improved performance and battery usage on older devices

lib/api/marianumcloud/talk/chat/get_chat_cache.dart

@@ -17,7 +17,7 @@ class GetChatCache extends SimpleCache<GetChatResponse> {
              lookIntoFuture: GetChatParamsSwitch.off,
              setReadMarker: GetChatParamsSwitch.on,
              // Small initial page; also the per-chat offline snapshot written to
-             // localstore. Older messages are paged in on scroll-up via
+             // the request cache. Older messages are paged in on scroll-up via
              // GetChatHistory. Keep in sync with ChatBloc's _kInitialPageSize.
              limit: 50,
            ),

lib/api/marianumcloud/talk/chat/get_chat_history.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/foundation.dart';
 import 'package:http/http.dart' as http;
 
 import '../../../errors/server_exception.dart';
@@ -45,8 +46,10 @@ class GetChatHistory {
     final status = response.statusCode;
     if (status == 304) return null;
     if (status >= 200 && status < 300) {
-      return GetChatResponse.fromJson(NextcloudOcs.decode(response.body))
-        ..headers = response.headers;
+      // A page holds up to 200 messages and lands while the user is scrolling;
+      // decoding it on the UI isolate stalls the fling.
+      final parsed = await compute(_parseChatResponse, response.body);
+      return parsed..headers = response.headers;
     }
     throw ServerException(
       statusCode: status,
@@ -54,3 +57,6 @@ class GetChatHistory {
     );
   }
 }
+
+GetChatResponse _parseChatResponse(String body) =>
+    GetChatResponse.fromJson(NextcloudOcs.decode(body));

lib/api/marianumcloud/talk/room/get_room.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/foundation.dart';
 import 'package:http/http.dart' as http;
 
 import '../../nextcloud_ocs.dart';
@@ -10,8 +11,12 @@ class GetRoom extends TalkApi<GetRoomResponse> {
   GetRoom(this.params) : super('v4/room', null, getParameters: params.toJson());
 
   @override
-  GetRoomResponse assemble(String raw) =>
-      GetRoomResponse.fromJson(NextcloudOcs.decode(raw));
+  GetRoomResponse assemble(String raw) => _parseRooms(raw);
+
+  // The room list with status is 100–250 KB and polled every 15–60 s.
+  @override
+  Future<GetRoomResponse> assembleAsync(String raw) =>
+      compute(_parseRooms, raw);
 
   @override
   Future<http.Response> request(
@@ -20,3 +25,6 @@ class GetRoom extends TalkApi<GetRoomResponse> {
     Map<String, String>? headers,
   ) => http.get(uri, headers: headers);
 }
+
+GetRoomResponse _parseRooms(String raw) =>
+    GetRoomResponse.fromJson(NextcloudOcs.decode(raw));

lib/api/marianumcloud/talk/talk_api.dart

@@ -30,6 +30,10 @@ abstract class TalkApi<T extends ApiResponse?> {
   );
   T assemble(String raw);
 
+  /// Override to parse large payloads off the UI isolate (e.g. via `compute`
+  /// with a top-level parser); defaults to the synchronous [assemble].
+  Future<T> assembleAsync(String raw) async => assemble(raw);
+
   Future<T> run() async {
     final endpoint = NextcloudOcs.uri(
       'apps/spreed/api/$path',
@@ -69,7 +73,7 @@ abstract class TalkApi<T extends ApiResponse?> {
     }
 
     try {
-      final assembled = assemble(data.body);
+      final assembled = await assembleAsync(data.body);
       assembled?.headers = data.headers;
       return assembled;
     } catch (e) {