Fix LiteLLM callback leak: cache router handlers by llm_key (#4678)

skyvern/forge/sdk/api/llm/api_handler_factory.py

@@ -165,6 +165,7 @@ def _convert_allowed_fails_policy(policy: LLMAllowedFailsPolicy | None) -> Allow
 
 class LLMAPIHandlerFactory:
     _custom_handlers: dict[str, LLMAPIHandler] = {}
+    _router_handler_cache: dict[str, LLMAPIHandler] = {}
     _thinking_budget_settings: dict[str, int] | None = None
     _prompt_caching_settings: dict[str, bool] | None = None
 
@@ -389,6 +390,9 @@ class LLMAPIHandlerFactory:
 
     @staticmethod
     def get_llm_api_handler_with_router(llm_key: str) -> LLMAPIHandler:
+        if llm_key in LLMAPIHandlerFactory._router_handler_cache:
+            return LLMAPIHandlerFactory._router_handler_cache[llm_key]
+
         llm_config = LLMConfigRegistry.get_config(llm_key)
         if not isinstance(llm_config, LLMRouterConfig):
             raise InvalidLLMConfigError(llm_key)
@@ -831,6 +835,7 @@ class LLMAPIHandlerFactory:
                     LOG.error("Failed to persist artifacts", exc_info=True)
 
         llm_api_handler_with_router_and_fallback.llm_key = llm_key  # type: ignore[attr-defined]
+        LLMAPIHandlerFactory._router_handler_cache[llm_key] = llm_api_handler_with_router_and_fallback
         return llm_api_handler_with_router_and_fallback
 
     @staticmethod