Leave out a module whose stored manifest has an unknown field, and raise it (hq ADR 0262 review)

A key dropped silently ran a module without what its manifest says, and a key inside a block still
failed the whole catalogue. Judge a key by what it is about, and narrow the listing to one machine.

cmd/mesh-controller/modules.go

@@ -547,6 +547,12 @@ func settingsCommand(ctx context.Context, args []string) error {
 		if len(positionals) == 1 {
 			only = positionals[0]
 		}
+		if *node != "" {
+			// A machine the mesh does not know is refused, never answered with an empty listing.
+			if _, err := inv.NodeByName(ctx, *node); err != nil {
+				return err
+			}
+		}
 		entries, err := inv.Catalogued(ctx)
 		if err != nil {
 			return err
@@ -557,6 +563,10 @@ func settingsCommand(ctx context.Context, args []string) error {
 			if len(m.Settings) == 0 || (only != "" && m.Module != only) {
 				continue
 			}
+			if *node != "" && !containsString(e.On, *node) {
+				// Asked for one machine: a module not on it has no value there to say.
+				continue
+			}
 			p := preferencesOf{Manifest: m, On: map[string][]catalogue.SettingSource{}}
 			for _, n := range e.On {
 				if *node != "" && n != *node {
@@ -572,7 +582,11 @@ func settingsCommand(ctx context.Context, args []string) error {
 			listed = append(listed, p)
 		}
 		if only != "" && len(listed) == 0 {
-			fmt.Printf("%s declares no preferences\n", only)
+			fmt.Printf("%s declares no preferences%s\n", only, onNode(*node))
+			return nil
+		}
+		if len(listed) == 0 && *node != "" {
+			fmt.Printf("no module on %s declares a preference\n", *node)
 			return nil
 		}
 		fmt.Print(describePreferences(listed))
@@ -610,6 +624,14 @@ func describeEffective(module, where string, values []catalogue.SettingSource) s
 	return b.String()
 }
 
+// onNode is ` on <node>` for one machine, nothing for the whole mesh.
+func onNode(node string) string {
+	if node == "" {
+		return ""
+	}
+	return " on " + node
+}
+
 // preferencesOf is one module's preferences and its value on each machine it is assigned to.
 type preferencesOf struct {
 	Manifest catalogue.Manifest