[idd] transport: abstract LGMP implementation

Introduce transport, frame, and control interfaces with an LGMP factory
backend.

Move LGMP and IVSHMEM implementation details under transport/lgmp and
expose direct frame-buffer memory through a neutral capability.

idd/LGIdd/transport/lgmp/CLGMPTransport.h

@@ -0,0 +1,56 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#pragma once
+
+#include "transport/ITransport.h"
+#include "transport/lgmp/CIVSHMEM.h"
+#include "transport/lgmp/CLGMPControl.h"
+#include "transport/lgmp/CLGMPFrameTransport.h"
+#include "transport/lgmp/CLGMPHost.h"
+
+class CLGMPTransport final : public ITransport
+{
+private:
+  // Keep this declaration order. Destruction must release frame and control
+  // allocations before the LGMP host and its IVSHMEM mapping are destroyed.
+  CIVSHMEM            m_ivshmem;
+  CLGMPHost           m_host;
+  CLGMPControl        m_control;
+  CLGMPFrameTransport m_frames;
+
+public:
+  CLGMPTransport();
+  ~CLGMPTransport() override = default;
+
+  CLGMPTransport(const CLGMPTransport&) = delete;
+  CLGMPTransport& operator=(const CLGMPTransport&) = delete;
+
+  OpenResult Open() override;
+  bool Initialize() override;
+  bool Setup(size_t alignment) override;
+  void Process(ITransportEvents& events) override;
+
+  FrameMemoryLimits GetMemoryLimits() const override;
+  DirectFrameBufferMemory GetDirectMemory() const override;
+
+  IFrameTransport& Frames() override { return m_frames; }
+  IControlTransport& Control() override { return m_control; }
+};