Wait for a done key whose artifact names no reference, as the controller's take-in does, and hold the fold guard with a row (issue 1126, review round 1)

go/compose/frombus/frombus_test.go

@@ -43,9 +43,11 @@ type bus struct {
 	fetched    []string
 	served     map[string]map[string]any
 	servedRead []string
+	buildsRead []string
 }
 
 func (b *bus) Build(_ context.Context, module, fp string) (*delivery.BuilderBuild, error) {
+	b.buildsRead = append(b.buildsRead, module)
 	return b.builds[module+" "+fp], nil
 }
 
@@ -587,6 +589,26 @@ func TestInput(t *testing.T) {
 	if c := fromBuild[resticKey]; len(c.Filled) != 4 { // its three templated files and its own secret
 		t.Errorf("restic is not handed to the provisioner: its filled files are %v", c.Filled)
 	}
+	// A done key an artifact of which names no reference is waited for, in the controller's words (ADR 0498 §8).
+	unreferenced := movedMesh(true)
+	unreferenced.builds["restic "+movedFps["restic"]].Artifacts = []delivery.BuiltArtifact{{Name: "tools", Kind: "bundle", Digest: digestOf("6")}, resticArtifacts[1]}
+	if _, _, err := Compose(ctx, unreferenced, Mesh{}, Scope{Node: "n1"}, movedFps); err == nil || !strings.Contains(err.Error(), "the build of restic is done and waits for the reference of tools") {
+		t.Errorf("a done key with an unreferenced artifact: %v", err)
+	}
+	// A module the node runs inside its own composition (the fold) composes from the indexer's manifest though a done
+	// build of it is at the trunk's FP2: its build is not read.
+	folding := movedMesh(true)
+	foldIn, err := Input(ctx, folding, Mesh{}, Scope{Node: "n1", InOwn: []string{"mesh-provisioner-client"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	clientParsed, err := catalogue.ParseManifestForInputs(clientRaw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if slices.Contains(folding.buildsRead, "mesh-provisioner-client") || !reflect.DeepEqual(foldIn.Catalogue["mesh-provisioner-client"], clientParsed) {
+		t.Errorf("a folded module was taken from its build: builds read %v", folding.buildsRead)
+	}
 	// The controller's: its take-in resolves each manifest with the key's artifacts and the archive's texts, and composes
 	// from those over the same input.
 	storeIn, err := Input(ctx, movedMesh(false), Mesh{}, Scope{Node: "n1"})