fix(app): gate startup coin icon precaching

lib/app_config/app_config.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:path_provider/path_provider.dart';
+import 'package:web_dex/common/screen.dart';
 
 const String mmRpcVersion = '2.0';
 // issue https://github.com/flutter/flutter/issues/19462#issuecomment-478284020
@@ -36,6 +37,10 @@ const bool isBitrefillIntegrationEnabled = false;
 ///! trading purposes where it is not legally compliant.
 const bool kShowTradingWarning = false;
 
+/// Controls whether startup coin icon precaching is enabled.
+/// Defaults to web-only via the compile-time platform constant.
+bool get kEnableCoinIconPrecache => kIsWeb && isMobile;
+
 const Duration kPerformanceLogInterval = Duration(minutes: 1);
 
 /// Enable debug logging for electrum connections and RPC methods.

lib/bloc/app_bloc_root.dart

@@ -359,6 +359,10 @@ class _MyAppViewState extends State<_MyAppView> {
   void didChangeDependencies() {
     super.didChangeDependencies();
 
+    if (!kEnableCoinIconPrecache) {
+      return;
+    }
+
     final sdk = RepositoryProvider.of<KomodoDefiSdk>(context);
     _precacheCoinIcons(sdk).ignore();
   }
@@ -392,19 +396,19 @@ class _MyAppViewState extends State<_MyAppView> {
     }
   }
 
-  Completer<void>? _currentPrecacheOperation;
+  Future<void>? _currentPrecacheOperation;
 
-  Future<void> _precacheCoinIcons(KomodoDefiSdk sdk) async {
-    if (_currentPrecacheOperation != null &&
-        !_currentPrecacheOperation!.isCompleted) {
-      // completeError throws an uncaught exception, which causes the UI
-      // tests to fail when switching between light and dark theme
-      log('New request to precache icons started.');
-      _currentPrecacheOperation!.complete();
+  Future<void> _precacheCoinIcons(KomodoDefiSdk sdk) {
+    final currentPrecacheOperation = _currentPrecacheOperation;
+    if (currentPrecacheOperation != null) {
+      log('Coin icon precache already started, reusing existing operation.');
+      return currentPrecacheOperation;
     }
 
-    _currentPrecacheOperation = Completer<void>();
+    return _currentPrecacheOperation = _runCoinIconPrecache(sdk);
+  }
 
+  Future<void> _runCoinIconPrecache(KomodoDefiSdk sdk) async {
     try {
       final stopwatch = Stopwatch()..start();
       final availableAssetIds = sdk.assets.available.keys.where(
@@ -417,7 +421,6 @@ class _MyAppViewState extends State<_MyAppView> {
         // not mounted and return early with error.
         // ignore: use_build_context_synchronously
         // if (context.findRenderObject() == null) {
-        //   _currentPrecacheOperation!.completeError('Build context is stale.');
         //   return;
         // }
 
@@ -428,8 +431,6 @@ class _MyAppViewState extends State<_MyAppView> {
         ).onError((_, __) => debugPrint('Error precaching coin icon $assetId'));
       }
 
-      _currentPrecacheOperation!.complete();
-
       if (!mounted) return;
       context.read<AnalyticsBloc>().logEvent(
         CoinsDataUpdatedEventData(
@@ -440,7 +441,7 @@ class _MyAppViewState extends State<_MyAppView> {
       );
     } catch (e) {
       log('Error precaching coin icons: $e');
-      _currentPrecacheOperation!.completeError(e);
+      rethrow;
     }
   }
 }