Sign in again to the hub last signed in to

Co-Authored-By: Claude Opus 5.5 <[email protected]>

internal/control/control_test.go

@@ -109,6 +109,11 @@ func TestSignInAndOut(t *testing.T) {
 	if _, err := os.Stat(path); !os.IsNotExist(err) {
 		t.Fatalf("hub.json: %v", err)
 	}
+	// Signing in again goes to the same hub.
+	m.DefaultHub = "https://elsewhere.test"
+	if s := ask(t, m, "GET", "/hub", ""); s.Hub != srv.URL {
+		t.Fatalf("hub after signing out: %q", s.Hub)
+	}
 
 	// Only https hubs (or this computer's); other requests to the proxy's address are refused.
 	u, _ := url.Parse("http://" + Host + "/hub/signin")