[android,ui] chore: back action behavior (a16 hypoeros) fix attempt 1

src/android/app/src/main/java/org/yuzu/yuzu_emu/features/settings/ui/SettingsActivity.kt

@@ -108,9 +108,10 @@ class SettingsActivity : AppCompatActivity() {
     fun navigateBack() {
         val navHostFragment =
             supportFragmentManager.findFragmentById(R.id.fragment_container) as NavHostFragment
-        if (navHostFragment.childFragmentManager.backStackEntryCount > 0) {
-            navHostFragment.navController.popBackStack()
-        } else {
+        val navController = navHostFragment.navController
+        val popped = navController.popBackStack()
+
+        if (!popped) {
             finishWithFragmentLikeAnimation()
         }
     }

src/android/app/src/main/java/org/yuzu/yuzu_emu/fragments/EmulationFragment.kt

@@ -879,7 +879,7 @@ class EmulationFragment : Fragment(), SurfaceHolder.Callback {
         setInsets()
 
         requireActivity().onBackPressedDispatcher.addCallback(
-            requireActivity(),
+            viewLifecycleOwner,
             object : OnBackPressedCallback(true) {
                 override fun handleOnBackPressed() {
                     if (!NativeLibrary.isRunning()) {

src/android/app/src/main/java/org/yuzu/yuzu_emu/ui/main/MainActivity.kt

@@ -12,6 +12,7 @@ import android.view.ViewGroup.MarginLayoutParams
 import android.view.WindowManager
 import android.view.animation.PathInterpolator
 import android.widget.Toast
+import androidx.activity.OnBackPressedCallback
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.activity.viewModels
 import androidx.appcompat.app.AppCompatActivity
@@ -153,6 +154,7 @@ class MainActivity : AppCompatActivity(), ThemeProvider {
         val navHostFragment =
             supportFragmentManager.findFragmentById(R.id.fragment_container) as NavHostFragment
         setUpNavigation(navHostFragment.navController)
+        installBackPressPolicy(navHostFragment.navController)
 
         homeViewModel.statusBarShadeVisible.collect(this) { showStatusBarShade(it) }
         homeViewModel.contentToInstall.collect(
@@ -330,6 +332,28 @@ class MainActivity : AppCompatActivity(), ThemeProvider {
         }
     }
 
+    private fun installBackPressPolicy(navController: NavController) {
+        onBackPressedDispatcher.addCallback(
+            this,
+            object : OnBackPressedCallback(true) {
+                override fun handleOnBackPressed() {
+                    val isOnGamesScreen = navController.currentDestination?.id == R.id.gamesFragment
+                    if (isOnGamesScreen) {
+                        // Allow native OS/app exit behavior only from the games root screen.
+                        isEnabled = false
+                        onBackPressedDispatcher.onBackPressed()
+                        isEnabled = true
+                        return
+                    }
+
+                    if (!navController.popBackStack()) {
+                        navController.navigate(R.id.gamesFragment)
+                    }
+                }
+            }
+        )
+    }
+
     private fun showStatusBarShade(visible: Boolean) {
         binding.statusBarShade.animate().apply {
             if (visible) {