Expand description
Process tree walker. Given a tmux pane PID, find the most recently
spawned claude or codex descendant so we can read its cwd and
report it as the agent’s working directory.
sysinfo abstracts /proc on Linux and libproc on macOS, so the same
code path works on both. We refresh with a minimal ProcessRefreshKind
(only the fields we read) to keep the cost low — refreshing all
processes every tick is sub-millisecond on typical workstations.