The directory berths live in: $XDG_RUNTIME_DIR/calypso when the runtime
directory is set (Linux, per-user 0700, cleared on logout), else the system
temp directory (macOS TMPDIR is already per-user-private; Linux /tmp).
Returns string
The absolute berth directory path (not guaranteed to exist yet).
The directory berths live in:
$XDG_RUNTIME_DIR/calypsowhen the runtime directory is set (Linux, per-user0700, cleared on logout), else the system temp directory (macOSTMPDIRis already per-user-private; Linux/tmp).