Add MCP integration with MCPServer for tool-based interactions

- Introduce `MCPServer` to support connecting to MCP servers via stdio, SSE, or HTTP.
- Implement tool fetching, management, and invocation through MCP.
- Add `WithMCPServer` method to `ToolBox` for seamless tool integration.
- Extend schema package to handle raw JSON schemas for MCP tools.
- Update documentation with MCP usage guidelines and examples.

toolbox.go

@@ -2,6 +2,7 @@ package llm
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 )
@@ -11,6 +12,7 @@ import (
 // the correct parameters.
 type ToolBox struct {
 	functions       map[string]Function
+	mcpServers      map[string]*MCPServer // tool name -> MCP server that provides it
 	dontRequireTool bool
 }
 
@@ -91,6 +93,18 @@ var (
 )
 
 func (t ToolBox) executeFunction(ctx *Context, functionName string, params string) (any, error) {
+	// Check if this is an MCP tool
+	if server, ok := t.mcpServers[functionName]; ok {
+		var args map[string]any
+		if params != "" {
+			if err := json.Unmarshal([]byte(params), &args); err != nil {
+				return nil, fmt.Errorf("failed to parse MCP tool arguments: %w", err)
+			}
+		}
+		return server.CallTool(ctx, functionName, args)
+	}
+
+	// Regular function
 	f, ok := t.functions[functionName]
 
 	if !ok {