diff --git a/lib/api/model/events.dart b/lib/api/model/events.dart
index c604ecdb0c..344be5950f 100644
--- a/lib/api/model/events.dart
+++ b/lib/api/model/events.dart
@@ -341,7 +341,7 @@ class UpdateMessageEvent extends Event {
   final bool? renderingOnly; // TODO(server-5)
   final int messageId;
   final List<int> messageIds;
-  final List<String> flags; // TODO enum
+  final List<MessageFlag> flags;
   final int? editTimestamp; // TODO(server-5)
   final String? streamName;
   final int? streamId;
diff --git a/lib/api/model/events.g.dart b/lib/api/model/events.g.dart
index fe1e5b8367..53aff1c708 100644
--- a/lib/api/model/events.g.dart
+++ b/lib/api/model/events.g.dart
@@ -166,7 +166,9 @@ UpdateMessageEvent _$UpdateMessageEventFromJson(Map<String, dynamic> json) =>
       messageId: json['message_id'] as int,
       messageIds:
           (json['message_ids'] as List<dynamic>).map((e) => e as int).toList(),
-      flags: (json['flags'] as List<dynamic>).map((e) => e as String).toList(),
+      flags: (json['flags'] as List<dynamic>)
+          .map((e) => $enumDecode(_$MessageFlagEnumMap, e))
+          .toList(),
       editTimestamp: json['edit_timestamp'] as int?,
       streamName: json['stream_name'] as String?,
       streamId: json['stream_id'] as int?,
@@ -204,6 +206,17 @@ Map<String, dynamic> _$UpdateMessageEventToJson(UpdateMessageEvent instance) =>
       'is_me_message': instance.isMeMessage,
     };
 
+const _$MessageFlagEnumMap = {
+  MessageFlag.read: 'read',
+  MessageFlag.starred: 'starred',
+  MessageFlag.collapsed: 'collapsed',
+  MessageFlag.mentioned: 'mentioned',
+  MessageFlag.wildcardMentioned: 'wildcard_mentioned',
+  MessageFlag.hasAlertWord: 'has_alert_word',
+  MessageFlag.historical: 'historical',
+  MessageFlag.unknown: 'unknown',
+};
+
 const _$PropagateModeEnumMap = {
   PropagateMode.changeOne: 'change_one',
   PropagateMode.changeLater: 'change_later',
diff --git a/lib/api/model/model.dart b/lib/api/model/model.dart
index 3ebd8fee16..b74a713f6f 100644
--- a/lib/api/model/model.dart
+++ b/lib/api/model/model.dart
@@ -271,10 +271,16 @@ sealed class Message {
 
   // final List<TopicLink> topicLinks; // TODO handle
   // final string type; // handled by runtime type of object
-  List<String> flags; // TODO enum
+  @JsonKey(fromJson: _flagsFromJson)
+  List<MessageFlag> flags; // Unrecognized flags won't roundtrip through {to,from}Json.
   final String? matchContent;
   final String? matchSubject;
 
+  static List<MessageFlag> _flagsFromJson(dynamic json) {
+    final list = json as List<dynamic>;
+    return list.map((raw) => MessageFlag.fromRawString(raw as String)).toList();
+  }
+
   Message({
     required this.client,
     required this.content,
@@ -305,6 +311,32 @@ sealed class Message {
   Map<String, dynamic> toJson();
 }
 
