fix(wireplumber): guard async load callbacks against use-after-free on teardown

The WirePlumber module registers three async callbacks (onDefaultNodesApiLoaded,
onMixerApiLoaded, onPluginActivated) that receive a raw self pointer with a NULL
GCancellable. WirePlumber cannot withdraw an in-flight callback, so if the module
is destroyed before a queued callback fires (e.g. a temporary output/bar is removed
while a component load is still pending, or during an audio route transition), the
callback dereferences the freed self, causing heap corruption / a crash.

Guard each of these callbacks with isModuleAlive(), which checks the existing static
modules registry. The destructor already removes this from the registry before any
teardown, so a missing entry means self is dangling and the callback bails out
without touching it.

A GCancellable cannot fix this cleanly here: every callback dereferences self on its
first line, and wp_core_load_component completes via a WpTransition (not a GTask), so
the cancellable is not recoverable from the GAsyncResult either. The liveness check
must not touch self at all.

Fixes #3974.

include/modules/wireplumber.hpp

@@ -36,6 +36,9 @@ class Wireplumber : public ALabel {
   std::vector<std::string> getWPIcon();
 
   static std::list<waybar::modules::Wireplumber*> modules;
+  // Returns true while `self` is still a live module. Async load/activation callbacks use this to
+  // avoid dereferencing a `self` that was destroyed before the callback fired (see #3974).
+  static bool isModuleAlive(waybar::modules::Wireplumber* self);
 
   uint32_t resolvePhysicalSink(uint32_t start_id);
   uint32_t findPlaybackNodeId(const gchar* description);

src/modules/wireplumber.cpp

@@ -10,6 +10,17 @@ bool isValidNodeId(uint32_t id) { return id > 0 && id < G_MAXUINT32; }
 
 std::list<waybar::modules::Wireplumber*> waybar::modules::Wireplumber::modules;
 
+// Async load/activation callbacks (onDefaultNodesApiLoaded, onMixerApiLoaded, onPluginActivated)
+// are handed a raw `self` pointer with no GCancellable, and WirePlumber has no way to withdraw an
+// in-flight callback. If the module is destroyed before such a callback fires (e.g. an output/bar
+// is removed while a component load is still pending, or during an audio route transition), the
+// callback would dereference a freed `self`. The destructor removes `this` from this registry
+// before any teardown, so a missing entry means `self` is dangling and the callback must bail out
+// without touching it. See https://github.com/Alexays/Waybar/issues/3974.
+bool waybar::modules::Wireplumber::isModuleAlive(waybar::modules::Wireplumber* self) {
+  return std::find(modules.begin(), modules.end(), self) != modules.end();
+}
+
 waybar::modules::Wireplumber::Wireplumber(const std::string& id, const Json::Value& config)
     : ALabel(config, "wireplumber", id, "{volume}%"),
       wp_core_(nullptr),
@@ -387,6 +398,10 @@ void waybar::modules::Wireplumber::onObjectManagerInstalled(waybar::modules::Wir
 
 void waybar::modules::Wireplumber::onPluginActivated(WpObject* p, GAsyncResult* res,
                                                      waybar::modules::Wireplumber* self) {
+  if (!isModuleAlive(self)) {
+    return;
+  }
+
   const auto* pluginName = wp_plugin_get_name(WP_PLUGIN(p));
   spdlog::debug("[{}]: onPluginActivated: {}", self->name_, pluginName);
   g_autoptr(GError) error = nullptr;
@@ -432,6 +447,10 @@ void waybar::modules::Wireplumber::prepare(waybar::modules::Wireplumber* self) {
 
 void waybar::modules::Wireplumber::onDefaultNodesApiLoaded(WpObject* p, GAsyncResult* res,
                                                            waybar::modules::Wireplumber* self) {
+  if (!isModuleAlive(self)) {
+    return;
+  }
+
   gboolean success = FALSE;
   g_autoptr(GError) error = nullptr;
 
@@ -453,6 +472,10 @@ void waybar::modules::Wireplumber::onDefaultNodesApiLoaded(WpObject* p, GAsyncRe
 
 void waybar::modules::Wireplumber::onMixerApiLoaded(WpObject* p, GAsyncResult* res,
                                                     waybar::modules::Wireplumber* self) {
+  if (!isModuleAlive(self)) {
+    return;
+  }
+
   gboolean success = FALSE;
   g_autoptr(GError) error = nullptr;