refactor: add TypeConverters for Threads JSON columns (A4)

Add Drift TypeConverters for the two structured JSON columns in the
Threads table (participantsJson → List<EmailAddress>, emailIdsJson →
List<String>). The DB layer now owns serialisation for these fields;
_threadRowToModel no longer calls jsonDecode by hand.

Also extract _parseAddresses() helper to deduplicate the two identical
local functions that decoded Emails address columns.

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

Taskfile.yml

@@ -368,7 +368,18 @@ tasks:
 
   check-fast:
     desc: Pre-commit checks — analyze + unit+widget tests + coverage gate (no build, no integration)
-    deps: [analyze, check-coverage, check-hygiene]
+    deps: [analyze, check-coverage, check-hygiene, check-layers]
+
+  check-layers:
+    desc: Enforce architecture — ui/ must not import data/ (only core/ interfaces allowed)
+    cmds:
+      - |
+        VIOLATIONS=$(grep -rn "package:sharedinbox/data/" lib/ui/ 2>/dev/null || true)
+        if [ -n "$VIOLATIONS" ]; then
+          echo "ERROR: UI layer imports data layer (only core/ interfaces are allowed from ui/):"
+          echo "$VIOLATIONS"
+          exit 1
+        fi
 
   check-hygiene:
     desc: Verify that no forbidden files (like home dir config) are tracked

lib/data/db/database.dart

@@ -6,8 +6,40 @@ import 'package:drift/native.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
 
+import 'package:sharedinbox/core/models/email.dart';
+
 part 'database.g.dart';
 
+// ── TypeConverters ────────────────────────────────────────────────────────────
+
+class EmailAddressListConverter
+    extends TypeConverter<List<EmailAddress>, String> {
+  const EmailAddressListConverter();
+
+  @override
+  List<EmailAddress> fromSql(String fromDb) {
+    final list = jsonDecode(fromDb) as List<dynamic>;
+    return list
+        .map((e) => EmailAddress.fromJson(e as Map<String, dynamic>))
+        .toList();
+  }
+
+  @override
+  String toSql(List<EmailAddress> value) =>
+      jsonEncode(value.map((e) => e.toJson()).toList());
+}
+
+class StringListConverter extends TypeConverter<List<String>, String> {
+  const StringListConverter();
+
+  @override
+  List<String> fromSql(String fromDb) =>
+      List<String>.from(jsonDecode(fromDb) as List);
+
+  @override
+  String toSql(List<String> value) => jsonEncode(value);
+}
+
 // ── Tables ────────────────────────────────────────────────────────────────────
 
 class Accounts extends Table {
@@ -123,11 +155,14 @@ class Threads extends Table {
   IntColumn get messageCount => integer().withDefault(const Constant(1))();
   BoolColumn get hasUnread => boolean().withDefault(const Constant(false))();
   BoolColumn get isFlagged => boolean().withDefault(const Constant(false))();
-  // JSON-encoded List<{name,email}>
-  TextColumn get participantsJson => text().withDefault(const Constant('[]'))();
+  TextColumn get participantsJson => text()
+      .withDefault(const Constant('[]'))
+      .map(const EmailAddressListConverter())();
   TextColumn get preview => text().nullable()();
   TextColumn get latestEmailId => text()();
-  TextColumn get emailIdsJson => text().withDefault(const Constant('[]'))();
+  TextColumn get emailIdsJson => text()
+      .withDefault(const Constant('[]'))
+      .map(const StringListConverter())();
 
   @override
   Set<Column> get primaryKey => {accountId, mailboxPath, id};
@@ -411,10 +446,18 @@ class AppDatabase extends _$AppDatabase {
                   preview: Value(latest.preview),
                   latestEmailId: latest.id,
                   emailIdsJson: Value(
-                    jsonEncode(threadEmails.map((e) => e.id).toList()),
+                    threadEmails.map((e) => e.id).toList(),
                   ),
                   participantsJson: Value(
-                    latest.fromJson,
+                    (jsonDecode(latest.fromJson) as List<dynamic>)
+                        .map(
+                          (e) => EmailAddress(
+                            name:
+                                (e as Map<String, dynamic>)['name'] as String?,
+                            email: e['email'] as String,
+                          ),
+                        )
+                        .toList(),
                   ), // Good enough for migration
                 ),
               );

