Upgrade VM

IV VMs run stock boldsoftware/exeuntu (which keeps Shelley) and get their tooling from provision-iv.sh in the iv-image repo. So "upgrading" a VM is normally just re-running the provisioner at a newer commit — in place, no recreate, no disk wipe, no tailnet churn.

Full destroy/recreate is now the exception, needed only when you genuinely want a fresh disk or the exe.dev-managed base has changed in a way re-provisioning can't pick up.

Path A — Re-provision in place (default)

The user provides the VM name and optionally a target tag/sha of the iv-image repo (defaults to the latest on the default branch).

One SSH command at a time — never parallel SSH to *.exe.xyz or exe.dev.