Say a layer whole where the mesh reports it, and give tests their placement (issue 651)

The facts snapshot, the take preview and the settings history read a layer as it
was set; tests that place give the layer through LayerOf.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/catalogue/setting_defaults_test.go

@@ -427,7 +427,7 @@ func TestALeftOutModulesUnplaceableBackupLineCostsOnlyThatLine(t *testing.T) {
 	r := anAdoptedAnchor()
 	r.Modules = append(r.Modules, holder, media, placedBadly)
 	with := anchorRendering(false)
-	with.Settings["notes"] = []Layer{{From: "anchor", Values: map[string]any{PlacesSetting: "not a map"}}}
+	with.Settings["notes"] = []Layer{LayerOf("anchor", map[string]any{PlacesSetting: "not a map"})}
 	composed, err := r.Compose(with)
 	if err != nil {
 		t.Fatalf("an unplaceable line of a left-out module failed the machine: %v", err)