Previously Start() only pulled when the image was missing locally
(imgErr != nil). Once a tenant's Docker daemon had `:latest` cached,
it stuck on that snapshot forever even after publish-runtime pushed
a newer image with the same tag — the same image-cache class that
sibling task #232 closed on the controlplane redeploy path.
Now Start() additionally re-pulls when the tag is "moving"
(`:latest`, no tag, `:staging`, `:main`, `:dev`, `:edge`, `:nightly`,
`:rolling`). Pinned tags (semver, sha-prefixed, date-stamped, build-id)
and digest-pinned references (`@sha256:...`) skip the pull because
their contents are by definition immutable.
The classifier (imageTagIsMoving) is deliberately conservative on the
"moving" side — only the well-known moving tags trip it. Misclassifying
a pinned tag as moving wastes bandwidth on every provision; misclassifying
moving as pinned silently bricks the fleet on stale snapshots, which
is exactly the bug class this fix closes.
Edge cases handled:
- Registry hostname with port (`localhost:5000/foo`) — the `:5000` is
not mistaken for a tag.
- Digest pinning (`image@sha256:...`) — never re-pulled even if a
moving-looking tag is also present.
- Legacy local-build tags (`workspace-template:hermes`) — treated as
pinned (no registry to move from).
Test coverage: 22 cases across all classifier shapes. No changes to
the pull-failure path (still best-effort, ContainerCreate still
surfaces the actionable "image not found" error if the pull failed
and the cache is also empty).
Task: #215. Companion to #232.
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