The control plane's recipe starts FROM the base its manifest declares, and an undeclared base is refused

The mesh's own images declare theirs now, so the refusal ADR 0097 deferred is live.
The builder's own image and the examples take arguments with defaults; make builds
them, not the mesh.

cmd/mesh-builder/Dockerfile

@@ -1,17 +1,19 @@
+ARG ALPINE_BASE=alpine:3
+ARG GO_BASE=golang:1.25-alpine
 # The builder, as a module ships one.
 #
 # Not FROM scratch, unlike the control plane: this one runs git and a container client, so it
 # needs a filesystem with them on it. That is the honest cost of a machine whose job is to build —
 # and it is why building is a MODULE on a machine that has a runtime rather than something the
 # control plane does (novox/hq ADR 0005).
-FROM golang:1.25-alpine AS build
+FROM ${GO_BASE} AS build
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
 COPY . .
 RUN CGO_ENABLED=0 go build -trimpath -ldflags '-s -w' -o /mesh-builder ./cmd/mesh-builder
 
-FROM alpine:3
+FROM ${ALPINE_BASE}
 # git to clone what it is asked to build, and the docker client to build and push it. The daemon
 # is the machine's, reached through its socket — a build machine shares the runtime it was given
 # rather than running one inside itself.