_read_regular_file special-file opening

Trap: opening with O_NONBLOCK and then calling fstat() looks safe because it prevents the tested FIFO from blocking, but sockets or devices may block or trigger driver side effects before classification. Fix: classify through a race-resistant path that never performs a readable device open, reject every non-regular object, then read only the bound regular-file descriptor; keep O_NONBLOCK as defense in depth.