simpler check and deps messages

rig/docs/notes/Dockerfile.deps.md

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+# ctrl/Dockerfile.deps
+
+## Purpose
+
+The toolchain installer image. It does NOT run the cluster — it installs a toolchain onto the host and gets out of the way.
+
+This exists to kill a bootstrap paradox: a plain bash installer needs curl, jq and sha256sum to already be present, and a minimal Debian has none of them. It carries its own toolchain, so the only host prerequisite is Docker.
+
+## Variants
+
+Two variants from one file:
+
+```
+docker build -f ctrl/Dockerfile.deps --target deps      -t <slug>-deps      .
+docker build -f ctrl/Dockerfile.deps --target deps-full -t <slug>-deps:full .
+```
+
+`deps-full` bakes every pinned binary in at build time. `docker save` it and you have the whole installer as one file to carry into an air-gapped network.
+
+## Packages
+
+ca-certificates + curl: fetch and verify. graphviz + python3: render diagrams and validate the arch model, so the host never needs an apt package.
+
+docker-cli, NOT docker.io: we only ever talk to the host's daemon through the mounted socket, and under `--no-install-recommends` the docker.io package ships docker-init without the actual `docker` binary.
+
+## The installer is the standalone kit
+
+The installer is the generated standalone kit, not deps.sh plus the files it reads. A kit is one file with its pins frozen in and is proven to run with nothing else from rig present — which is exactly what an image needs, and `make standalone` keeps it current. Pins are the same in every profile's kit.