One volume can be mounted at several folders (e.g. ./shared in multiple
repos defaulting to the same volume name). Previously the daemon pidfile
and materialization cache were keyed per volume, so mounts fought over a
single daemon and shared one folder-state cache. Key both by a mount ID
(hash of the absolute folder path); blobs, journals, and the lamport
clock stay shared per volume. Content now propagates between co-mounted
folders even offline. Also default remote polling 30s -> 10s.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>