[client] Android back handling

client/lib/ui/app/app_layout.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_state_notifier/flutter_state_notifier.dart';
 import 'package:phylum/ui/app/app_actions.dart';
 import 'package:phylum/ui/app/nav_list.dart';
+import 'package:phylum/ui/app/router.dart';
 import 'package:phylum/ui/app/search.dart';
 import 'package:phylum/ui/explorer/explorer_view.dart';
 import 'package:phylum/ui/explorer/explorer_controller.dart';
@@ -23,6 +24,19 @@ class AppLayout extends StatelessWidget {
         ),
         ChangeNotifierProvider(create: (context) => PhylumSearchController(context)),
       ],
+      builder: (context, child) {
+        final canHandlePop =
+            context.watch<PhylumRouterDelegate>().canGoBack || context.watch<ExplorerState>().selectedIds.isNotEmpty;
+        return PopScope(
+            canPop: !canHandlePop,
+            onPopInvokedWithResult: (didPop, result) {
+              if (didPop) return;
+              if (!context.read<ExplorerController>().clearSelection()) {
+                context.read<PhylumRouterDelegate>().goBack();
+              }
+            },
+            child: child!);
+      },
       child: const AppLayout._(),
     );
   }

client/lib/ui/app/router.dart

@@ -18,6 +18,8 @@ class PhylumRouterDelegate extends RouterDelegate<ExplorerPage> with ChangeNotif
 
   PhylumRouterDelegate({ExplorerPage? page}) : _current = page;
 
+  bool get canGoBack => _back.isNotEmpty;
+
   void go(ExplorerPage page) {
     if (_current != page) {
       _back = [..._back, _current!];

client/lib/ui/explorer/explorer_controller.dart

@@ -135,6 +135,17 @@ class ExplorerController extends StateNotifier<ExplorerState> {
     state = state.copyWith(dragging: dragging);
   }
 
+  bool clearSelection() {
+    if (state.selectedIds.isEmpty) return false;
+    state = state.copyWith(
+      selectedIds: const {},
+      selectionStartIndex: state.selectionStartIndex,
+      focusIndex: state.focusIndex,
+      showFocus: false,
+    );
+    return true;
+  }
+
   void updateSelection(int Function(int)? indexFn, SelectionMode mode, bool highlight) {
     Set<String>? selectedIds;
     int index = indexFn?.call(state.focusIndex) ?? state.focusIndex;