ADR 0046 — the installer fetches what it pins

The blocking question was where a container image comes from, and the version
that blocked assumed the machine might have no network. That assumption came
from the LAB: a scenario is a closed address space by design, which is what lets
two scenarios hold the same addresses without meeting. Production is not sealed
— a machine being adopted has a network, and one that does not is a machine
where very little works anyway.

So substrate.lock carries references, not payload: an image name and a digest,
fetched at apply time. A first node pulls from upstream because no mesh registry
exists yet; every node after that pulls from the mesh's own. The lab is the
exception and places images itself, the way it already places the host binary —
a property of a test environment, and letting it dictate the production design
would be the tail wagging the dog.

Pinned by DIGEST rather than tag. Reproducibility comes from pinning the
identity of a thing, not from carrying its bytes, which is what makes fetching
acceptable rather than a compromise.

ADR 0041 survives untouched, which was the point. "Copy it onto a machine and
run it" stays literally true — one binary, a few megabytes, which then fetches
what it was told to. Carrying images would have quietly redefined the property
that decision rests on.

Costs accepted and named: an apply can now fail because something is
unreachable, which a self-contained artifact could not, so it must fail legibly
— naming what it could not fetch and from where. And the lab needs a way to
place images into a machine that also has no container runtime, both of which
are lab-installation concerns and neither solved here.

Research 012's build-time-versus-apply-time reframing narrows accordingly: it
still holds for what a tailored installer contains, and no longer has to hold
for images.

01-RESEARCH/012-the-minimum-viable-node/00-overview.md

@@ -34,6 +34,11 @@ carry everything in the bundle, download at apply time, or have something push t
 first. Downloading fails on the first node, which cannot fetch the image registry from the image
 registry it is trying to start.
 
+> **Qualified by [ADR 0046](../../02-DECISIONS/0046-the-installer-fetches-what-it-pins.md).** The
+> reframing below still holds for what a *tailored installer* contains — the missing pieces for a
+> given machine. It does **not** have to hold for container images: the installer fetches those
+> by digest, because a real machine has a network and the sealed case is the lab.
+
 **The reframing:** the machine is not offline. What matters is *when* the fetching happens. Move
 it from apply time to **build time** — build the installer on a machine that has a network,
 tailored to the target, and apply it on a target that then needs nothing. That is the same move