Checkpoint 2: integrate native Editor, MCP, gameplay builds and standalone export

include/faset/editor/mcp.hpp

@@ -0,0 +1,32 @@
+#pragma once
+#include <faset/editor/commands.hpp>
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace faset::editor {
+// MCP is compiled exclusively into the Editor / headless authoring executable.
+class McpServer {
+  public:
+    explicit McpServer(Commands& commands) : commands_(commands) {}
+    std::optional<Json> handle(const Json& message);
+    Json parse_error() const;
+
+  private:
+    Commands& commands_;
+    bool initialized_ = false, ready_ = false;
+};
+class StdioTransport {
+  public:
+    // Nonblocking: GUI and MCP can share the same authoring session and event loop.
+    std::vector<std::string> poll();
+    bool closed() const noexcept {
+        return closed_;
+    }
+    void send(const Json& message);
+
+  private:
+    std::string buffer_;
+    bool closed_ = false;
+};
+} // namespace faset::editor