Installed Alpine disk fails to mount the 9p work share on every boot

[NovusEdge]

Every boot of an installed Alpine disk VM prints:

fsck: fsck.9p: No such file or directory
mount: mounting work on /work failed: No such file or directory
 * Some local filesystem failed to mount   [ !! ]

The share is exported by QEMU (-virtfs local,path=~/.stoat/shared/<vm>,mount_tag=work) and the guest carries an fstab entry for it, so localmount tries and fails. Two causes are visible in the output: fsck has no fsck.9p helper and runs anyway, and the mount point does not exist on the installed root.

The install log shows the same shape earlier: umount: can't unmount /mnt/work: No such file or directory.

Reproduce with stoat create X --image alpine-standard --mode disk, stoat up X, then read the console. The failure is not fatal, and openrc marks local filesystems degraded on every boot.

Related: #42 made the shares mount on every boot and dropped _netdev so openrc's localmount runs them. The fstab entry needs passno=0 so fsck skips it, and the mount point needs creating before localmount.

Found while clearing the needs-live-boot debt on #48.

[NovusEdge]

Root cause, found while planning the fix.

Neither Go writer is at fault. apkovl.Mount9p.FstabLine() (internal/apkovl/mount9p.go:45) already emits work /mnt/work 9p <opts> 0 0 and creates the mountpoint, and both callers (apkovl.go:211, sshx/sharemount.go:40) render through it.

The broken entry comes from setup-disk. It mounts the target root on /mnt, which is the same directory stoat mounts its 9p shares under. The installer's fstab generator therefore sees /mnt/work as a filesystem belonging to the new root and copies it onto the target as work /work 9p ... 0 2, with a passno of 2 and a mountpoint that does not exist there.

sshx cannot paper over it either: shareMountTags returns nothing unless v.Share is set, and it runs after the boot-time mount has already failed.

So the fix belongs in the install script, which repairs the target's fstab before powering off. No Go writer changes.