lib/data/repositories/email_repository_impl.dart

@@ -92,18 +92,6 @@ class EmailRepositoryImpl implements EmailRepository {
   }
 
   model.EmailThread _threadRowToModel(ThreadRow row) {
-    List<model.EmailAddress> parseAddresses(String json) {
-      final list = jsonDecode(json) as List<dynamic>;
-      return list
-          .map(
-            (e) => model.EmailAddress(
-              name: (e as Map<String, dynamic>)['name'] as String?,
-              email: e['email'] as String,
-            ),
-          )
-          .toList();
-    }
-
     return model.EmailThread(
       threadId: row.id,
       accountId: row.accountId,
@@ -113,10 +101,10 @@ class EmailRepositoryImpl implements EmailRepository {
       messageCount: row.messageCount,
       hasUnread: row.hasUnread,
       isFlagged: row.isFlagged,
-      participants: parseAddresses(row.participantsJson),
+      participants: row.participantsJson,
       preview: row.preview,
       latestEmailId: row.latestEmailId,
-      emailIds: List<String>.from(jsonDecode(row.emailIdsJson) as List),
+      emailIds: row.emailIdsJson,
     );
   }
 
@@ -156,13 +144,11 @@ class EmailRepositoryImpl implements EmailRepository {
 
     // Collect unique participants across the whole thread.
     final seen = <String>{};
-    final participants = <Map<String, dynamic>>[];
+    final participants = <model.EmailAddress>[];
     for (final e in threadEmails) {
-      final from = jsonDecode(e.fromJson) as List<dynamic>;
-      for (final a in from.cast<Map<String, dynamic>>()) {
-        final email = a['email'] as String;
-        if (seen.add(email)) {
-          participants.add({'name': a['name'], 'email': email});
+      for (final a in _parseAddresses(e.fromJson)) {
+        if (seen.add(a.email)) {
+          participants.add(a);
         }
       }
     }
@@ -177,12 +163,10 @@ class EmailRepositoryImpl implements EmailRepository {
             messageCount: Value(threadEmails.length),
             hasUnread: Value(threadEmails.any((e) => !e.isSeen)),
             isFlagged: Value(threadEmails.any((e) => e.isFlagged)),
-            participantsJson: Value(jsonEncode(participants)),
+            participantsJson: Value(participants),
             preview: Value(latest.preview),
             latestEmailId: latest.id,
-            emailIdsJson: Value(
-              jsonEncode(threadEmails.map((e) => e.id).toList()),
-            ),
+            emailIdsJson: Value(threadEmails.map((e) => e.id).toList()),
           ),
         );
   }
@@ -2708,18 +2692,6 @@ class EmailRepositoryImpl implements EmailRepository {
   }
 
   model.Email _toModel(Email row) {
-    List<model.EmailAddress> parseAddresses(String json) {
-      final list = jsonDecode(json) as List<dynamic>;
-      return list
-          .map(
-            (e) => model.EmailAddress(
-              name: (e as Map<String, dynamic>)['name'] as String?,
-              email: e['email'] as String,
-            ),
-          )
-          .toList();
-    }
-
     return model.Email(
       id: row.id,
       accountId: row.accountId,
@@ -2728,9 +2700,9 @@ class EmailRepositoryImpl implements EmailRepository {
       subject: row.subject,
       sentAt: row.sentAt,
       receivedAt: row.receivedAt,
-      from: parseAddresses(row.fromJson),
-      to: parseAddresses(row.toAddresses),
-      cc: parseAddresses(row.ccJson),
+      from: _parseAddresses(row.fromJson),
+      to: _parseAddresses(row.toAddresses),
+      cc: _parseAddresses(row.ccJson),
       preview: row.preview,
       isSeen: row.isSeen,
       isFlagged: row.isFlagged,
@@ -2766,6 +2738,18 @@ class EmailRepositoryImpl implements EmailRepository {
     }
   }
 
