Macro eprintln_lossy 

macro_rules! eprintln_lossy {
    ($($arg:tt)*) => { ... };
}

eprintln! that can’t panic. srv’s stderr is a pipe the launcher reads, so once the launcher is gone a write fails with EPIPE (Rust ignores SIGPIPE), and eprintln! panics on a failed write. On the paths that must run when the launcher has died, the parent and stdin watchers, that panic killed the watcher thread before it could shut srv down, which left srv running with no launcher, holding srv.lock, so the app could not be opened again.