diff --git a/src/cliproxy/executor/retry-handler.ts b/src/cliproxy/executor/retry-handler.ts
index dd850450..514af33f 100644
--- a/src/cliproxy/executor/retry-handler.ts
+++ b/src/cliproxy/executor/retry-handler.ts
@@ -125,6 +125,8 @@ export function detectFailedTier(
 
 /** Check if Claude exit indicates provider error (vs normal user exit) */
 export function isProviderError(exitCode: number, stderr: string): boolean {
+  // Exit code 0 means success, even if stderr has error-like output
+  // (could be warnings, debug info, etc.)
   if (exitCode === 0) return false;
   return PROVIDER_ERROR_PATTERNS.some((p) => p.test(stderr));
 }
diff --git a/tests/unit/cliproxy/composite-fallback.test.ts b/tests/unit/cliproxy/composite-fallback.test.ts
index 919919eb..338f6a02 100644
--- a/tests/unit/cliproxy/composite-fallback.test.ts
+++ b/tests/unit/cliproxy/composite-fallback.test.ts
@@ -147,6 +147,20 @@ describe('detectFailedTier', () => {
     // Should still match because model name is substring
     expect(result).toBe('opus');
   });
+
+  it('should strip complex thinking suffix with comma-separated params', () => {
+    const tiersWithComplexBudget: typeof tiers = {
+      opus: { provider: 'agy', model: 'claude-opus-4-6-thinking(32768,extended)' },
+      sonnet: { provider: 'agy', model: 'claude-sonnet-4-5-thinking(high)' },
+      haiku: { provider: 'agy', model: 'claude-3-5-haiku' },
+    };
+
+    // Stderr contains base model name without suffix
+    const stderr = 'Error: claude-opus-4-6-thinking overloaded';
+    const result = detectFailedTier(stderr, tiersWithComplexBudget);
+    // Should match because regex strips (32768,extended) to get base name
+    expect(result).toBe('opus');
+  });
 });
 
 // ========================================