Fix picker access and finish Wolfskin on root Back

app/src/main/java/com/github/damontecres/wholphin/services/NavigationManager.kt

@@ -2,6 +2,8 @@ package com.github.damontecres.wholphin.services
 
 import androidx.navigation3.runtime.NavBackStack
 import com.github.damontecres.wholphin.ui.nav.Destination
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.receiveAsFlow
 import org.acra.ACRA
 import timber.log.Timber
 import javax.inject.Inject
@@ -15,6 +17,11 @@ class NavigationManager
     @Inject
     constructor() {
         var backStack: MutableList<Destination> = NavBackStack(Destination.Home())
+        private val exits = Channel<Unit>(Channel.CONFLATED)
+        val exitRequests = exits.receiveAsFlow()
+
+        /** Finish the containing task; never expose an older setup/user entry. */
+        fun requestExit() { exits.trySend(Unit) }
 
         /**
          * Go to the specified [com.github.damontecres.wholphin.ui.nav.Destination]
@@ -41,12 +48,14 @@ class NavigationManager
         }
 
         /**
-         * Go to the previous page
+         * Go to the previous page, or exit when there is no parent.
          */
         fun goBack() {
             synchronized(this) {
                 if (backStack.size > 1) {
                     backStack.removeLastOrNull()
+                } else {
+                    requestExit()
                 }
             }
             log()