sendViewport called the associated Client.viewport, which builds the
handshake frame without RECORDING the window. A client learns its window
only from what it announced -- row_labels.len() is the window clipped to the
grid, so the two differ exactly at the bottom edge, which is where the scroll
arithmetic matters. Without the record the client cannot clamp, so every
cursor key goes upstream into Host::handle's empty vec and the arrow keys
silently do nothing.
Flagged by the improvise-bpq2 agent as the one line its work depended on and
which it could not make, web/ being another agent's ground.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EoW5BB87ZZdm96SvBTWawH
Edward Langley
145d76e7da