disable the NavHost back handling and drive back ourselves

Keeps the NavHost composed (the dropped-NavHost version left the still-transparent
overlay over black) while stopping the controller from winning the back over the
overlay's BackHandler. Back now: queue -> now playing -> pop the route.

app/src/main/kotlin/com/subtracks/ui/AppRoot.kt

@@ -183,15 +183,11 @@ private fun MainNavigation() {
     ArtworkTheme(artwork) {
         Box(Modifier.fillMaxSize()) {
             Column(Modifier.fillMaxSize().imePadding()) {
-                Box(Modifier.weight(1f)) {
-                    // The now playing overlay covers this, and while it is up we drop the NavHost so
-                    // it cannot steal the back from the overlay's BackHandler.
-                    if (!nowPlayingOpen) {
                 NavHost(
                     navController = navController,
                     modifier =
                         Modifier
-                                    .fillMaxSize()
+                            .weight(1f)
                             .then(
                                 if (playerVisible) {
                                     Modifier.consumeWindowInsets(WindowInsets.navigationBars)
@@ -291,8 +287,6 @@ private fun MainNavigation() {
                         )
                     }
                 }
-                    }
-                }
 
                 AnimatedVisibility(
                     visible = showMiniPlayer,
@@ -377,8 +371,15 @@ private fun MainNavigation() {
         }
     }
 
-    BackHandler(enabled = showingQueue) { showingQueue = false }
+    // The NavHost registers its own back callback, and OnBackPressedDispatcher hands the back to
-    BackHandler(enabled = nowPlayingOpen && !showingQueue) {
+    // the last-registered enabled callback, so it can win over the overlay's BackHandler and pop
-        settleNowPlaying(false)
+    // the route underneath. Disable the controller's back and drive navigation ourselves.
+    LaunchedEffect(navController) { navController.enableOnBackPressed(false) }
+    BackHandler(enabled = showingQueue || nowPlayingOpen || navController.previousBackStackEntry != null) {
+        when {
+            showingQueue -> showingQueue = false
+            nowPlayingOpen -> settleNowPlaying(false)
+            else -> navController.popBackStack()
+        }
     }
 }