protocols/activation: send an invalid token when serial isn't valid (#11505)

src/protocols/XDGActivation.cpp

@@ -1,6 +1,7 @@
 #include "XDGActivation.hpp"
 #include "../managers/TokenManager.hpp"
 #include "../Compositor.hpp"
+#include "../managers/SeatManager.hpp"
 #include "core/Compositor.hpp"
 #include <algorithm>
 
@@ -23,6 +24,12 @@ CXDGActivationToken::CXDGActivationToken(SP<CXdgActivationTokenV1> resource_) :
             return;
         }
 
+        if (!g_pSeatManager->serialValid(g_pSeatManager->seatResourceForClient(m_resource->client()), m_serial)) {
+            LOGM(LOG, "serial not found, sending invalid token");
+            m_resource->sendDone("__invalid__");
+            return;
+        }
+
         m_committed = true;
         // send done with a new token
         m_token = g_pTokenManager->registerNewToken({}, std::chrono::months{12});