feat(cliproxy): add provider error detection for composite fallback

- Add PROVIDER_ERROR_PATTERNS for HTTP 4xx/5xx, overloaded, quota, rate limit
- Add detectFailedTier() to identify which composite tier failed from stderr
- Add isProviderError() to distinguish provider failures from normal exits

src/cliproxy/executor/retry-handler.ts

@@ -11,6 +11,7 @@
 import { fail, warn, info } from '../../utils/ui';
 import { CLIProxyProvider } from '../types';
 import { handleBanDetection } from '../account-safety';
+import { CompositeTierConfig } from '../../config/unified-config-types';
 
 /**
  * Check if error is network-related
@@ -98,3 +99,30 @@ export async function handleQuotaCheck(provider: CLIProxyProvider): Promise<void
     }
   }
 }
+
+/** Error patterns indicating provider failure */
+export const PROVIDER_ERROR_PATTERNS = [
+  /Error:\s*4[012][0-9]/i,
+  /Error:\s*5[0-9]{2}/i,
+  /overloaded/i,
+  /quota.*exceeded/i,
+  /ECONNREFUSED/i,
+  /rate.?limit/i,
+];
+
+/** Detect which composite tier failed from stderr output */
+export function detectFailedTier(
+  stderr: string,
+  tiers: { opus: CompositeTierConfig; sonnet: CompositeTierConfig; haiku: CompositeTierConfig }
+): 'opus' | 'sonnet' | 'haiku' | null {
+  for (const tier of ['opus', 'sonnet', 'haiku'] as const) {
+    if (stderr.includes(tiers[tier].model)) return tier;
+  }
+  return null;
+}
+
+/** Check if Claude exit indicates provider error (vs normal user exit) */
+export function isProviderError(exitCode: number, stderr: string): boolean {
+  if (exitCode === 0) return false;
+  return PROVIDER_ERROR_PATTERNS.some((p) => p.test(stderr));
+}