A registry inside the scenario: the mechanism, verified

Issue 009's resolution, proven manually end to end before any of it was
written.

A sealed machine pulled an image BY DIGEST from a registry on its own segment
and ran it; then the host applied all four shapes -- package, service with
boot, container from that digest, and an action inside it -- idempotently. That
is the first time the container shape has worked anywhere but a workstation,
and it was the shape blocking the whole substrate bootstrap.

The registry's digests are its own, not Docker Hub's, and that is correct
rather than a compromise: ADR 0046 requires a reference that is exact and
cannot move, and a digest this registry assigned is both. It is also not a
lab workaround -- 0048 names an OCI registry as substrate and 0046 says a first
node fetches "upstream, wherever the image ordinarily lives". This IS that
upstream, scenery in the same sense the transit router is the internet.

The base image now trusts the RFC 5737 and RFC 3849 documentation ranges as
plain-HTTP registries. Scoped to those rather than an address because they
never route on the real internet, so it cannot make a real machine trust a real
registry whatever it is copied onto.

Three faults found while verifying, two of them mine:

My probe script picked an interface with `ls /sys/class/net | head -1`, which
returns docker0 once a runtime exists -- so it addressed the wrong interface and
then, because that address overlapped the segment, broke routing on the machine
entirely. The lab itself is immune: it matches by MAC, for a related reason it
already recorded (bus-position naming on multi-homed machines).

And a test that proved nothing: I asserted `sha256:tooshort` is rejected, but
its letters fall outside a-f, so it failed the character class rather than the
length check. Replaced with hex of the wrong length, after which removing the
length check bites.

src/lifecycle/base.ts

@@ -54,6 +54,19 @@ export async function buildBaseImage(
 
     log("  installing a container runtime");
     await incus(["exec", BUILDER, "--", "pacman", "-Sy", "--noconfirm", "docker"], 600_000);
+
+    // Trust the documentation ranges as plain-HTTP registries.
+    //
+    // A scenario's registry is scenery inside the scenario, serving over HTTP, and a runtime
+    // will not pull from one without being told. Scoped to RFC 5737 and RFC 3849 ranges rather
+    // than a specific address, because those never route on the real internet — so this cannot
+    // make a real machine trust a real registry, whatever it is copied onto.
+    await incus([
+      "exec", BUILDER, "--", "sh", "-c",
+      `mkdir -p /etc/docker && printf '%s' '${JSON.stringify({
+        "insecure-registries": ["192.0.2.0/24", "198.51.100.0/24", "203.0.113.0/24"],
+      })}' > /etc/docker/daemon.json`,
+    ], 60_000);
     await incus(["exec", BUILDER, "--", "systemctl", "enable", "docker"], 60_000);
     await incus(["exec", BUILDER, "--", "systemctl", "start", "docker"], 120_000);