Fix TerminalLogger crash when ProjectStarted arrives without prior evaluation event

src/Build.UnitTests/TerminalLogger_Tests.cs

@@ -1070,5 +1070,35 @@ public async Task DisplayNodesRestoresStatusAfterMSBuildTaskYields_TestProject(b
 
             await Verify(_outputWriter.ToString(), _settings).UniqueForOSPlatform().UseParameters(runOnCentralNode);
         }
+
+        /// <summary>
+        /// Tests that TerminalLogger handles ProjectStarted events without a prior ProjectEvaluationFinished event.
+        /// This scenario can occur in multithreaded builds with taskhosts where the evaluation event may not be received
+        /// before the project started event.
+        /// </summary>
+        [Fact]
+        public void ProjectStartedWithoutEvaluation_DoesNotCrash()
+        {
+            // