fix: recognize Venice 402 billing errors for model fallback

Venice returns "Insufficient USD or Diem balance" which has extra
words between "insufficient" and "balance", causing the billing
pattern `"insufficient balance"` (substring match) to miss it.

Change the pattern to a regex `/insufficient\b.*\bbalance/i` so
providers that insert qualifier words (e.g. "USD or Diem") between
"insufficient" and "balance" are still classified as billing errors
and trigger model fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -106,6 +106,9 @@ describe("isBillingErrorMessage", () => {
       "Payment Required",
       "HTTP 402 Payment Required",
       "plans & billing",
+      // Venice returns "Insufficient USD or Diem balance" which has extra words
+      // between "insufficient" and "balance" (#XXXXX)
+      "Insufficient USD or Diem balance to complete request. Visit https://venice.ai/settings/api to add credits.",
     ];
     for (const sample of samples) {
       expect(isBillingErrorMessage(sample)).toBe(true);
@@ -650,6 +653,12 @@ describe("classifyFailoverReason", () => {
     expect(classifyFailoverReason(TOGETHER_ENGINE_OVERLOADED_MESSAGE)).toBe("overloaded");
     expect(classifyFailoverReason(GROQ_TOO_MANY_REQUESTS_MESSAGE)).toBe("rate_limit");
     expect(classifyFailoverReason(GROQ_SERVICE_UNAVAILABLE_MESSAGE)).toBe("overloaded");
+    // Venice 402 billing error with extra words between "insufficient" and "balance"
+    expect(
+      classifyFailoverReason(
+        "Insufficient USD or Diem balance to complete request. Visit https://venice.ai/settings/api to add credits.",
+      ),
+    ).toBe("billing");
   });
 
   it("classifies internal and compatibility error messages", () => {

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

@@ -51,7 +51,7 @@ const ERROR_PATTERNS = {
     /insufficient[_ ]quota/i,
     "credit balance",
     "plans & billing",
-    "insufficient balance",
+    /insufficient\b.*\bbalance/i,
   ],
   authPermanent: [
     /api[_ ]?key[_ ]?(?:revoked|invalid|deactivated|deleted)/i,