Server.buffer(named:)

Runs in a process of its own even on a connected server, so that the answer does not depend on which mode asked. A connection reports a command's output as *lines*, and show-buffer writes the buffer as bytes with a terminator after them — so a buffer ending in a newline and one that does not arrive in the same shape as a listing whose last row is empty. Nothing on the wire tells the two apart, and every supported tmux behaves this way, so the bytes are read from a process instead of guessed at.