Replace ProjectCacheService null Project crash with diagnostic telemetry

src/Build/BackEnd/Components/ProjectCache/ProjectCacheService.cs

@@ -24,6 +24,7 @@
 using Microsoft.Build.Graph;
 using Microsoft.Build.Internal;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Framework.Telemetry;
 using ExceptionHandling = Microsoft.Build.Framework.ExceptionHandling;
 
 #pragma warning disable CS0618 // Type or member is obsolete, this class is adapting to both Experimental and new plugin APIs
@@ -816,9 +817,32 @@ public async Task HandleBuildResultAsync(
                 requestConfiguration.RetrieveFromCache();
             }
 
-            // Now we are sure the Project property is available, verify it's not null before proceeding.
-            // If it's null, it means the configuration is not properly loaded, which should not happen at this stage. 
-            ErrorUtilities.VerifyThrowInternalNull(requestConfiguration.Project, nameof(requestConfiguration.Project));
+            // The Project property may be null if the configuration was created from a remote node
+            // request or the project was never loaded locally (e.g., in VS scenario where ShouldUseCache
+            // returns true before checking IsLoaded). Skip cache result handling in this case.
+            if (requestConfiguration.Project is null)
+            {
+                string projectCacheState = string.Join(":",
+                    requestConfiguration.ConfigurationId,
+                    Path.GetFileName(requestConfiguration.ProjectFullPath),
+                    requestConfiguration.IsLoaded,
+                    requestConfiguration.IsCached,
+                    requestConfiguration.WasGeneratedByNode,
+                    _isVsScenario,
+                    _globalProjectCacheDescriptor is not null);
+
+                CrashTelemetryRecorder.EmitEndBuildHangDiagnostics(new CrashTelemetry
+                {
+                    ExitType = CrashExitType.ProjectCacheFailure,
+                    ExceptionMessage = "Project unexpectedly null in HandleBuildResultAsync",
+                    BuildEngineVersion = Evaluation.ProjectCollection.Version?.ToString(),
+                    BuildEngineFrameworkName = NativeMethodsShared.FrameworkName,
+                    BuildEngineHost = BuildEnvironmentState.GetHostName(),
+                    IsStandaloneExecution = false,
+                    ProjectCacheState = projectCacheState,
+                });
+                return;
+            }
 
             // Filter to plugins which apply to the project, if any
             List<ProjectCacheDescriptor> projectCacheDescriptors = GetProjectCacheDescriptors(requestConfiguration.Project).ToList();

src/Framework/Telemetry/CrashTelemetry.cs

@@ -353,6 +353,12 @@ internal class CrashTelemetry : TelemetryBase, IActivityTelemetryDataHolder
     /// </summary>
     public string? ActiveNodeDetails { get; set; }
 
+    /// <summary>
+    /// Diagnostic state of the project cache configuration when Project is unexpectedly null.
+    /// Format: "configId:projectFileName:IsLoaded:IsCached:WasGeneratedByNode:IsVsScenario:HasGlobalPlugins".
+    /// </summary>
+    public string? ProjectCacheState { get; set; }
+
     // --- Build state diagnostic properties (help diagnose the context of the crash) ---
 
     /// <summary>
@@ -533,6 +539,7 @@ public Dictionary<string, object> GetActivityProperties()
         AddIfNotNull(ActiveNodeIds);
         AddIfNotNull(EnableNodeReuse);
         AddIfNotNull(ActiveNodeDetails);
+        AddIfNotNull(ProjectCacheState);
 
         // Build state diagnostic properties
         AddIfNotNull(IsStandaloneExecution);
@@ -602,6 +609,7 @@ public override IDictionary<string, string> GetProperties()
         AddIfNotNull(ActiveNodeIds);
         AddIfNotNull(EnableNodeReuse?.ToString(), nameof(EnableNodeReuse));
         AddIfNotNull(ActiveNodeDetails);
+        AddIfNotNull(ProjectCacheState);
 
         // Build state diagnostic properties
         AddIfNotNull(IsStandaloneExecution?.ToString(), nameof(IsStandaloneExecution));