+/// As in [Message.flags].
+@JsonEnum(fieldRename: FieldRename.snake, alwaysCreate: true)
+enum MessageFlag {
+  read,
+  starred,
+  collapsed,
+  mentioned,
+  wildcardMentioned,
+  hasAlertWord,
+  historical,
+  unknown;
+
+  /// Get a [MessageFlag] from a raw, snake-case string.
+  ///
+  /// Will be [MessageFlag.unknown] if we don't recognize the string.
+  ///
+  /// Example:
+  ///   'wildcard_mentioned' -> Flag.wildcardMentioned
+  static MessageFlag fromRawString(String raw) => _byRawString[raw] ?? unknown;
+
+  // _$…EnumMap is thanks to `alwaysCreate: true` and `fieldRename: FieldRename.snake`
+  static final _byRawString = _$MessageFlagEnumMap.map((key, value) => MapEntry(value, key));
+
+  String toJson() => _$MessageFlagEnumMap[this]!;
+}
+
 @JsonSerializable(fieldRename: FieldRename.snake)
 class StreamMessage extends Message {
   @override
diff --git a/lib/api/model/model.g.dart b/lib/api/model/model.g.dart
index 452a5a4fc4..e8d1e7eb24 100644
--- a/lib/api/model/model.g.dart
+++ b/lib/api/model/model.g.dart
@@ -196,7 +196,7 @@ StreamMessage _$StreamMessageFromJson(Map<String, dynamic> json) =>
       senderRealmStr: json['sender_realm_str'] as String,
       subject: json['subject'] as String,
       timestamp: json['timestamp'] as int,
-      flags: (json['flags'] as List<dynamic>).map((e) => e as String).toList(),
+      flags: Message._flagsFromJson(json['flags']),
       matchContent: json['match_content'] as String?,
       matchSubject: json['match_subject'] as String?,
       displayRecipient: json['display_recipient'] as String,
@@ -257,7 +257,7 @@ DmMessage _$DmMessageFromJson(Map<String, dynamic> json) => DmMessage(
       senderRealmStr: json['sender_realm_str'] as String,
       subject: json['subject'] as String,
       timestamp: json['timestamp'] as int,
-      flags: (json['flags'] as List<dynamic>).map((e) => e as String).toList(),
+      flags: Message._flagsFromJson(json['flags']),
       matchContent: json['match_content'] as String?,
       matchSubject: json['match_subject'] as String?,
       displayRecipient: const DmRecipientListConverter()
@@ -306,3 +306,14 @@ const _$ReactionTypeEnumMap = {
   ReactionType.realmEmoji: 'realm_emoji',
   ReactionType.zulipExtraEmoji: 'zulip_extra_emoji',
 };
+
+const _$MessageFlagEnumMap = {
+  MessageFlag.read: 'read',
+  MessageFlag.starred: 'starred',
+  MessageFlag.collapsed: 'collapsed',
+  MessageFlag.mentioned: 'mentioned',
+  MessageFlag.wildcardMentioned: 'wildcard_mentioned',
+  MessageFlag.hasAlertWord: 'has_alert_word',
+  MessageFlag.historical: 'historical',
+  MessageFlag.unknown: 'unknown',
+};
diff --git a/lib/model/narrow.dart b/lib/model/narrow.dart
index 6076612561..c71cfe5407 100644
--- a/lib/model/narrow.dart
+++ b/lib/model/narrow.dart
@@ -161,6 +161,13 @@ class DmNarrow extends Narrow implements SendableNarrow {
     );
   }
 
+  factory DmNarrow.withUser(int userId, {required int selfUserId}) {
+    return DmNarrow(
+      allRecipientIds: {userId, selfUserId}.toList()..sort(),
+      selfUserId: selfUserId,
+    );
+  }
+
   /// The user IDs of everyone in the conversation, sorted.
   ///
   /// Each message in the conversation is sent by one of these users
diff --git a/test/api/model/events_test.dart b/test/api/model/events_test.dart
index e86cc1c4c4..d5e2be1708 100644
--- a/test/api/model/events_test.dart
+++ b/test/api/model/events_test.dart
@@ -2,6 +2,7 @@ import 'package:checks/checks.dart';
 import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/initial_snapshot.dart';
+import 'package:zulip/api/model/model.dart';
 
 import '../../example_data.dart' as eg;
 import '../../stdlib_checks.dart';
@@ -11,15 +12,15 @@ import 'model_checks.dart';
 void main() {
   test('message: move flags into message object', () {
     final message = eg.streamMessage();
-    MessageEvent mkEvent(List<String> flags) => Event.fromJson({
+    MessageEvent mkEvent(List<MessageFlag> flags) => Event.fromJson({
       'type': 'message',
       'id': 1,
       'message': message.toJson()..remove('flags'),
-      'flags': flags,
+      'flags': flags.map((f) => f.toJson()).toList(),
     }) as MessageEvent;
     check(mkEvent(message.flags)).message.jsonEquals(message);
     check(mkEvent([])).message.flags.deepEquals([]);
-    check(mkEvent(['read'])).message.flags.deepEquals(['read']);
+    check(mkEvent([MessageFlag.read])).message.flags.deepEquals([MessageFlag.read]);
   });
 
   test('user_settings: all known settings have event handling', () {
diff --git a/test/api/model/model_checks.dart b/test/api/model/model_checks.dart
index 7067e53d84..13bab49afd 100644
--- a/test/api/model/model_checks.dart
+++ b/test/api/model/model_checks.dart
@@ -6,7 +6,7 @@ extension MessageChecks on Subject<Message> {
   Subject<bool> get isMeMessage => has((e) => e.isMeMessage, 'isMeMessage');
   Subject<int?> get lastEditTimestamp => has((e) => e.lastEditTimestamp, 'lastEditTimestamp');
   Subject<List<Reaction>> get reactions => has((e) => e.reactions, 'reactions');
-  Subject<List<String>> get flags => has((e) => e.flags, 'flags');
+  Subject<List<MessageFlag>> get flags => has((e) => e.flags, 'flags');
 
