fix: address Copilot review comments on PR #456/#458

- Remove empty try/finally block in ClientUpdateStrategy download path
- Add thread-safety note for shared custom executor in DefaultDownloadOrchestrator
- Add ResolveExtensionType<T>() to avoid wasteful instantiation for pipeline factory
- Restore ClientUpdateStrategy(IDownloadOrchestrator?) constructor for backward compat

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: JusterZhu

src/c#/GeneralUpdate.Core/Bootstrap/GeneralUpdateBootstrap.cs

@@ -109,11 +109,11 @@ private async Task<GeneralUpdateBootstrap> LaunchWithStrategy(IStrategy roleStra
             var downloadExecutor = ResolveExtension<Download.Abstractions.IDownloadExecutor>();
 
             // Build download pipeline factory from registered extension type
+            // Uses ResolveExtensionType to avoid wasteful instantiation just to get the Type
             Func<string?, Download.Abstractions.IDownloadPipeline>? downloadPipelineFactory = null;
-            var downloadPipeline = ResolveExtension<Download.Abstractions.IDownloadPipeline>();
-            if (downloadPipeline != null)
+            var pipelineType = ResolveExtensionType<Download.Abstractions.IDownloadPipeline>();
+            if (pipelineType != null)
             {
-                var pipelineType = downloadPipeline.GetType();
                 var stringCtor = pipelineType.GetConstructor([typeof(string)]);
                 if (stringCtor != null)
                     downloadPipelineFactory = hash => (Download.Abstractions.IDownloadPipeline)stringCtor.Invoke([hash]);

src/c#/GeneralUpdate.Core/Configuration/AbstractBootstrap.cs

@@ -109,5 +109,11 @@ protected T GetOption<T>(UpdateOption<T>? option)
                 return instance as TExtension;
             return null;
         }
+
+        /// <summary>Resolves the registered extension type without instantiating it.</summary>
+        protected Type? ResolveExtensionType<TExtension>() where TExtension : class
+        {
+            return _extensions.TryGetValue(typeof(TExtension), out var t) ? t : null;
+        }
     }
 }

src/c#/GeneralUpdate.Core/Download/Orchestrators/DefaultDownloadOrchestrator.cs

@@ -30,6 +30,9 @@ public class DefaultDownloadOrchestrator : IDownloadOrchestrator
     private readonly DownloadOrchestratorOptions _options;
     private readonly IDownloadExecutor? _customExecutor;
     private readonly Func<string?, IDownloadPipeline>? _pipelineFactory;
+    // Note: _customExecutor is a single shared instance used across parallel asset downloads.
+    // Implementations of IDownloadExecutor must be thread-safe. HttpClient-based executors
+    // satisfy this as HttpClient is designed for concurrent use.
 
     public DefaultDownloadOrchestrator(
         HttpClient httpClient,

src/c#/GeneralUpdate.Core/Strategy/ClientUpdateStrategy.cs

@@ -60,6 +60,9 @@ private enum UpdateScenario
 
     public ClientUpdateStrategy() { }
 
+    public ClientUpdateStrategy(Download.Abstractions.IDownloadOrchestrator? orchestrator)
+        => _orchestrator = orchestrator;
+
     /// <summary>Sets a custom OS-level strategy. When set, replaces automatic platform detection.</summary>
     public void SetOsStrategy(IStrategy? strategy) => _customOsStrategy = strategy;
 
@@ -264,14 +267,10 @@ private async Task ExecuteStandardWorkflowAsync()
         else
         {
             var httpClient = GeneralUpdate.Core.Network.HttpClientProvider.Shared;
-            try
-            {
-                var orchestrator = new Download.Orchestrators.DefaultDownloadOrchestrator(
-                    httpClient, orchOptions, _customDownloadPolicy,
-                    _customDownloadExecutor, _customDownloadPipelineFactory);
-                await orchestrator.ExecuteAsync(downloadPlan, _configInfo.TempPath).ConfigureAwait(false);
-            }
-            finally { }
+            var orchestrator = new Download.Orchestrators.DefaultDownloadOrchestrator(
+                httpClient, orchOptions, _customDownloadPolicy,
+                _customDownloadExecutor, _customDownloadPipelineFactory);
+            await orchestrator.ExecuteAsync(downloadPlan, _configInfo.TempPath).ConfigureAwait(false);
         }
 
         await SafeReportDownloadCompletedAsync(hooksCtx).ConfigureAwait(false);