feat(search): match word prefix, not arbitrary substring (#96)

Searching for "foo" now finds "foobar" (prefix of a word) but not
"blafoo" (suffix). The FTS5 query already used the foo* prefix form;
this commit extends the same semantics to folder-name and address
matching in the search screen, replacing contains() with a
word-boundary regex check. Tests added for all three paths.

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

lib/ui/screens/search_screen.dart

@@ -15,6 +15,11 @@ final _searchHistoryProvider =
   return ref.watch(searchHistoryRepositoryProvider).getRecentSearches();
 });
 
+/// Returns true if [text] contains a word that starts with [query].
+/// "foo" matches "foobar" or "My Foobar" but NOT "blafoo".
+bool _hasWordPrefix(String text, String query) =>
+    RegExp(r'\b' + RegExp.escape(query), caseSensitive: false).hasMatch(text);
+
 class SearchScreen extends ConsumerStatefulWidget {
   const SearchScreen({super.key, this.accountId});
   final String? accountId;
@@ -79,7 +84,7 @@ class _SearchScreenState extends ConsumerState<SearchScreen> {
       ).wait;
 
       final matchedMailboxes = allMailboxes
-          .where((m) => m.name.toLowerCase().contains(ql))
+          .where((m) => _hasWordPrefix(m.name, ql))
           .toList()
         ..sort(compareMailboxes);
 
@@ -91,8 +96,9 @@ class _SearchScreenState extends ConsumerState<SearchScreen> {
         for (final addr in [...email.from, ...email.to, ...email.cc]) {
           final key = '${email.accountId}:${addr.email}';
           if (seen.contains(key)) continue;
-          final matchesEmail = addr.email.toLowerCase().contains(ql);
-          final matchesName = addr.name?.toLowerCase().contains(ql) ?? false;
+          final matchesEmail = _hasWordPrefix(addr.email, ql);
+          final matchesName =
+              addr.name != null && _hasWordPrefix(addr.name!, ql);
           if (!matchesEmail && !matchesName) continue;
           seen.add(key);
           final addrEmail = addr.email;

test/unit/email_repository_impl_test.dart

@@ -421,6 +421,38 @@ void main() {
       expect(results3, isEmpty);
     });
 
+    test('searchEmailsGlobal matches word prefix but not suffix', () async {
+      final r = _makeRepos();
+      await r.accounts.addAccount(_account, 'pw');
+
+      await r.db.into(r.db.emails).insert(
+            EmailsCompanion.insert(
+              id: 'acc-1:1',
+              accountId: 'acc-1',
+              mailboxPath: 'INBOX',
+              uid: 1,
+              subject: const Value('foobar baz'),
+              receivedAt: DateTime(2024),
+            ),
+          );
+      await r.db.into(r.db.emails).insert(
+            EmailsCompanion.insert(
+              id: 'acc-1:2',
+              accountId: 'acc-1',
+              mailboxPath: 'INBOX',
+              uid: 2,
+              subject: const Value('blafoo baz'),
+              receivedAt: DateTime(2024),
+            ),
+          );
+
+      // 'foo' is a prefix of 'foobar' — should match; 'blafoo' is not a
+      // prefix match so only one result expected.
+      final results = await r.emails.searchEmailsGlobal(null, 'foo');
+      expect(results, hasLength(1));
+      expect(results.first.subject, 'foobar baz');
+    });
+
     test('searchAddresses returns results sorted by most recently used',
         () async {
       final r = _makeRepos();

test/widget/search_screen_test.dart

@@ -160,6 +160,80 @@ void main() {
       expect(find.text('Archive'), findsOneWidget);
     });
 
+    testWidgets('folder with query as word prefix is matched', (tester) async {
+      const foobarMailbox = Mailbox(
+        id: 'acc-1:Foobar',
+        accountId: 'acc-1',
+        path: 'Foobar',
+        name: 'Foobar',
+        unreadCount: 0,
+        totalCount: 0,
+      );
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/search',
+          overrides: [
+            accountRepositoryProvider.overrideWithValue(
+              FakeAccountRepository([kTestAccount]),
+            ),
+            mailboxRepositoryProvider.overrideWithValue(
+              FakeMailboxRepository([foobarMailbox]),
+            ),
+            emailRepositoryProvider.overrideWithValue(FakeEmailRepository()),
+            searchHistoryRepositoryProvider.overrideWithValue(
+              FakeSearchHistoryRepository(),
+            ),
+          ],
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await tester.enterText(find.byType(TextField), 'foo');
+      await tester.pump(const Duration(milliseconds: 400));
+      await tester.pumpAndSettle();
+
+      expect(find.text('Folders'), findsOneWidget);
+      expect(find.text('Foobar'), findsOneWidget);
+    });
+
+    testWidgets('folder whose name ends with query is not matched', (
+      tester,
+    ) async {
+      const blafooMailbox = Mailbox(
+        id: 'acc-1:Blafoo',
+        accountId: 'acc-1',
+        path: 'Blafoo',
+        name: 'Blafoo',
+        unreadCount: 0,
+        totalCount: 0,
+      );
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/search',
+          overrides: [
+            accountRepositoryProvider.overrideWithValue(
+              FakeAccountRepository([kTestAccount]),
+            ),
+            mailboxRepositoryProvider.overrideWithValue(
+              FakeMailboxRepository([blafooMailbox]),
+            ),
+            emailRepositoryProvider.overrideWithValue(FakeEmailRepository()),
+            searchHistoryRepositoryProvider.overrideWithValue(
+              FakeSearchHistoryRepository(),
+            ),
+          ],
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await tester.enterText(find.byType(TextField), 'foo');
+      await tester.pump(const Duration(milliseconds: 400));
+      await tester.pumpAndSettle();
+
+      expect(find.text('Blafoo'), findsNothing);
+      expect(find.text('No results'), findsOneWidget);
+    });
+
     testWidgets('tapping clear button resets results to placeholder', (
       tester,
     ) async {