Function quiesce_srv 

pub async fn quiesce_srv(
    child: &mut Child,
    stdin: Option<ChildStdin>,
    graceful_timeout: Duration,
) -> Result<(ExitStatus, QuiesceOutcome)>

Stop srv and return only once it has genuinely exited — never a fixed sleep. The launcher’s one way of stopping srv: on every quit (both supervisors) and before a migration (run_migration_upgrade).

Telling srv to stop is dropping stdin, its keepalive pipe: srv reads EOF as “shut down” on every platform (bootstrap::install_shutdown_handlers) and closes every agent gracefully on the way out (agent_teardown::app_exit). Unix also gets SIGTERM, which does the same. Only if srv hasn’t exited after graceful_timeout is it force-killed — on Windows, whatever it still runs then goes with J0.