The nvmeof (spdk-target) service carried a versioned bootstrap mount
(type: image, source ${OCI_IMAGE}:${IMAGE_VERSION} -> /artifacts) plus an
IMAGE_VERSION env. Bumping IMAGE_VERSION therefore changed the service config,
so `docker compose up -d` recreated the container -> nvmf_tgt restarted ->
every connected host's NVMe/TCP root dropped at once. That is precisely the
fleet-wide outage the long-lived-target design exists to prevent.
Remove the /artifacts image-volume and IMAGE_VERSION env from nvmeof so its
config no longer depends on the version — compose leaves it running across a
bump. Bootstrap and rolling updates are already fully covered by spdk-loader
(stages the current release into ./spdk/releases and adds it online via
JSON-RPC); spdk-target.sh's seed block is guarded, so it just no-ops when
/artifacts isn't mounted. Verified nvmeof no longer references IMAGE_VERSION
(only spdk-loader does); compose YAML validates.
BENCH-VERIFY: bump IMAGE_VERSION + up -d with a host connected -> nvmeof
container not recreated, host root survives, loader adds the new version.