MobileFix - Resilience: Background retry policy for failed mutations (Part 1 of 6)

Problem Statement

No retry/backoff for failed mutations; add queue.

Files to Modify / Create (static targets)

• lib/services/retry_queue.dart
• lib/services/**
• test/unit/services/retry_queue_test.dart

Files to Modify / Create (detected for this PR)

• [ ] lib/main.dart
• [ ] lib/models/post/post_model.dart
• [ ] lib/plugin/plugin_injector.dart
• [ ] lib/plugin/readme/files.md
• [ ] lib/plugin/registry.dart
• [ ] lib/services/caching/base_feed_manager.dart
• [ ] lib/services/caching/offline_action_queue.dart
• [ ] lib/services/chat_subscription_service.dart
• [ ] lib/services/comment_service.dart
• [ ] lib/services/database_mutation_functions.dart

Proposed Solution

Implement within MVVM + Provider + GetIt; avoid large rewrites. Keep changes scoped to the listed files.

Implementation Approach

1. Update only the files listed above (<= 10 in this PR).
2. Add/adjust tests accordingly; keep CI green.
3. If more files are needed, open follow-up PRs.

Acceptance Criteria

• [ ] All listed files updated
• [ ] Tests added/updated (>= 80% for changed units)
• [ ] CI passing
• [ ] Docs updated if applicable

Starter Code

Starter Code

// lib/services/retry_queue.dart
import 'dart:async';
typedef Task<T>=Future<T> Function();
class RetryQueue{
  static final Map<String,Task<dynamic>> _q={};
  static Future<T> enqueue<T>(Task<T> task,{required String key,Duration initial=const Duration(milliseconds:300)}) async{
    _q[key]=task; var delay=initial;
    for(var i=0;i<3;i++){ try{ final r=await task(); _q.remove(key); return r; }catch(_){ await Future.delayed(delay); delay*=2; } }
    rethrow;
  }
}

Dependencies

• Blocked by: #3183
• Blocks: #3204

Phase

P2 - High Impact