Bases reach a recipe as build arguments, so the digest was never in the file the builder read
edges from: no build on the mesh recorded what it stood on, and 'build --on', the bases-first
order and the merge follow-up all walked a graph with no edges (novox/hq 04-ISSUES/131). The
builder now reports every base it resolved; the controller records them by artifact path and
reads the newest build's edges from the store, since a recorded manifest carries no build.on.