   // TODO accessors for other fields
 }
diff --git a/test/api/model/model_test.dart b/test/api/model/model_test.dart
index 6ccf59c545..e97293427b 100644
--- a/test/api/model/model_test.dart
+++ b/test/api/model/model_test.dart
@@ -3,6 +3,8 @@ import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/model.dart';
 
 import '../../example_data.dart' as eg;
+import '../../stdlib_checks.dart';
+import 'model_checks.dart';
 
 void main() {
   group('User', () {
@@ -47,6 +49,22 @@ void main() {
     });
   });
 
+  group('Message', () {
+    test('no crash on unrecognized flag', () {
+      final m1 = Message.fromJson(
+        (deepToJson(eg.streamMessage()) as Map<String, dynamic>)
+          ..['flags'] = ['read', 'something_unknown'],
+      );
+      check(m1).flags.deepEquals([MessageFlag.read, MessageFlag.unknown]);
+
+      final m2 = Message.fromJson(
+        (deepToJson(eg.dmMessage(from: eg.selfUser, to: [eg.otherUser])) as Map<String, dynamic>)
+          ..['flags'] = ['read', 'something_unknown'],
+      );
+      check(m2).flags.deepEquals([MessageFlag.read, MessageFlag.unknown]);
+    });
+  });
+
   group('DmMessage', () {
     final Map<String, dynamic> baseJson = Map.unmodifiable(
       eg.dmMessage(from: eg.otherUser, to: [eg.selfUser]).toJson());
diff --git a/test/model/message_list_test.dart b/test/model/message_list_test.dart
index 6dfca6e4de..9c1160bbb1 100644
--- a/test/model/message_list_test.dart
+++ b/test/model/message_list_test.dart
@@ -269,7 +269,7 @@ void main() async {
         id: 1,
         messageId: originalMessage.id,
         messageIds: [originalMessage.id],
-        flags: ["starred"],
+        flags: [MessageFlag.starred],
         renderedContent: "<p>Hello, edited</p>",
         editTimestamp: 99999,
         isMeMessage: true,
diff --git a/test/model/narrow_test.dart b/test/model/narrow_test.dart
index be15e3adf2..c7825c6766 100644
--- a/test/model/narrow_test.dart
+++ b/test/model/narrow_test.dart
@@ -69,6 +69,27 @@ void main() {
         selfUserId: eg.selfUser.userId));
     });
 
+    test('withUser: same user', () {
+      final actual = DmNarrow.withUser(5, selfUserId: 5);
+      check(actual).equals(DmNarrow(
+        allRecipientIds: [5],
+        selfUserId: 5));
+    });
+
+    test('withUser: user ID less than selfUserId', () {
+      final actual = DmNarrow.withUser(3, selfUserId: 5);
+      check(actual).equals(DmNarrow(
+          allRecipientIds: [3, 5],
+          selfUserId: 5));
+    });
+
+    test('withUser: user ID greater than selfUserId', () {
+      final actual = DmNarrow.withUser(7, selfUserId: 5);
+      check(actual).equals(DmNarrow(
+          allRecipientIds: [5, 7],
+          selfUserId: 5));
+    });
+
     test('otherRecipientIds', () {
       check(DmNarrow(allRecipientIds: [1, 2, 3], selfUserId: 2))
         .otherRecipientIds.deepEquals([1, 3]);
diff --git a/test/stdlib_checks.dart b/test/stdlib_checks.dart
index e2d05657e1..2829c92ec5 100644
--- a/test/stdlib_checks.dart
+++ b/test/stdlib_checks.dart
@@ -57,7 +57,7 @@ Object? deepToJson(Object? object) {
     case List():
       result = object.map((x) => deepToJson(x)).toList();
     case Map() when object.keys.every((k) => k is String):
-      result = object.map((k, v) => MapEntry(k, deepToJson(v)));
+      result = object.map((k, v) => MapEntry<String, dynamic>(k, deepToJson(v)));
     default:
       return (null, false);
   }