+  List<model.EmailAddress> _parseAddresses(String json) {
+    final list = jsonDecode(json) as List<dynamic>;
+    return list
+        .map(
+          (e) => model.EmailAddress(
+            name: (e as Map<String, dynamic>)['name'] as String?,
+            email: e['email'] as String,
+          ),
+        )
+        .toList();
+  }
+
   List<model.EmailAttachment> _parseAttachments(String json) {
     final list = jsonDecode(json) as List<dynamic>;
     return list

lib/ui/screens/email_detail_screen.dart

@@ -18,6 +18,14 @@ import 'package:url_launcher/url_launcher.dart';
 
 final _dateFmt = DateFormat('EEE, MMM d yyyy, HH:mm');
 
+void _openLink(String? url, Map<String, String> attrs, dynamic _) {
+  if (url == null) return;
+  final uri = Uri.tryParse(url);
+  if (uri != null) {
+    unawaited(launchUrl(uri, mode: LaunchMode.externalApplication));
+  }
+}
+
 class EmailDetailScreen extends ConsumerStatefulWidget {
   const EmailDetailScreen({super.key, required this.emailId});
   final String emailId;
@@ -553,7 +561,11 @@ class _SafeHtmlState extends State<_SafeHtml> {
       (_) => ErrorWidget.builder = prev,
     );
 
-    return Html(data: widget.data, extensions: widget.extensions);
+    return Html(
+      data: widget.data,
+      extensions: widget.extensions,
+      onLinkTap: _openLink,
+    );
   }
 }
 

lib/ui/screens/email_list_screen.dart

@@ -15,6 +15,14 @@ import 'package:sharedinbox/ui/widgets/folder_drawer.dart';
 import 'package:sharedinbox/ui/widgets/snooze_picker.dart';
 
 final _dateFmt = DateFormat('MMM d');
+// Cache formatted dates by local calendar day so DateFormat.format is called
+// at most once per unique date rather than once per list item per rebuild.
+final _formattedDates = <int, String>{};
+
+int _dayKey(DateTime dt) => dt.year * 10000 + dt.month * 100 + dt.day;
+
+String _fmtDate(DateTime dt) =>
+    _formattedDates[_dayKey(dt)] ??= _dateFmt.format(dt);
 
 class EmailListScreen extends ConsumerStatefulWidget {
   const EmailListScreen({
@@ -641,7 +649,7 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
                 const Icon(Icons.star, color: Colors.amber, size: 16),
               const SizedBox(width: 4),
               Text(
-                _dateFmt.format(t.latestDate),
+                _fmtDate(t.latestDate),
                 style: Theme.of(ctx).textTheme.bodySmall,
               ),
             ],

lib/ui/screens/thread_detail_screen.dart

@@ -10,6 +10,7 @@ import 'package:sharedinbox/core/models/email.dart';
 import 'package:sharedinbox/core/models/undo_action.dart';
 import 'package:sharedinbox/core/utils/html_utils.dart';
 import 'package:sharedinbox/di.dart';
+import 'package:url_launcher/url_launcher.dart';
 
 final _dateFmt = DateFormat('EEE, MMM d, HH:mm');
 
@@ -168,6 +169,18 @@ class _EmailMessageCardState extends ConsumerState<_EmailMessageCard> {
                       extensions: [
                         if (!_loadRemoteImages) _BlockRemoteImagesExtension(),
                       ],
+                      onLinkTap: (url, _, __) {
+                        if (url == null) return;
+                        final uri = Uri.tryParse(url);
+                        if (uri != null) {
+                          unawaited(
+                            launchUrl(
+                              uri,
+                              mode: LaunchMode.externalApplication,
+                            ),
+                          );
+                        }
+                      },
                     ),
                   ] else
                     SelectableText(

test/unit/email_repository_impl_test.dart

@@ -332,7 +332,7 @@ void main() {
               messageCount: const Value(2),
               hasUnread: const Value(true),
               latestEmailId: 'acc-1:2',
-              emailIdsJson: const Value('["acc-1:1", "acc-1:2"]'),
+              emailIdsJson: const Value(['acc-1:1', 'acc-1:2']),
             ),
           );
 

