test(cliproxy): add thinking suffix test and document exit 0 behavior

- Add test case for comma-separated thinking params (32768,extended)
- Add clarifying comment to isProviderError() about exit 0 handling

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));
 }