Driving a shared PTY with two real WebSocket viewers against a live instance
surfaced two defects.
Duplicated history: the server replayed the entire scrollback on every
attach, and the client appended it into an xterm that still displayed that
history. Every reconnect — backgrounded tab, laptop sleep, heartbeat timeout
— therefore added a second copy, seen as the last prompt appearing twice.
TerminalService now tracks cumulative output and serves a resume: a client
reports the offset it has rendered and receives only the gap, or a full
replay flagged reset so it clears first.
Wrong size: resize was last-writer-wins. Measured — viewer A at 80x24 had
its shell report 200x50 the moment viewer B attached on a bigger screen,
while A still drew 80 columns, so wrapped lines and full-screen programs
broke for A. TerminalViewportRegistry sizes the PTY to the per-dimension
minimum across attached viewers, the rule terminal multiplexers settled on,
and gives room back when a viewer leaves. Viewers that have not yet measured
themselves do not constrain the size.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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