The controlled side already answers a refused port-forward channel with
opened { success: false, message }; on the multiplexed path TunnelHandle::
on_frame only logged that message at debug and closed the channel, so the
user saw a closed connection with no explanation, worst on the RDP path
where only the RDP client's own error remained. on_frame now returns the
message the window should show, deduplicated per distinct reason (capped
at MAX_REPORTED_OPEN_ERRORS) so one page load's dozen refused connections
surface one dialog per reason instead of a dozen.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EZ49AbZJYfm8NTp5yDPMab