. Your limit exhausted for this plan."),
     ).toBe("billing");
+    expect(classifyFailoverReason("402 Payment Required: Weekly/Monthly Limit Exhausted")).toBe(
+      "billing",
+    );
     expect(classifyFailoverReason(INSUFFICIENT_QUOTA_PAYLOAD)).toBe("billing");
     expect(classifyFailoverReason("deadline exceeded")).toBe("timeout");
     expect(classifyFailoverReason("request ended without sending any chunks")).toBe("timeout");
@@ -595,8 +598,10 @@ 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")
+    // Independent coverage for broader periodic limit patterns.
     expect(classifyFailoverReason("LLM error: weekly/monthly limit reached")).toBe("rate_limit");
+    expect(classifyFailoverReason("LLM error: monthly limit reached")).toBe("rate_limit");
+    expect(classifyFailoverReason("LLM error: daily limit exceeded")).toBe("rate_limit");
   });
   it("classifies permanent auth errors as auth_permanent", () => {
     expect(classifyFailoverReason("invalid_api_key")).toBe("auth_permanent");

src/agents/pi-embedded-helpers/errors.ts

@@ -8,6 +8,7 @@ import {
   isAuthPermanentErrorMessage,
   isBillingErrorMessage,
   isOverloadedErrorMessage,
+  isPeriodicUsageLimitErrorMessage,
   isRateLimitErrorMessage,
   isTimeoutErrorMessage,
   matchesFormatErrorPattern,
@@ -842,6 +843,9 @@ export function classifyFailoverReason(raw: string): FailoverReason | null {
   if (isJsonApiInternalServerError(raw)) {
     return "timeout";
   }
+  if (isPeriodicUsageLimitErrorMessage(raw)) {
+    return isBillingErrorMessage(raw) ? "billing" : "rate_limit";
+  }
   if (isRateLimitErrorMessage(raw)) {
     return "rate_limit";
   }

src/agents/pi-embedded-helpers/failover-matches.ts

@@ -1,5 +1,8 @@
 type ErrorPattern = RegExp | string;
 
+const PERIODIC_USAGE_LIMIT_RE =
+  /\b(?:daily|weekly|monthly)(?:\/(?:daily|weekly|monthly))* (?:usage )?limit(?:s)?(?: (?:exhausted|reached|exceeded))?\b/i;
+
 const ERROR_PATTERNS = {
   rateLimit: [
     /rate[_ ]limit|too many requests|429/,
@@ -9,7 +12,6 @@ const ERROR_PATTERNS = {
     "quota exceeded",
     "resource_exhausted",
     "usage limit",
-    /weekly\/monthly limit/i,
     /\btpm\b/i,
     "tokens per minute",
   ],
@@ -118,6 +120,10 @@ export function isTimeoutErrorMessage(raw: string): boolean {
   return matchesErrorPatterns(raw, ERROR_PATTERNS.timeout);
 }
 
+export function isPeriodicUsageLimitErrorMessage(raw: string): boolean {
+  return PERIODIC_USAGE_LIMIT_RE.test(raw);
+}
+
 export function isBillingErrorMessage(raw: string): boolean {
   const value = raw.toLowerCase();
   if (!value) {