Fix back behavior after deselecting all items in the gallery.

feature/media-send/src/main/java/org/signal/mediasend/MediaSendFlowEvent.kt

@@ -25,4 +25,5 @@ internal sealed interface MediaSendFlowEvent {
   data class NavigateToFiles(val mediaFolder: MediaFolder) : MediaSendFlowEvent
   data object NavigateToEdit : MediaSendFlowEvent
   data object NavigateToCamera : MediaSendFlowEvent
+  data object NavigateBack : MediaSendFlowEvent
 }

feature/media-send/src/main/java/org/signal/mediasend/MediaSendFlowViewModel.kt

@@ -256,6 +256,25 @@ class MediaSendFlowViewModel(
       is MediaSendFlowEvent.NavigateToFiles -> backStack.goToFiles(event.mediaFolder)
       MediaSendFlowEvent.NavigateToEdit -> backStack.goToEdit()
       MediaSendFlowEvent.NavigateToCamera -> backStack.goToCamera()
+      MediaSendFlowEvent.NavigateBack -> onPopFromSelect()
+    }
+  }
+
+  /**
+   * Backs out of a select screen while nothing is selected, stepping over an editor that would have nothing to edit
+   * and no toolbar to leave by. Decided here rather than when the selection empties, so that re-selecting something
+   * still returns the user to their editor.
+   */
+  private fun onPopFromSelect() {
+    val destination = backStack.dropLast(1).dropLastWhile { it == MediaSendRoute.Edit }
+
+    if (destination.isEmpty()) {
+      sendHudCommand(MediaSendFlowHudCommand.CloseScreen)
+      return
+    }
+
+    while (backStack.size > destination.size) {
+      backStack.pop()
     }
   }
 

feature/media-send/src/main/java/org/signal/mediasend/screens/select/MediaSelectScreen.kt

@@ -5,6 +5,7 @@
 
 package org.signal.mediasend.screens.select
 
+import androidx.activity.compose.BackHandler
 import androidx.activity.compose.LocalOnBackPressedDispatcherOwner
 import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.core.animateDpAsState
@@ -129,6 +130,12 @@ internal fun MediaSelectScreen(
   val gridState = rememberLazyGridState()
   val dragToSelectState = rememberDragToSelectMediaState(state, onEvent, gridState)
 
+  // Only an empty selection can leave an editor with nothing to edit behind us. Every other back press is left to the
+  // navigation default, which keeps its predictive-back gesture.
+  BackHandler(enabled = state.selectedMedia.isEmpty()) {
+    onEvent(MediaSelectScreenEvents.NavigateBack)
+  }
+
   // Once the selection starts refusing items there is nothing left for the drag to do, and letting it run on would
   // raise a refusal for every further tile it crosses.
   LaunchedEffect(state.isSelectionRejected) {

feature/media-send/src/main/java/org/signal/mediasend/screens/select/MediaSelectScreenEvents.kt

@@ -34,6 +34,7 @@ sealed interface MediaSelectScreenEvents {
   data class ReorderSelectedMedia(val fromIndex: Int, val toIndex: Int) : MediaSelectScreenEvents
   data object NavigateToEdit : MediaSelectScreenEvents
   data object NavigateToCamera : MediaSelectScreenEvents
+  data object NavigateBack : MediaSelectScreenEvents
 
   /** Re-read the gallery and the current permission level, e.g. after coming back from app settings. */
   data object Refresh : MediaSelectScreenEvents

feature/media-send/src/main/java/org/signal/mediasend/screens/select/MediaSelectViewModel.kt

@@ -92,6 +92,7 @@ internal class MediaSelectViewModel(
       is MediaSelectScreenEvents.ReorderSelectedMedia -> parentEventEmitter(MediaSendFlowEvent.ReorderSelectedMedia(event.fromIndex, event.toIndex))
       MediaSelectScreenEvents.NavigateToEdit -> parentEventEmitter(MediaSendFlowEvent.NavigateToEdit)
       MediaSelectScreenEvents.NavigateToCamera -> parentEventEmitter(MediaSendFlowEvent.NavigateToCamera)
+      MediaSelectScreenEvents.NavigateBack -> parentEventEmitter(MediaSendFlowEvent.NavigateBack)
       MediaSelectScreenEvents.Refresh -> refresh()
       MediaSelectScreenEvents.RequestMediaPermissions -> requestReadMediaPermissions(reportDenial = true)
       MediaSelectScreenEvents.SelectMorePhotos -> requestReadMediaPermissions(reportDenial = false)