fix(ux): navigate back after deleting all search results (#85)

When the user searches in a mailbox, selects all results, and deletes
them, re-evaluate the search. If no results remain and there is a
previous screen in the navigation stack, pop back to it instead of
clearing the search and showing the regular inbox.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/ui/screens/email_list_screen.dart

@@ -503,7 +503,11 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
           .searchEmails(widget.accountId, widget.mailboxPath, searchQuery);
       if (!mounted) return;
       if (remaining.isEmpty) {
-        _searchController.clear();
+        if (context.canPop()) {
+          context.pop();
+        } else {
+          _searchController.clear();
+        }
       } else {
         setState(() => _searchResults = remaining);
       }

test/widget/email_list_screen_test.dart

@@ -3,9 +3,30 @@ import 'package:flutter_test/flutter_test.dart';
 
 import 'package:sharedinbox/core/models/email.dart';
 import 'package:sharedinbox/di.dart';
+import 'package:sharedinbox/ui/screens/email_list_screen.dart';
+import 'package:sharedinbox/ui/screens/mailbox_list_screen.dart';
 
 import 'helpers.dart';
 
+// A fake email repository whose search results can be changed mid-test.
+class _MutableFakeEmailRepository extends FakeEmailRepository {
+  List<Email> _results;
+
+  _MutableFakeEmailRepository(List<Email> initial)
+      : _results = List.of(initial),
+        super();
+
+  void setSearchResults(List<Email> results) => _results = results;
+
+  @override
+  Future<List<Email>> searchEmails(
+    String accountId,
+    String mailboxPath,
+    String query,
+  ) async =>
+      _results;
+}
+
 final _kDate = DateTime(2024, 6);
 
 void main() {
@@ -405,6 +426,66 @@ void main() {
       expect(find.text('Result email'), findsWidgets);
     });
 
+    testWidgets(
+      'deleting all search results pops back to previous screen',
+      (tester) async {
+        final email = testEmail(subject: 'Needle');
+        final repo = _MutableFakeEmailRepository([email]);
+
+        // Start at the mailbox list so the email list is pushed on top of it,
+        // making context.canPop() == true inside EmailListScreen.
+        await tester.pumpWidget(
+          buildApp(
+            initialLocation: '/accounts/acc-1/mailboxes',
+            overrides: [
+              accountRepositoryProvider.overrideWithValue(
+                FakeAccountRepository([kTestAccount]),
+              ),
+              mailboxRepositoryProvider.overrideWithValue(
+                FakeMailboxRepository([kTestMailbox]),
+              ),
+              emailRepositoryProvider.overrideWithValue(repo),
+            ],
+          ),
+        );
+        await tester.pumpAndSettle();
+
+        expect(find.byType(MailboxListScreen), findsOneWidget);
+
+        // Navigate into INBOX (pushes EmailListScreen onto the stack).
+        await tester.tap(find.text('INBOX'));
+        await tester.pumpAndSettle();
+
+        expect(find.byType(EmailListScreen), findsOneWidget);
+
+        // Search for the email.
+        await tester.enterText(find.byType(TextField), 'Needle');
+        await tester.testTextInput.receiveAction(TextInputAction.search);
+        await tester.pumpAndSettle();
+
+        // 'Needle' also appears in the SearchBar input, so match at least one.
+        expect(find.text('Needle'), findsAtLeastNWidgets(1));
+
+        // Long-press the sender name (unique to the email tile) to enter
+        // selection mode.
+        await tester.longPress(find.text('Bob'));
+        await tester.pumpAndSettle();
+
+        await tester.tap(find.byIcon(Icons.select_all));
+        await tester.pumpAndSettle();
+
+        // After deletion the search re-runs and finds nothing.
+        repo.setSearchResults([]);
+
+        await tester.tap(find.byIcon(Icons.delete));
+        await tester.pumpAndSettle();
+
+        // Should have popped back to the mailbox list.
+        expect(find.byType(EmailListScreen), findsNothing);
+        expect(find.byType(MailboxListScreen), findsOneWidget);
+      },
+    );
+
     testWidgets('shows preview snippet when email has preview', (tester) async {
       final email = Email(
         id: 'acc-1:99',