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/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)
+}