Say what a build was made from, and hand an image compiling Go only that (hq ADR 0267, issue 363)

A merge to the controller's repository moved the route proxy and the build
seat's holder whatever it changed, because nothing said which files their
builds read. A build of a trunk commit now says its build source per
repository: a Go program's import closure, an archive's directory, an
image's recipe and the package it names in the new 'compiles' field. That
image is built from its build source alone, so a recipe reading past it
fails by name, and its fingerprint is over what it was handed.

cmd/mesh-builder/main.go

@@ -306,6 +306,9 @@ func answer(ctx context.Context, publisher builder.Publisher, on, workspace stri
 			for _, r := range built.Read {
 				result.Read = append(result.Read, link.ReadRepository{Repository: r.Repository, Ref: r.Ref})
 			}
+			for _, s := range built.Sources {
+				result.Sources = append(result.Sources, link.BuildSource{Repository: s.Repository, Ref: s.Ref, Paths: s.Paths})
+			}
 			say("built", built.Manifest.Module+" from "+short(built.Commit))
 		}
 	}