fix(jellyfin): stop overriding a server subtitle mode of None

Jellyfin answers PlaybackInfo with a null DefaultSubtitleStreamIndex when the
user's SubtitleMode is None: the index is the server's whole answer, and null
means it picked no subtitle. The mapper read null as "the server did not say"
and promoted the container's default/forced flags to a server selection
instead, which outranks the profile subtitle mode in the selection ladder. A
viewer who had turned subtitles off for their Jellyfin user got them switched
back on by every item that carried a default or forced row.

Only the row the server names is selected now. A stream the viewer picks, and
an explicit off, still survive per item because Plezy reports the index
through playback progress and the server hands it back as that index or -1.

close #1779

test/services/jellyfin_media_info_test.dart

@@ -75,17 +75,42 @@ void main() {
       expect(jpn.languageCode, 'jpn');
       expect(jpn.selected, isFalse);
 
-      // Subtitle, external + forced
+      // Subtitle, external + forced. Forced is metadata about the row, not a
+      // selection: this source carries no DefaultSubtitleStreamIndex, so
+      // nothing may claim the server picked it.
       final sub = info.subtitleTracks.single;
       expect(sub.id, 3);
       expect(sub.codec, 'srt');
       expect(sub.languageCode, 'eng');
       expect(sub.forced, isTrue);
-      expect(sub.selected, isTrue);
+      expect(sub.selected, isFalse);
       expect(sub.isExternal, isTrue);
       expect(sub.key, '/Videos/src-1/Subtitles/3/Stream.srt');
     });
 
+    test('no DefaultSubtitleStreamIndex means no server-selected subtitle (#1779)', () {
+      // What Jellyfin answers for a user whose SubtitleMode is None: the
+      // container still flags a default/forced row, the server still declines
+      // to select one. Promoting those flags to a selection outranked the
+      // user's own "no subtitles" setting in the selection ladder.
+      final info = jellyfinMediaSourceToMediaSourceInfo({
+        'Id': 'src-1',
+        'DefaultSubtitleStreamIndex': null,
+        'MediaStreams': [
+          {'Index': 1, 'Type': 'Audio', 'Language': 'eng', 'IsDefault': true},
+          {'Index': 3, 'Type': 'Subtitle', 'Language': 'eng', 'IsDefault': true, 'IsForced': true},
+          {'Index': 4, 'Type': 'Subtitle', 'Language': 'eng'},
+        ],
+      });
+
+      expect(info.defaultSubtitleStreamIndex, isNull);
+      expect(info.subtitleTracks.map((track) => track.selected), [false, false]);
+      // The row metadata itself is untouched; only the selection claim is.
+      expect(info.subtitleTracks.first.forced, isTrue);
+      // Audio keeps the container default: something always has to play.
+      expect(info.audioTracks.single.selected, isTrue);
+    });
+
     test('maps display criteria from Jellyfin video stream metadata', () {
       final info = jellyfinMediaSourceToMediaSourceInfo({
         'Id': 'src-1',

test/services/playback_subtitle_resolver_test.dart

@@ -2,7 +2,9 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:plezy/media/media_backend.dart';
 import 'package:plezy/media/media_kind.dart';
 import 'package:plezy/media/media_source_info.dart';
+import 'package:plezy/models/jellyfin/jellyfin_user_profile.dart';
 import 'package:plezy/mpv/mpv.dart';
+import 'package:plezy/services/jellyfin_media_info_mapper.dart';
 import 'package:plezy/services/playback_initialization_types.dart';
 import 'package:plezy/services/playback_subtitle_resolver.dart';
 import 'package:plezy/services/subtitle_preference.dart';
@@ -238,6 +240,59 @@ void main() {
     expect(result.sidecarsAtOpen, isEmpty);
   });
 
+  group('Jellyfin server subtitle answer', () {
+    // Verbatim shape of a direct-played episode from a real Jellyfin server:
+    // the container flags one row default+forced, and the response carries the
+    // index the server picked for this user (null when it picked none).
+    MediaSourceInfo jellyfinInfo({Object? defaultSubtitleStreamIndex}) => jellyfinMediaSourceToMediaSourceInfo({
+      'Id': 'src-1',
+      'DefaultSubtitleStreamIndex': defaultSubtitleStreamIndex,
+      'MediaStreams': [
+        {'Index': 1, 'Type': 'Audio', 'Language': 'eng', 'IsDefault': true},
+        {'Index': 3, 'Type': 'Subtitle', 'Language': 'eng', 'Codec': 'ass', 'IsDefault': true, 'IsForced': true},
+        {'Index': 4, 'Type': 'Subtitle', 'Language': 'eng', 'Codec': 'ass'},
+      ],
+    });
+
+    JellyfinUserProfile profileWithMode(String mode) => JellyfinUserProfile.fromUserDto({
+      'Configuration': {'SubtitleMode': mode, 'PlayDefaultAudioTrack': true},
+    });
+
+    test('a user who turned subtitles off on the server gets none (#1779)', () {
+      final result = PlaybackSubtitleResolver.resolve(
+        metadata: metadata,
+        mediaInfo: jellyfinInfo(),
+        sidecars: const [],
+        profileSettings: profileWithMode('None'),
+      );
+
+      expect(result.isOff, isTrue);
+    });
+
+    test('the stream the server did pick still plays', () {
+      final result = PlaybackSubtitleResolver.resolve(
+        metadata: metadata,
+        mediaInfo: jellyfinInfo(defaultSubtitleStreamIndex: 3),
+        sidecars: const [],
+        profileSettings: profileWithMode('Default'),
+      );
+
+      expect(result.isOff, isFalse);
+      expect(result.primarySourceStreamId, 3);
+    });
+
+    test('an off persisted through progress reports plays nothing', () {
+      final result = PlaybackSubtitleResolver.resolve(
+        metadata: metadata,
+        mediaInfo: jellyfinInfo(defaultSubtitleStreamIndex: -1),
+        sidecars: const [],
+        profileSettings: profileWithMode('Default'),
+      );
+
+      expect(result.isOff, isTrue);
+    });
+  });
+
   test('retains each source metadata row for a shared preloaded container', () {
     final result = PlaybackSubtitleResolver.resolve(
       metadata: metadata,