Function worker_ready_marker_path 

pub fn worker_ready_marker_path(pid: u32) -> String

Construct the ready-marker path for a worker with the given pid.

The worker uses std::process::id() (u32) as the pid source inside its own process. The host-side test reads the worker’s pid via PayloadHandle::pid(), which returns Option<u32> — Some(pid) once the child has been spawned and None before (or after a kill that tore the child down). Callers must unwrap (or propagate) the Option at the call site; this helper takes a bare u32 so the unwrap decision stays visible to the caller instead of being swallowed inside the formatter. The u32 parameter matches both the worker’s std::process::id() return type and the unwrapped payload of PayloadHandle::pid() without per-caller casts.