The controller's tools can set an assignment's settings

Per-machine and mesh-wide settings could be set only from the
controller's command line. The settings verb runs settings set|clear,
passing the values inline, which the command now accepts as well as a
file (novox/hq issue 198).

cmd/mesh-controller/modules.go

@@ -352,10 +352,14 @@ func settingsCommand(ctx context.Context, args []string) error {
 	switch args[0] {
 	case "set":
 		if len(positionals) != 2 {
-			return errors.New("settings set <module> <settings.json> [--node <node>]")
+			return errors.New("settings set <module> <settings.json | {…}> [--node <node>]")
 		}
-		raw, err := os.ReadFile(positionals[1])
-		if err != nil {
+		// A file, or the values themselves when they begin with `{` — which is how the mesh's own
+		// `settings` tool passes them, having no file to hand over (novox/hq issue 198).
+		var raw []byte
+		if strings.HasPrefix(strings.TrimSpace(positionals[1]), "{") {
+			raw = []byte(positionals[1])
+		} else if raw, err = os.ReadFile(positionals[1]); err != nil {
 			return err
 		}
 		var values map[string]any

cmd/mesh-controller/seatverbs.go

@@ -129,6 +129,25 @@ func argvFor(verb string, args map[string]any) ([]string, error) {
 		// Half of either shape: the command says its usage, which names both shapes, and that is
 		// the answer the caller needs.
 		return []string{"rotate"}, nil
+	case "settings":
+		// `settings set|clear` at a shell (novox/hq issue 198). The values travel as an argument
+		// because a tool has no file to hand the command; the command reads either.
+		if err := need("module"); err != nil {
+			return nil, err
+		}
+		argv := []string{"settings", "set", str("module")}
+		switch {
+		case str("clear") == "true":
+			argv = []string{"settings", "clear", str("module")}
+		case str("values") != "":
+			argv = append(argv, str("values"))
+		}
+		// Neither values nor clear: the command says its usage, which names both, and that is the
+		// answer the caller needs — the same as `rotate` given half of either shape.
+		if n := str("node"); n != "" {
+			argv = append(argv, "--node", n)
+		}
+		return argv, nil
 	case "issue":
 		// The same act as `module issue` at a shell (novox/hq design 25 §4): the account is minted
 		// into the mesh's records and delivered at the machine's next push, which is the caller's to

cmd/mesh-controller/seatverbs_test.go

@@ -73,6 +73,22 @@ func TestRotateTakesAProvisionOrAnOwnSecret(t *testing.T) {
 	}
 }
 
+// `settings` is `settings set|clear` at a shell, with the values passed inline (novox/hq issue 198).
+func TestSettingsSetsOrClearsALayer(t *testing.T) {
+	argv, err := argvFor("settings", map[string]any{"module": "dnsmasq", "values": `{"a":1}`, "node": "ace"})
+	if err != nil || strings.Join(argv, " ") != `settings set dnsmasq {"a":1} --node ace` {
+		t.Fatalf("set on a machine: %v %v", argv, err)
+	}
+	argv, _ = argvFor("settings", map[string]any{"module": "dnsmasq", "clear": "true"})
+	if strings.Join(argv, " ") != "settings clear dnsmasq" {
+		t.Fatalf("clear for the mesh: %v", argv)
+	}
+	argv, _ = argvFor("settings", map[string]any{"module": "dnsmasq"})
+	if strings.Join(argv, " ") != "settings set dnsmasq" {
+		t.Fatalf("a set with no values falls to the command's usage: %v", argv)
+	}
+}
+
 // `issue` is `module issue` at a shell: the module and the machine, and nothing that would push. A
 // module's bus account was mintable only from the controller's command line, so an agent working
 // through the tools could not finish a rollout that gave a module one (novox/hq issue 191).

internal/catalogue/verbs.go

@@ -136,6 +136,15 @@ var ControllerVerbs = []Verb{
 			"node":   "the machine that runs the module",
 			"module": "the module's name",
 		}, []string{"node", "module"})},
+	{Name: "settings", Description: "Set what an assignment is configured with: a module's settings for the whole mesh, " +
+		"or for one machine. Replaces that layer whole — what it does not name, it no longer sets — and takes effect " +
+		"at the next push. With clear, removes the layer and the module is back to what its definition says.",
+		Input: schema(map[string]string{
+			"module": "the module's name",
+			"values": "the settings as a JSON object, for set",
+			"node":   "one machine; the whole mesh when absent",
+			"clear":  "\"true\" to remove the layer instead of setting it",
+		}, []string{"module"})},
 	{Name: "build", Description: "Have the build machine build a repository. Answers at once with the build's id: " +
 		"`builds` with that id follows it line by line, and the module is registered when the outcome comes.",
 		Input: schema(map[string]string{