Avoid trying to use _hotReloadAgent variable before it is initialized (#46916)

* trying to fix 45190

* change initialization order

* keeping old \n

* keeping the comment

* keeping the comment

* addressing @tmat comment

---------

Co-authored-by: Thays Grazia <[email protected]>

Author: thaystg

src/Components/WebAssembly/WebAssembly/src/HotReload/WebAssemblyHotReload.cs

@@ -26,11 +26,6 @@ public static class WebAssemblyHotReload
 
     internal static async Task InitializeAsync()
     {
-        // Analyzer has a bug where it doesn't handle ConditionalAttribute: https://github.com/dotnet/roslyn/issues/63464
-#pragma warning disable IDE0200 // Remove unnecessary lambda expression
-        _hotReloadAgent = new HotReloadAgent(m => Debug.WriteLine(m));
-#pragma warning restore IDE0200 // Remove unnecessary lambda expression
-
         if (Environment.GetEnvironmentVariable("__ASPNETCORE_BROWSER_TOOLS") == "true")
         {
             // Attempt to read previously applied hot reload deltas if the ASP.NET Core browser tools are available (indicated by the presence of the Environment variable).
@@ -50,14 +45,19 @@ internal static async Task InitializeAsync()
     [JSInvokable(nameof(ApplyHotReloadDelta))]
     public static void ApplyHotReloadDelta(string moduleIdString, byte[] metadataDelta, byte[] ilDelta, byte[] pdbBytes)
     {
+        // Analyzer has a bug where it doesn't handle ConditionalAttribute: https://github.com/dotnet/roslyn/issues/63464
+#pragma warning disable IDE0200 // Remove unnecessary lambda expression
+        Interlocked.CompareExchange(ref _hotReloadAgent, new HotReloadAgent(m => Debug.WriteLine(m)), null);
+#pragma warning restore IDE0200 // Remove unnecessary lambda expression
+
         var moduleId = Guid.Parse(moduleIdString, CultureInfo.InvariantCulture);
 
         _updateDeltas[0].ModuleId = moduleId;
         _updateDeltas[0].MetadataDelta = metadataDelta;
         _updateDeltas[0].ILDelta = ilDelta;
         _updateDeltas[0].PdbBytes = pdbBytes;
 
-        _hotReloadAgent!.ApplyDeltas(_updateDeltas);
+        _hotReloadAgent.ApplyDeltas(_updateDeltas);
     }
 
     /// <summary>