[idd] ipc: connect LGInput to LGIdd

Move the reusable named-pipe endpoint and shared support code into
the LGCommon static library.

Run a dedicated server in LGIdd and a reconnecting client in
LGInput, with device-lifecycle handling and report framing.

Refactor the helper pipe to use the same endpoint implementation.

idd/LGInput/ipc/CInputPipeClient.cpp

@@ -0,0 +1,93 @@
+/**
+ * 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
+ */
+
+#include "CInputPipeClient.h"
+
+#include "CDebug.h"
+#include "InputPipeProtocol.h"
+#include "../CHIDDevice.h"
+
+bool CInputPipeClient::Start()
+{
+  m_lastSequence = 0;
+  m_endpoint.SetHandler(this);
+  return m_endpoint.Start(
+    LG_INPUT_PIPE_NAME,
+    CPipeEndpoint::Mode::Client,
+    sizeof(LGInputPipeMessage));
+}
+
+void CInputPipeClient::Stop()
+{
+  const bool wasRunning = m_endpoint.IsRunning();
+  m_endpoint.Stop();
+  m_lastSequence = 0;
+  if (wasRunning)
+    CHIDDevice::ClearReports();
+}
+
+void CInputPipeClient::OnPipeConnected()
+{
+  m_lastSequence = 0;
+  DEBUG_INFO("Connected to the LGIdd input transport");
+}
+
+void CInputPipeClient::OnPipeDisconnected()
+{
+  m_lastSequence = 0;
+  CHIDDevice::ClearReports();
+  DEBUG_INFO("Disconnected from the LGIdd input transport; reconnecting");
+}
+
+bool CInputPipeClient::OnPipeMessage(
+  const void * frame,
+  size_t size)
+{
+  if (size != sizeof(LGInputPipeMessage))
+    return false;
+
+  const LGInputPipeMessage & message =
+    *static_cast<const LGInputPipeMessage *>(frame);
+  if (message.magic != LG_INPUT_PIPE_MAGIC ||
+      message.version != LG_INPUT_PIPE_VERSION ||
+      message.type != LG_INPUT_PIPE_MESSAGE_REPORT ||
+      !message.payloadSize ||
+      message.payloadSize > sizeof(message.payload))
+    return false;
+
+  if (!message.sequence ||
+      (m_lastSequence && message.sequence != m_lastSequence + 1))
+  {
+    DEBUG_WARN("LGInput pipe report sequence changed unexpectedly");
+    return false;
+  }
+  m_lastSequence = message.sequence;
+
+  const NTSTATUS status =
+    CHIDDevice::SubmitReport(message.payload, message.payloadSize);
+  if (status == STATUS_INVALID_PARAMETER)
+    return false;
+
+  if (status == STATUS_BUFFER_OVERFLOW)
+    DEBUG_WARN("LGInput HID report queue is full; dropping a report");
+  else if (!NT_SUCCESS(status) && status != STATUS_DEVICE_NOT_READY)
+    DEBUG_WARN_HR(status, "Failed to submit an LGInput HID report");
+  return true;
+}