node-tools: only a call pattern names a caller, and a fall-back for want of a responder is said (hq issue 365, review)

callerOn reads a caller only under the call kind, so a tool subscription ending
in a wildcard never yields one. A caller-named call that reached nobody is said
once per subject before it is asked on the old subject, so a runtime or grant
that drifted behind is seen rather than a quiet unproven. The caller tests wait
for their bundle's exit, which reads the launcher's restart pauses another test
sets.

node-tools/internal/bus/caller_bus_test.go

@@ -180,3 +180,39 @@ func TestAGrantedCallerIsHeardAsItselfAndCannotNameAnother(t *testing.T) {
 		t.Errorf("heard %v; want the asker alone, as itself", got)
 	}
 }
+
+// A fall-back for want of a responder on the caller-named subject is said, once per subject, so a runtime or
+// grant that drifted behind is seen rather than read as a quiet "unproven".
+func TestAFallBackForWantOfAResponderIsSaidOncePerSubject(t *testing.T) {
+	url := mt.URL(t)
+	// A runtime from before issue 365: the subject that names no caller, alone.
+	older, err := nats.Connect(url)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer older.Close()
+	if _, err := older.Subscribe("mesh.mod.ledger.tool.who", func(m *nats.Msg) { _ = m.Respond([]byte(`{"result":{}}`)) }); err != nil {
+		t.Fatal(err)
+	}
+	_ = older.Flush()
+	asker := dial(t, url, "node-tools", "shanks", "shanks.node-tools")
+	var mu sync.Mutex
+	var said []string
+	asker.Logf = func(f string, a ...any) { mu.Lock(); said = append(said, fmt.Sprintf(f, a...)); mu.Unlock() }
+	for i := 0; i < 3; i++ {
+		if _, err := asker.Ask("ledger.who", map[string]any{}, ""); err != nil {
+			t.Fatal(err)
+		}
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	n := 0
+	for _, s := range said {
+		if strings.Contains(s, "nothing answers the caller-named mesh.mod.ledger.call.who.shanks~node-tools") {
+			n++
+		}
+	}
+	if n != 1 {
+		t.Errorf("the fall-back was said %d times, want once: %v", n, said)
+	}
+}