fix(combo): add 429 to PROVIDER_FAILURE_ERROR_CODES to prevent infinite retry loop

open-sse/services/accountFallback.ts

@@ -78,12 +78,12 @@ function toJsonRecord(value: unknown): JsonRecord {
 }
 
 // Provider-level failure tracking for circuit breaker behavior
-// Error codes that count toward provider-level failure threshold
-// 429 (rate limit) is intentionally excluded: rate limits are connection-scoped
-// and handled via Connection Cooldown, not provider-wide circuit breaker.
-// Counting 429 toward provider failure causes cascading provider trips at scale
-// when many connections hit rate limits simultaneously (Issue #1846).
-const PROVIDER_FAILURE_ERROR_CODES = new Set([408, 500, 502, 503, 504]);
+// Error codes that count toward provider-level failure threshold.
+// 429 is included: per-error-type cooldowns (rate_limit: 60s, quota_exhausted: 1h)
+// prevent cascading provider trips at scale (Issue #1846 concern addressed),
+// while still allowing the circuit breaker to open on sustained 429s and
+// prevent infinite combo retries (Issue #3200).
+const PROVIDER_FAILURE_ERROR_CODES = new Set([408, 429, 500, 502, 503, 504]);
 
 // Per-connection failure deduplication: prevents rapid-fire failures from the
 // same connection from counting multiple times toward the provider breaker.

src/sse/handlers/chat.ts

@@ -173,7 +173,7 @@ function intersectAllowedConnectionIds(primary: unknown, secondary: unknown): st
   return first || second || null;
 }
 
-const PROVIDER_BREAKER_FAILURE_STATUSES = new Set([408, 500, 502, 503, 504]);
+const PROVIDER_BREAKER_FAILURE_STATUSES = new Set([408, 429, 500, 502, 503, 504]);
 
 /**
  * Handle chat completion request

tests/unit/account-fallback-service.test.ts

@@ -536,7 +536,7 @@ test("recordModelLockoutFailure uses provider profile cooldowns, backoff, and re
 
 // Provider-level failure circuit breaker tests
 test("isProviderFailureCode correctly identifies provider-wide transient error codes", () => {
-  assert.equal(isProviderFailureCode(429), false);
+  assert.equal(isProviderFailureCode(429), true);
   assert.equal(isProviderFailureCode(408), true);
   assert.equal(isProviderFailureCode(500), true);
   assert.equal(isProviderFailureCode(502), true);