feat: add `_meta` field to `CallToolRequestParams` per MCP protocol

Support the protocol-reserved `_meta` parameter for tool invocations, enabling metadata (e.g., progressToken, identityToken) transmission as specified in MCP spec.

See: https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/docs/specification/draft/basic/index.mdx#general-fields

api/core/mcp/auth_client.py

@@ -174,7 +174,7 @@ class MCPClientWithAuthRetry(MCPClient):
         """
         return self._execute_with_retry(super().list_tools)
 
-    def invoke_tool(self, tool_name: str, tool_args: dict[str, Any]) -> CallToolResult:
+    def invoke_tool(self, tool_name: str, tool_args: dict[str, Any], _meta: dict[str, Any]) -> CallToolResult:
         """
         Invoke a tool on the MCP server with auth retry.
 
@@ -188,4 +188,4 @@ class MCPClientWithAuthRetry(MCPClient):
         Raises:
             MCPAuthError: If authentication fails after retries
         """
-        return self._execute_with_retry(super().invoke_tool, tool_name, tool_args)
+        return self._execute_with_retry(super().invoke_tool, tool_name, tool_args, _meta)

api/core/mcp/mcp_client.py

@@ -96,11 +96,11 @@ class MCPClient:
         response = self._session.list_tools()
         return response.tools
 
-    def invoke_tool(self, tool_name: str, tool_args: dict[str, Any]) -> CallToolResult:
+    def invoke_tool(self, tool_name: str, tool_args: dict[str, Any], _meta: dict[str, Any]) -> CallToolResult:
         """Call a tool"""
         if not self._session:
             raise ValueError("Session not initialized.")
-        return self._session.call_tool(tool_name, tool_args)
+        return self._session.call_tool(tool_name, tool_args, _meta=_meta)
 
     def cleanup(self):
         """Clean up resources"""

api/core/mcp/session/client_session.py

@@ -248,6 +248,7 @@ class ClientSession(
         self,
         name: str,
         arguments: dict[str, Any] | None = None,
+        _meta: dict[str, Any] | None = None,
         read_timeout_seconds: timedelta | None = None,
     ) -> types.CallToolResult:
         """Send a tools/call request."""
@@ -256,7 +257,7 @@ class ClientSession(
             types.ClientRequest(
                 types.CallToolRequest(
                     method="tools/call",
-                    params=types.CallToolRequestParams(name=name, arguments=arguments),
+                    params=types.CallToolRequestParams(name=name, arguments=arguments, _meta=_meta),
                 )
             ),
             types.CallToolResult,

api/core/mcp/types.py

@@ -855,6 +855,7 @@ class CallToolRequestParams(RequestParams):
 
     name: str
     arguments: dict[str, Any] | None = None
+    _meta: dict[str, Any] | None = None
     model_config = ConfigDict(extra="allow")
 
 

api/core/tools/mcp_tool/tool.py

@@ -49,13 +49,7 @@ class MCPTool(Tool):
         message_id: str | None = None,
         inputs: dict[str, Any] | None = None,
     ) -> Generator[ToolInvokeMessage, None, None]:
-        # If inputs is provided, flatten its key/value pairs into the tool_parameters.
-        # This is a conservative merge: only add a key from inputs if it does not already exist in tool_parameters.
-        if inputs:
-            for key, value in inputs.items():
-                if key not in tool_parameters:
-                    tool_parameters[key] = value
-        result = self.invoke_remote_mcp_tool(tool_parameters)
+        result = self.invoke_remote_mcp_tool(tool_parameters, _meta=inputs)
         # handle dify tool output
         for content in result.content:
             if isinstance(content, TextContent):
@@ -139,7 +133,7 @@ class MCPTool(Tool):
             if value is not None and not (isinstance(value, str) and value.strip() == "")
         }
 
-    def invoke_remote_mcp_tool(self, tool_parameters: dict[str, Any]) -> CallToolResult:
+    def invoke_remote_mcp_tool(self, tool_parameters: dict[str, Any], _meta: dict[str, Any]) -> CallToolResult:
         headers = self.headers.copy() if self.headers else {}
         tool_parameters = self._handle_none_parameter(tool_parameters)
 
@@ -174,7 +168,8 @@ class MCPTool(Tool):
                 sse_read_timeout=self.sse_read_timeout,
                 provider_entity=provider_entity,
             ) as mcp_client:
-                return mcp_client.invoke_tool(tool_name=self.entity.identity.name, tool_args=tool_parameters)
+                return mcp_client.invoke_tool(tool_name=self.entity.identity.name, tool_args=tool_parameters, 
+                                              _meta=_meta)
         except MCPConnectionError as e:
             raise ToolInvokeError(f"Failed to connect to MCP server: {e}") from e
         except Exception as e: