fix: retry different accounts on browser failure (instead of 503)

main.py

@@ -102,6 +102,22 @@ def _get_message_text(msg: Message) -> str:
     return "".join(b.text for b in c if b.text and b.type == "text")
 
 
+async def _acquire_browser():
+    """Acquire an account and get its browser, retrying different accounts on failure."""
+    last_error = ""
+    for _ in range(5):
+        account = await manager.acquire()
+        try:
+            browser = await manager.get_or_create_browser_with_retry(
+                account, headless=config.browser.headless
+            )
+            return account, browser
+        except Exception as e:
+            last_error = str(e)
+            await manager.release(account)
+    raise RuntimeError(f"All accounts failed: {last_error}")
+
+
 def verify_api_key(authorization: Optional[str] = Header(None)) -> str:
     if not authorization:
         raise HTTPException(status_code=401, detail="Missing API key")
@@ -255,11 +271,8 @@ async def chat_completions(
 
     model = request.model
 
-    account = await manager.acquire()
-
+    account, browser = await _acquire_browser()
     try:
-        browser = await manager.get_or_create_browser_with_retry(account, headless=config.browser.headless)
-
         if request.stream:
             return StreamingResponse(
                 _stream_chat_response(
@@ -534,11 +547,8 @@ async def admin_chat(request: Request, admin_key: str = Header(...)):
         prompt += f"\n\n[SYSTEM INSTRUCTION: You have access to the following tools:\n{tool_desc}\nIf you must use a tool to fulfill the request, output ONLY a JSON block wrapped in <tool_call>...</tool_call> tags, like:\n<tool_call>{{\"name\": \"tool_name\", \"arguments\": {{\"arg1\": \"value\"}} }}</tool_call>\nDo NOT output any other text if you are calling a tool.]"
         
     model = req.model
-    account = await manager.acquire()
-
+    account, browser = await _acquire_browser()
     try:
-        browser = await manager.get_or_create_browser_with_retry(account, headless=config.browser.headless)
-
         if req.stream:
             return StreamingResponse(
                 _stream_chat_response(