They push and answer each reference, so a key they write themselves can never
carry their own delivery; until R4g build-agent delivers them as it does the
builder.
R4e's own delivery plan waited for ever in tier 1: the controller took every
module but build-agent's own from a referenced builder key, and only R4e's
builder and build modules, delivered by that same plan, write references.
The builder now says so in its bucket of instances; until it does, a walk asks
build-agent as before R4e, and an open walk waiting on a key the running
builder cannot reference is judged again at the next look.
ADR 0520 narrowed after its review: mesh-tools-go builds from its own
directory on a pinned base and has its key from mesh-build-image, and
mesh-tools-python is no module, so the set is named, not derived from
the toolchain bases.
The builder writes no key of build-agent or of the toolchain bases its
builds stand on, so a walk moving one would hold its tier for ever.
Until R4g they are build-agent's own, as the builder's module is; the
bases are read from the toolchains, not copied.
jschoubben