fixes crash

src/activities/dictionary/DictionaryMenuActivity.cpp

@@ -39,12 +39,14 @@ void DictionaryMenuActivity::onEnter() {
 void DictionaryMenuActivity::onExit() {
   Activity::onExit();
 
-  // Wait until not rendering to delete task
+  // Take mutex to ensure task isn't in render()
   xSemaphoreTake(renderingMutex, portMAX_DELAY);
   if (displayTaskHandle) {
+    // Task is definitely not in render() because we hold the mutex.
+    // Delete the task - it will never run again.
     vTaskDelete(displayTaskHandle);
     displayTaskHandle = nullptr;
-    vTaskDelay(10 / portTICK_PERIOD_MS);  // Let idle task free stack
+    vTaskDelay(10 / portTICK_PERIOD_MS);  // Let idle task free the task's stack
   }
   vSemaphoreDelete(renderingMutex);
   renderingMutex = nullptr;
@@ -56,7 +58,10 @@ void DictionaryMenuActivity::loop() {
   // Handle back button - cancel
   // Use wasReleased to consume the full button event
   if (mappedInput.wasReleased(MappedInputManager::Button::Back)) {
-    onCancel();
+    // Copy callback before invoking - the callback may destroy this object
+    // (and thus the original std::function) while still executing
+    auto callback = onCancel;
+    callback();
     return;
   }
 
@@ -64,7 +69,9 @@ void DictionaryMenuActivity::loop() {
   // Use wasReleased to consume the full button event
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
     const DictionaryMode mode = (selectedIndex == 0) ? DictionaryMode::SELECT_FROM_SCREEN : DictionaryMode::ENTER_WORD;
-    onModeSelected(mode);
+    // Copy callback before invoking - the callback may destroy this object
+    auto callback = onModeSelected;
+    callback(mode);
     return;
   }