fix(mcp): use json.RawMessage for proper JSON unmarshaling

Add RawMessage type alias to modules/json and use it in MCP handler.
The custom RawMessage type was not implementing json.Unmarshaler,
causing parse errors when receiving MCP tool calls with params object.

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

modules/json/json.go

@@ -109,3 +109,7 @@ func UnmarshalHandleDoubleEncode(bs []byte, v any) error {
 	}
 	return err
 }
+
+// RawMessage is a raw encoded JSON value.
+// It implements Marshaler and Unmarshaler and can be used to delay JSON decoding.
+type RawMessage = json.RawMessage

routers/api/v2/mcp.go

@@ -22,16 +22,13 @@ import (
 	"code.gitea.io/gitea/services/context"
 )
 
-// RawMessage is a raw encoded JSON value (equivalent to encoding/json.RawMessage)
-type RawMessage []byte
-
 // MCP Protocol Types (JSON-RPC 2.0)
 
 type MCPRequest struct {
-	JSONRPC string     `json:"jsonrpc"`
-	ID      any        `json:"id"`
-	Method  string     `json:"method"`
-	Params  RawMessage `json:"params,omitempty"`
+	JSONRPC string          `json:"jsonrpc"`
+	ID      any             `json:"id"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params,omitempty"`
 }
 
 type MCPResponse struct {