feat(mcp): jsonrpc envelope types and error codes

internal/mcp/jsonrpc.go

@@ -0,0 +1,43 @@
+package mcp
+
+import "encoding/json"
+
+const (
+	CodePermissionDenied = -32001
+	CodeNotFound         = -32002
+	CodeConflict         = -32003
+	CodeValidation       = -32004
+	CodeUpstreamGitea    = -32005
+)
+
+type Request struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      any             `json:"id,omitempty"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params,omitempty"`
+}
+
+type Response struct {
+	JSONRPC string    `json:"jsonrpc"`
+	ID      any       `json:"id,omitempty"`
+	Result  any       `json:"result,omitempty"`
+	Error   *RPCError `json:"error,omitempty"`
+}
+
+type RPCError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+	Data    any    `json:"data,omitempty"`
+}
+
+func NewResponse(id any, result any) Response {
+	return Response{JSONRPC: "2.0", ID: id, Result: result}
+}
+
+func NewErrorResponse(id any, code int, msg string, data any) Response {
+	return Response{
+		JSONRPC: "2.0",
+		ID:      id,
+		Error:   &RPCError{Code: code, Message: msg, Data: data},
+	}
+}