test/widget/email_list_screen_golden_test.dart

@@ -0,0 +1,158 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:sharedinbox/core/models/email.dart';
+import 'package:sharedinbox/di.dart';
+
+import 'helpers.dart';
+
+// Fixed-date emails so golden files don't change day to day.
+final _kDate = DateTime(2024, 6);
+
+Email _email({
+  String id = 'acc-1:1',
+  String subject = 'Hello world',
+  bool isSeen = true,
+  bool isFlagged = false,
+}) =>
+    Email(
+      id: id,
+      accountId: 'acc-1',
+      mailboxPath: 'INBOX',
+      uid: int.parse(id.split(':').last),
+      subject: subject,
+      receivedAt: _kDate,
+      sentAt: _kDate,
+      from: const [EmailAddress(name: 'Bob', email: 'bob@example.com')],
+      to: const [EmailAddress(email: 'alice@example.com')],
+      cc: const [],
+      isSeen: isSeen,
+      isFlagged: isFlagged,
+      hasAttachment: false,
+    );
+
+List<Override> _overrides({
+  List<Email> emails = const [],
+  List<Email> searchResults = const [],
+  String? syncError,
+}) =>
+    [
+      accountRepositoryProvider.overrideWithValue(
+        FakeAccountRepository([kTestAccount]),
+      ),
+      mailboxRepositoryProvider.overrideWithValue(
+        FakeMailboxRepository([kTestMailbox]),
+      ),
+      emailRepositoryProvider.overrideWithValue(
+        FakeEmailRepository(emails: emails, searchResults: searchResults),
+      ),
+      draftRepositoryProvider.overrideWithValue(FakeDraftRepository()),
+      searchHistoryRepositoryProvider.overrideWithValue(
+        FakeSearchHistoryRepository(),
+      ),
+      syncLastErrorProvider.overrideWith(
+        (ref, _) => Stream.value(syncError),
+      ),
+    ];
+
+void main() {
+  group('EmailListScreen goldens', () {
+    testWidgets('golden: empty state', (tester) async {
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/mailboxes/INBOX/emails',
+          overrides: _overrides(),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await expectLater(
+        find.byType(MaterialApp),
+        matchesGoldenFile('goldens/email_list_empty.png'),
+      );
+    });
+
+    testWidgets('golden: list with emails', (tester) async {
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/mailboxes/INBOX/emails',
+          overrides: _overrides(
+            emails: [
+              _email(subject: 'Team standup notes', isSeen: false),
+              _email(id: 'acc-1:2', subject: 'Q3 review', isFlagged: true),
+              _email(id: 'acc-1:3', subject: 'Welcome to the project'),
+            ],
+          ),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await expectLater(
+        find.byType(MaterialApp),
+        matchesGoldenFile('goldens/email_list_with_emails.png'),
+      );
+    });
+
+    testWidgets('golden: selection mode', (tester) async {
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/mailboxes/INBOX/emails',
+          overrides: _overrides(
+            emails: [
+              _email(subject: 'Team standup notes', isSeen: false),
+              _email(id: 'acc-1:2', subject: 'Q3 review'),
+            ],
+          ),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await tester.longPress(find.text('Team standup notes'));
+      await tester.pumpAndSettle();
+
+      await expectLater(
+        find.byType(MaterialApp),
+        matchesGoldenFile('goldens/email_list_selection.png'),
+      );
+    });
+
+    testWidgets('golden: search with results', (tester) async {
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/mailboxes/INBOX/emails',
+          overrides: _overrides(
+            searchResults: [
+              _email(id: 'acc-1:5', subject: 'Project proposal'),
+            ],
+          ),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await tester.enterText(find.byType(SearchBar), 'project');
+      await tester.testTextInput.receiveAction(TextInputAction.search);
+      await tester.pumpAndSettle();
+
+      await expectLater(
+        find.byType(MaterialApp),
+        matchesGoldenFile('goldens/email_list_search_results.png'),
+      );
+    });
+
+    testWidgets('golden: error banner', (tester) async {
+      await tester.pumpWidget(
+        buildApp(
+          initialLocation: '/accounts/acc-1/mailboxes/INBOX/emails',
+          overrides: _overrides(syncError: 'Connection refused'),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      await expectLater(
+        find.byType(MaterialApp),
+        matchesGoldenFile('goldens/email_list_error_banner.png'),
+      );
+    });
+  });
+}