Complete the bidirectional mutual exclusion between MCP remote control
and human Web viewing (§8.2). Direction 1 (remote_open rejected while a
human session holds the screen sub-connection) already existed; this adds
direction 2: a human Web viewer is now rejected while an MCP session owns
the device.
Add a m_McpTriggeredDevices marker (mirroring m_MfcTriggeredDevices) that
is set when an MCP session is created (BeginScreenCtrlOpen) and cleared at
every session-erasure site (CloseScreenCtrlSession, SweepIdleScreenCtrl,
OnScreenControlClosed, EndScreenCtrlAction), so the marker cannot go stale
and permanently block humans. HandleConnect checks IsMcpTriggered before
mutating client state or starting the remote desktop.
Co-Authored-By: deepseek-v4-pro
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