refactor: replace mcp-go with the official MCP Go SDK (#223)

## Summary

Replace `github.com/mark3labs/mcp-go` with the official
`github.com/modelcontextprotocol/go-sdk v1.7.0`.

All 54 existing tools, scopes, CLI, `stdio` and HTTP (`/mcp`) modes, and
per-request authentication remain supported. This PR is limited to the SDK
equivalence migration; the stateless 2026 HTTP transport is deferred to a
follow-up PR.

## Verification

- Tool definitions were compared with `main` and matched for all 54 tools.
- `make lint`, `make fmt`, `go test -count=1 -race ./...`, `make build`, and
  `make tidy` pass.

---------

Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/223
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

pkg/tool/handler_test.go

@@ -0,0 +1,105 @@
+package tool
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"testing"
+
+	"github.com/modelcontextprotocol/go-sdk/jsonrpc"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+func callTool(handler Handler, arguments json.RawMessage) (*mcp.CallToolResult, error) {
+	serverTool := ServerTool{Tool: &mcp.Tool{Name: "example"}, Handler: handler}
+	return serverTool.MCPHandler()(context.Background(), &mcp.CallToolRequest{
+		Params: &mcp.CallToolParamsRaw{Arguments: arguments},
+	})
+}
+
+func captureArguments(into *map[string]any) Handler {
+	return func(_ context.Context, arguments map[string]any) (*mcp.CallToolResult, error) {
+		*into = arguments
+		return &mcp.CallToolResult{}, nil
+	}
+}
+
+func TestMCPHandler(t *testing.T) {
+	var got map[string]any
+	result, err := callTool(captureArguments(&got), json.RawMessage(`{"count":2,"nested":{"enabled":true}}`))
+	if err != nil {
+		t.Fatalf("MCPHandler() error = %v", err)
+	}
+	if result == nil {
+		t.Fatal("MCPHandler() result is nil")
+	}
+	if got["count"] != float64(2) {
+		t.Errorf("count type/value = %T(%v), want float64(2)", got["count"], got["count"])
+	}
+}
+
+func TestMCPHandlerRejectsInvalidArguments(t *testing.T) {
+	called := false
+	handler := func(context.Context, map[string]any) (*mcp.CallToolResult, error) {
+		called = true
+		return &mcp.CallToolResult{}, nil
+	}
+
+	for _, arguments := range []json.RawMessage{json.RawMessage(`[]`), json.RawMessage(`"text"`), json.RawMessage(`{"broken"`)} {
+		_, err := callTool(handler, arguments)
+		assertProtocolErrorCode(t, err, jsonrpc.CodeInvalidParams)
+	}
+	if called {
+		t.Fatal("handler was called with invalid arguments")
+	}
+}
+
+// Tools without parameters are callable with an omitted or null "arguments",
+// which is what clients send and what mcp-go accepted before the SDK migration.
+func TestMCPHandlerAcceptsAbsentArguments(t *testing.T) {
+	for _, arguments := range []json.RawMessage{nil, json.RawMessage(`null`)} {
+		var got map[string]any
+		if _, err := callTool(captureArguments(&got), arguments); err != nil {
+			t.Fatalf("MCPHandler() with arguments %s error = %v", arguments, err)
+		}
+		if got == nil || len(got) != 0 {
+			t.Errorf("arguments = %#v, want an empty map", got)
+		}
+	}
+}
+
+func TestMCPHandlerConvertsErrorsAndRecoversPanics(t *testing.T) {
+	for _, test := range []struct {
+		name    string
+		handler Handler
+	}{
+		{
+			name: "handler error",
+			handler: func(context.Context, map[string]any) (*mcp.CallToolResult, error) {
+				return nil, errors.New("failed")
+			},
+		},
+		{
+			name: "panic",
+			handler: func(context.Context, map[string]any) (*mcp.CallToolResult, error) {
+				panic("failed")
+			},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			_, err := callTool(test.handler, nil)
+			assertProtocolErrorCode(t, err, jsonrpc.CodeInternalError)
+		})
+	}
+}
+
+func assertProtocolErrorCode(t *testing.T, err error, want int64) {
+	t.Helper()
+	var protocolErr *jsonrpc.Error
+	if !errors.As(err, &protocolErr) {
+		t.Fatalf("error = %v, want *jsonrpc.Error", err)
+	}
+	if protocolErr.Code != want {
+		t.Errorf("error code = %d, want %d", protocolErr.Code, want)
+	}
+}