Server.capture(_:since:limit:)

Watching a pane by capturing it repeatedly sends the whole screen every time, nearly all of which the caller has already seen — which for an agent is context spent on nothing. This sends the difference.

Pass nil to start: the first read establishes where the pane is without returning its backlog, so a watcher begins at "from now on" rather than with a screenful of history. The source read is capped at 1 MiB; a wider result fails instead of allocating output the line limit would later discard.

• Parameters:
  • pane: the pane to read.
  • cursor: where the last read stopped, or nil to start watching.
  • limit: the most lines to return, keeping the newest.