os.pathsep, os.access + F_OK/R_OK/W_OK/X_OK, socket.gethostname()

Found missing 2026-10-19 in sysdash's backend.py. Its PATH search is any(os.access(os.path.join(d, "nvidia-smi"), os.X_OK) for d in os.environ.get("PATH", "").split(os.pathsep)), and it labels each sample with the host name. All three were undefined variable (os) / missing.

Fix:

• os.pathsep is ':', next to os.sep.
• The *_OK constants use the POSIX values.
• os.access → pyos_access → PyPalAccessMode. ESP has no access() and FAT has no permission bits, so there it only checks that the path exists.
• socket.gethostname() returns uname's nodename (mimic_socket.pas). It raises OSError on an ESP, which has no uname.

Test: test/test_nilpy_os_access_pathsep_gethostname.npy.