Function is_already_bound_error 

pub fn is_already_bound_error(err: &Error) -> bool

Classify a Listener::bind error as “another process is already bound at this name” vs any other bind failure.

AddrInUse / WouldBlock are the canonical “another listener already owns this name” signals on Unix-style transports. Windows named-pipe bind reports the same condition as PermissionDenied (ERROR_ACCESS_DENIED, raw os error 5) because the existing pipe instance’s ACL blocks the second bind. Treat that case as already-bound too — a “true” permission problem on a per-user runtime-dir socket path is extremely rare in practice (the path lives under XDG_RUNTIME_DIR / TMPDIR, always writable by the current user).