Compose a node's placed data items from the bus and move the readings layout into the sdk, so disk-load measures without a composed file and restic, mounts, nfs-server and the self-check read one layout (issue 1955, ADR 0571 clause 3)

go/compose/frombus/frombus.go

@@ -853,3 +853,13 @@ func membershipOf(own delivery.Composed) string {
 	}
 	return ""
 }
+
+// DataItems is every data item the modules placed on scope's node declare, placed there, composed from the bus as Plans
+// composes (novox/hq ADR 0571 clause 3): disk-load measures these.
+func DataItems(ctx context.Context, r Reader, mesh Mesh, s Scope) (map[string][]catalogue.PlacedDataItem, []string, error) {
+	in, err := Input(ctx, r, mesh, s)
+	if err != nil {
+		return nil, nil, err
+	}
+	return compose.DataItems(in, s.Node)
+}

go/compose/frombus/frombus_test.go

@@ -712,6 +712,18 @@ func TestInput(t *testing.T) {
 		wj, _ := json.MarshalIndent(controllers, "", " ")
 		t.Errorf("the seat's plans differ from the controller's:\n got %s\nwant %s", gj, wj)
 	}
+	// ADR 0571 clause 3: the data items of n1's modules, placed, from the bus alone: what disk-load measures.
+	items, unplaced, err := DataItems(ctx, noSecrets, Mesh{}, Scope{Node: "n1"})
+	if err != nil || len(unplaced) > 0 || len(items) == 0 {
+		t.Errorf("the data items from the bus are %v, unplaced %v: %v", items, unplaced, err)
+	}
+	for module, its := range items {
+		for _, it := range its {
+			if it.Module != module || !strings.HasPrefix(it.Path, "/") || it.Measure == "" {
+				t.Errorf("%s's item %+v is not placed", module, it)
+			}
+		}
+	}
 
 	// And what a provider on another node serves from its settings (mailu's smtp domain, issue 1126: shanks refused
 	// '${setting:domain} ... nothing sets "domain"'): read for that provider's served keys alone, through Served.

go/compose/node.go

@@ -333,3 +333,19 @@ func namedModules(plan catalogue.Resolution, leftOut map[string]string) []string
 	sort.Strings(out)
 	return out
 }
+
+// DataItems is every data item the modules placed on a node declare, placed there (novox/hq ADR 0571 clause 3): what the
+// node-backup holder is handed as `${backup:data}`, composed over the Input as Compose composes the node, so disk-load
+// reads the list from the bus with no composed file. Unplaced names each item left out and why.
+func DataItems(in Input, node string) (map[string][]catalogue.PlacedDataItem, []string, error) {
+	c := newComposer(in)
+	resolved, err := c.planFor(node)
+	if err != nil {
+		return nil, nil, err
+	}
+	rendered, err := c.render(node, Planning)
+	if err != nil {
+		return nil, nil, err
+	}
+	return resolved.Plan.DataItems(rendered.Rendering)
+}