Ask a node's engine which of its directories the walk would refuse, read-only (issue 358)

Before the node-engine gives a mesh directory its mode and owner only through
a walk that follows no link another account could make, the operator is to
see which directories that walk would refuse on every node, the control-node
included, where no tool reads a path. `node judge-directories <node>` signs
the ask as a hand-over is, under its own context, and prints the engine's
one line per directory; it changes nothing, so it is a seat verb an agent may
call. The node is granted the subject, the controller alone its publish.

cmd/mesh-controller/handover_test.go

@@ -167,3 +167,54 @@ func TestASetuidSearchAsksOnlyAKnownNodeAndFailsOnARefusal(t *testing.T) {
 		t.Fatalf("a start: %v, printed %q", err, out.String())
 	}
 }
+
+// The directory judgement's line asks only a known node, one name and nothing else, fails on a refusal, and says it
+// changed nothing (novox/hq issue 358).
+func TestADirectoryJudgementAsksOnlyAKnownNodeAndSaysItIsReadOnly(t *testing.T) {
+	t.Setenv(link.CallerVar, "jo through mesh-cli on anchor")
+	asked := 0
+	ask := func(answer link.HandOverAnswer) func(node, by string) (link.HandOverAnswer, error) {
+		return func(node, by string) (link.HandOverAnswer, error) {
+			asked++
+			if node != "novox" || by != "jo through mesh-cli on anchor" {
+				t.Fatalf("asked %q %q", node, by)
+			}
+			return answer, nil
+		}
+	}
+	known := func(string) error { return nil }
+	var out bytes.Buffer
+	for _, args := range [][]string{nil, {"novox", "extra"}, {"-x"}} {
+		if err := judgeDirectoriesAsked(args, known, ask(link.HandOverAnswer{Said: "x"}), &out); err == nil || asked != 0 {
+			t.Fatalf("%v was asked: %v", args, err)
+		}
+	}
+	if err := judgeDirectoriesAsked([]string{"novox"}, func(string) error { return errors.New("no node called novox") },
+		ask(link.HandOverAnswer{Said: "x"}), &out); err == nil || asked != 0 {
+		t.Fatalf("an unknown node: %v", err)
+	}
+	if err := judgeDirectoriesAsked([]string{"novox"}, known, ask(link.HandOverAnswer{Refused: "no; nothing was judged"}),
+		&out); err == nil || !strings.Contains(err.Error(), "novox refused") || out.Len() != 0 {
+		t.Fatalf("a refusal: %v, printed %q", err, out.String())
+	}
+	said := "2 directories declared: 1 placed, 1 would be refused\n/var/lib/a: placed\n/var/lib/b: would be refused: …"
+	if err := judgeDirectoriesAsked([]string{"novox"}, known, ask(link.HandOverAnswer{Said: said}), &out); err != nil ||
+		out.String() != "novox (read-only: nothing on novox was changed)\n"+said+"\n" {
+		t.Fatalf("a judgement: %v, printed %q", err, out.String())
+	}
+}
+
+// The judgement is a seat verb an agent may call — it reads, and changes nothing on the node — and runs exactly
+// `node judge-directories <node>` (novox/hq issue 358).
+func TestTheDirectoryJudgementIsAVerbThatOnlyReads(t *testing.T) {
+	argv, err := argvFor("judge-directories", map[string]any{"node": "novox"})
+	if err != nil || strings.Join(argv, " ") != "node judge-directories novox" {
+		t.Fatalf("the verb runs %v, %v", argv, err)
+	}
+	if _, err := argvFor("judge-directories", map[string]any{}); err == nil {
+		t.Fatal("the verb ran with no node")
+	}
+	if !readingVerbs["judge-directories"] {
+		t.Fatal("the judgement is not counted a reading verb")
+	}
+}