Take a module in from the builder's done key of its trunk fingerprint: one record of the key's artifacts, its manifest judged against the catalogue trunk's predefined keys (issue 1851, A3, A4b, A4c)

internal/buildreads/buildreads.go

@@ -0,0 +1,39 @@
+// Package buildreads is which repositories other than a module's own its build reads source from, as its manifest
+// names them (novox/hq 04-ISSUES/131): the artifacts' `context` repositories. One rule for build-agent, which says it
+// in a build's outcome, and for the controller, which reads it from a done key's manifest (R4e, issue 1851): it lives
+// here, not in internal/builder, so it outlasts build-agent (R4g).
+package buildreads
+
+import (
+	"sort"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// Of is every repository other than the module's own that this build's recipes read source from, each once and in a
+// fixed order, so two builds of one commit report the same thing the same way.
+func Of(manifest catalogue.Manifest) []catalogue.ArtifactContext {
+	if manifest.Build == nil {
+		return nil
+	}
+	seen := map[string]bool{}
+	var out []catalogue.ArtifactContext
+	for _, a := range manifest.Build.Artifacts {
+		if a.Context == nil || a.Context.Repository == "" {
+			continue
+		}
+		key := a.Context.Repository + "#" + a.Context.Ref
+		if seen[key] {
+			continue
+		}
+		seen[key] = true
+		out = append(out, *a.Context)
+	}
+	sort.Slice(out, func(i, j int) bool {
+		if out[i].Repository != out[j].Repository {
+			return out[i].Repository < out[j].Repository
+		}
+		return out[i].Ref < out[j].Ref
+	})
+	return out
+}