## Problem Statement Errors surface inconsistently across services; ViewModels special-case handling; tests cannot assert a uniform failure path. ## Files to Modify / Create (static targets) - lib/utils/result.dart - lib/utils/app_failure.dart - lib/utils/gql_helper.dart - lib/services/** - test/unit/utils/** - test/service_tests/** ## 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 (extensive) Before: ```dart final res = await client.mutate(MutationOptions(document: gql(doc), variables: vars)); if (res.hasException) throw res.exception!; return res.data!; ``` After: ```dart // lib/utils/result.dart abstract class Result{const Result();R when({required R Function(T) ok,required R Function(E) err});} class Ok extends Result{final T v; const Ok(this.v); @override R when({required R Function(T) ok,required R Function(E) err})=>ok(v);} class Err extends Result{final E e; const Err(this.e); @override R when({required R Function(T) ok,required R Function(E) err})=>err(e);} // lib/utils/app_failure.dart class AppFailure{final String code; final String message; final Object? cause; const AppFailure({required this.code,required this.message,this.cause}); static AppFailure network([Object? e])=>AppFailure(code:'network',message:'Temporary network error',cause:e); static AppFailure auth([Object? e]) =>AppFailure(code:'auth', message:'Authentication required',cause:e); static AppFailure unknown([Object? e])=>AppFailure(code:'unknown',message:'Unexpected error',cause:e); // lib/utils/gql_helper.dart import 'package:graphql_flutter/graphql_flutter.dart'; import 'package:talawa/utils/result.dart'; import 'package:talawa/utils/app_failure.dart'; class GqlHelper{ static Future,AppFailure>> mutate( GraphQLClient c,String doc,Map vars) async{ try{ final r=await c.mutate(MutationOptions(document:gql(doc),variables:vars)); if(r.hasException){ return Err(AppFailure.network(r.exception!)); } return Ok(r.data ?? {}); }catch(e){ return Err(AppFailure.unknown(e)); } } static Future,AppFailure>> query( GraphQLClient c,String doc,Map vars) async{ try{ final r=await c.query(QueryOptions(document:gql(doc),variables:vars)); if(r.hasException){ return Err(AppFailure.network(r.exception!)); } return Ok(r.data ?? {}); }catch(e){ return Err(AppFailure.unknown(e)); } } } ``` ## Dependencies - Blocked by: None - Blocks: #3179 ## Phase P2 - High Impact

MobileFix - Architecture: Standardize a Result/Error model across services (Part 1 of 6) #3178

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