Fill a preference's ${setting:} from its manifest default (hq ADR 0262)

Without a default, a running module could never gain a setting: the file asking for it
failed to compose until set, and the key was refused as stray until a file asked for it.
Defaults sit under the mesh's and the node's settings, never merge into a JSON file, are
refused for the operator's own values, and settings shows each value's source.

internal/catalogue/settings.go

@@ -151,6 +151,12 @@ func settle(base map[string]any, layers []Layer, protected map[string]bool, what
 	map[string]any, error) {
 	merged := deepCopy(base)
 	for _, layer := range layers {
+		if layer.From == DefaultLayer {
+			// A module's own defaults fill ${setting:<key>} only (novox/hq ADR 0262). A mergeable
+			// file's content already is its defaults, and a contribution or served fact declares its
+			// own; laid on here, a default would reach every mergeable file of its module (issue 168).
+			continue
+		}
 		for key, value := range layer.Values {
 			if key == PortsSetting {
 				// Where the machine puts a port is the mesh's to apply, not a value for a file or
@@ -224,6 +230,11 @@ func UnusedSettings(m Manifest, layers []Layer) []string {
 	}
 
 	lands := settingKeysUsedBy(m)
+	// A key the module gives a default reaches what asks for it (novox/hq ADR 0262): setting it
+	// overrides the default, which is how a running module gains a setting without a gap between.
+	for key := range m.Settings {
+		lands[key] = true
+	}
 	for _, values := range m.Contributes {
 		for key := range values {
 			lands[key] = true
@@ -420,7 +431,7 @@ func JudgeSettings(m Manifest, layers []Layer, adopted bool) error {
 		for k, v := range settled {
 			copied[k] = v
 		}
-		if err := settingInto(copied, layers, m.Module); err != nil {
+		if err := settingInto(copied, WithDefaults(m, layers), m.Module); err != nil {
 			return err
 		}
 	}