refactor(provider): simplify LiteLLM requester usage handling

- Remove unused Anthropic-specific tool schema generation
  - Share completion argument construction between normal and streaming calls
  - Use LiteLLM/OpenAI native usage fields for monitoring
  - Collect stream token usage from LiteLLM stream_options
  - Update LiteLLM requester tests for unified usage fields

src/langbot/pkg/provider/modelmgr/requesters/litellmchat.py

@@ -88,17 +88,11 @@ class LiteLLMRequester(requester.ProviderAPIRequester):
     def _extract_usage(self, response) -> dict:
         """Extract usage info from LiteLLM response."""
         usage = response.usage
-        usage_info = {
+        return {
             'prompt_tokens': usage.prompt_tokens or 0,
             'completion_tokens': usage.completion_tokens or 0,
             'total_tokens': usage.total_tokens or 0,
         }
-        # TODO: LangBot internal inconsistency - LLM monitoring uses input_tokens/output_tokens,
-        # while embedding monitoring uses prompt_tokens. Should unify in requester.py to use
-        # prompt_tokens (OpenAI native) consistently. After that, remove these compatibility aliases.
-        usage_info['input_tokens'] = usage_info['prompt_tokens']
-        usage_info['output_tokens'] = usage_info['completion_tokens']
-        return usage_info
 
     def _build_common_args(self, args: dict, include_retry_params: bool = True) -> dict:
         """Apply common requester config to args dict."""
@@ -136,6 +130,37 @@ class LiteLLMRequester(requester.ProviderAPIRequester):
             raise errors.RequesterError(f'API 错误: {str(e)}')
         raise errors.RequesterError(f'未知错误: {str(e)}')
 
+    async def _build_completion_args(
+        self,
+        model: requester.RuntimeLLMModel,
+        messages: typing.List[provider_message.Message],
+        funcs: typing.List[resource_tool.LLMTool] = None,
+        extra_args: dict[str, typing.Any] = {},
+        stream: bool = False,
+    ) -> dict:
+        """Build common completion arguments for invoke_llm and invoke_llm_stream."""
+        req_messages = self._convert_messages(messages)
+        model_name = self._build_litellm_model_name(model.model_entity.name)
+        api_key = model.provider.token_mgr.get_token()
+
+        args = {
+            'model': model_name,
+            'messages': req_messages,
+            'api_key': api_key,
+        }
+        if stream:
+            args['stream'] = True
+            args['stream_options'] = {'include_usage': True}
+        self._build_common_args(args)
+        args.update(extra_args)
+
+        if funcs:
+            tools = await self.ap.tool_mgr.generate_tools_for_openai(funcs)
+            if tools:
+                args['tools'] = tools
+
+        return args
+
     async def invoke_llm(
         self,
         query: pipeline_query.Query,
@@ -146,25 +171,7 @@ class LiteLLMRequester(requester.ProviderAPIRequester):
         remove_think: bool = False,
     ) -> tuple[provider_message.Message, dict]:
         """Invoke LLM and return message with usage info."""
-        # DO NOT modify input messages - copy them
-        req_messages = self._convert_messages(messages)
-
-        model_name = self._build_litellm_model_name(model.model_entity.name)
-
-        api_key = model.provider.token_mgr.get_token()
-
-        args = {
-            'model': model_name,
-            'messages': req_messages,
-            'api_key': api_key,
-        }
-        self._build_common_args(args)
-        args.update(extra_args)
-
-        if funcs:
-            tools = await self.ap.tool_mgr.generate_tools_for_openai(funcs)
-            if tools:
-                args['tools'] = tools
+        args = await self._build_completion_args(model, messages, funcs, extra_args, stream=False)
 
         try:
             response = await acompletion(**args)
@@ -198,24 +205,7 @@ class LiteLLMRequester(requester.ProviderAPIRequester):
         remove_think: bool = False,
     ) -> provider_message.MessageChunk:
         """Invoke LLM streaming and yield chunks."""
-        req_messages = self._convert_messages(messages)
-
-        model_name = self._build_litellm_model_name(model.model_entity.name)
-        api_key = model.provider.token_mgr.get_token()
-
-        args = {
-            'model': model_name,
-            'messages': req_messages,
-            'api_key': api_key,
-            'stream': True,
-        }
-        self._build_common_args(args)
-        args.update(extra_args)
-
-        if funcs:
-            tools = await self.ap.tool_mgr.generate_tools_for_openai(funcs)
-            if tools:
-                args['tools'] = tools
+        args = await self._build_completion_args(model, messages, funcs, extra_args, stream=True)
 
         chunk_idx = 0
         role = 'assistant'
@@ -223,6 +213,19 @@ class LiteLLMRequester(requester.ProviderAPIRequester):
         try:
             response = await acompletion(**args)
             async for chunk in response:
+                # Check for usage chunk (final chunk with stream_options include_usage)
+                if hasattr(chunk, 'usage') and chunk.usage and (not hasattr(chunk, 'choices') or not chunk.choices):
+                    usage_info = {
+                        'prompt_tokens': chunk.usage.prompt_tokens or 0,
+                        'completion_tokens': chunk.usage.completion_tokens or 0,
+                        'total_tokens': chunk.usage.total_tokens or 0,
+                    }
+                    if query:
+                        if query.variables is None:
+                            query.variables = {}
+                        query.variables['_stream_usage'] = usage_info
+                    continue
+
                 if not hasattr(chunk, 'choices') or not chunk.choices:
                     continue