Let root-free take its machines as a list, as the router names them

The router's contract names the machines as a JSON array. A verb's argument declared a list now takes
an array of names (or one text separated by commas), and refuses anything else in it.

internal/catalogue/verbs.go

@@ -435,9 +435,9 @@ var ControllerVerbs = []Verb{
 		"last 15 minutes, and the login shell's execute is not served there. Anything else, a read that failed " +
 		"included, is not free and says why. The router asks it before an answer from a channel proving its sender " +
 		"may approve. Only reads.",
-		Input: schema(map[string]string{
-			"machines": "the machines to judge, separated by commas",
-		}, []string{"machines"})},
+		Input: listed(schema(map[string]string{
+			"machines": "the machines to judge, by name: a list, or one text separated by commas",
+		}, []string{"machines"}), "machines")},
 	{Name: "dead-letters", Description: "Every message a consumer on the bus gave up on after handing it over " +
 		"as often as it may, kept in DEAD_LETTERS: whose consumer, the subject, how often it was handed over and " +
 		"when it was given up, newest first. With id: that one whole, with what it said. With deliver: hand it " +
@@ -554,6 +554,21 @@ func schema(properties map[string]string, required []string, switches ...string)
 	return out
 }
 
+// listed makes the named properties of a schema lists of text: a caller gives them as a JSON array (or, as
+// any argument, one text separated by commas).
+func listed(in map[string]any, names ...string) map[string]any {
+	props, _ := in["properties"].(map[string]any)
+	for _, n := range names {
+		p, _ := props[n].(map[string]any)
+		if p == nil {
+			panic("a list that is not a property: " + n)
+		}
+		props[n] = map[string]any{"type": "array", "items": map[string]any{"type": "string"},
+			"description": p["description"]}
+	}
+	return in
+}
+
 // unpromised is what a claim says it serves and the seat's protocol never promised.
 func unpromised(serves []string, promised []Verb) []string {
 	has := map[string]bool{}