Boot a machine from your mirror
Everyone secures their packages and then installs them on an operating system fetched over the internet on the day the machine was built. That OS is the last dependency, and it is the one most supply chains never account for. It is also the one class LibWorld refuses to take on trust at all: every other artifact is verified when upstream published a claim to check it against, and an image is verified because its source said in advance what the bytes must be.
It learns what the bytes should be
A source declares its checksums file, its detached signature, and a keyring. The manifest's line for a given image becomes the REQUIRED digest — the mirror is told what correct looks like rather than trusting whatever arrives first.
Verification uses gpgv, never gpg --verify. gpgv consults exactly the keyring it is handed: no keyserver, no web of trust. gpg --verify against a default keyring succeeds for any installed key, which is a weaker claim wearing an identical exit code.
It fails closed. A source that declares a signature but has no keyring is refused when the config LOADS, not silently downgraded to checksums-only.
From image to booted machine
Declared images become generated iPXE scripts — a menu, and one entry per image — so a machine with no operating system on it at all can boot from the mirror and install from it. One has: a machine here was rebuilt from bare metal, Ubuntu and all, with every byte coming from the mirror.
Posture is reported per source — signed, checksums-only, or unverified, plus whether the keyring is present — because a fleet can honestly have one of each, and a single global claim would misrepresent two of them.
What it costs
Stated plainly, because a claim with no stated cost is the one nobody re-checks.
Serving a multi-gigabyte image to a slow client is its own problem: nginx's default proxy buffering capped every artifact at 1 GiB for a client slower than the mirror, which presented as a corrupt image rather than as a timeout. Buffering is off on the pull prefixes for exactly that reason.