give: test that a trusted party's secret given at the terminal is announced before it is kept, and refuse an unknown machine before anybody types

The terminal path's order is one function, keepGiven, so the test fails when the announcement before a
trusted party's secret is removed, and when a failed announcement still keeps it. give also refuses a
machine the mesh does not know, as the secret's or as the desk, before the prompt (the final review).

cmd/mesh-controller/desk_secret.go

@@ -39,6 +39,9 @@ const deskPromptWithin = 25
 type deskGive struct {
 	// declares refuses a module or a secret the mesh would refuse, before anybody is asked to type.
 	declares func(module, name string) error
+	// known refuses a machine the mesh does not know, before anybody is asked to type; nil knows every one
+	// (a test that does not look).
+	known func(machine string) error
 	// trusted says a module runs as an account of its own: its secret is never taken at a desk (below). Nil is
 	// never (a test that does not look).
 	trusted func(module string) (bool, error)
@@ -63,6 +66,14 @@ func (d deskGive) give(node, module, name, desk string) (string, error) {
 			return "", fmt.Errorf("%s is not named", what)
 		}
 	}
+	if d.known != nil {
+		for what, machine := range map[string]string{"the machine the secret is for": node, "the desk": desk} {
+			if err := d.known(machine); err != nil {
+				return "", fmt.Errorf("nobody was asked to type anything: %s, %s, is not a machine this mesh knows: %w",
+					what, machine, err)
+			}
+		}
+	}
 	if err := d.declares(module, name); err != nil {
 		return "", fmt.Errorf("nobody was asked to type anything: %w", err)
 	}
@@ -164,7 +175,11 @@ func giveAtDesk(ctx context.Context, node, module, name, desk string) error {
 	defer open.Close()
 	d := deskGive{
 		declares: func(module, name string) error { return open.inventory.DeclaresOwnSecret(ctx, module, name) },
-		trusted:  func(module string) (bool, error) { return open.inventory.RunsAsItsOwnAccount(ctx, module) },
+		known: func(machine string) error {
+			_, err := open.inventory.NodeByName(ctx, machine)
+			return err
+		},
+		trusted: func(module string) (bool, error) { return open.inventory.RunsAsItsOwnAccount(ctx, module) },
 		ask: func(machine string, args map[string]any) (json.RawMessage, error) {
 			var result json.RawMessage
 			err := onTheBus(func(conn *nats.Conn) error {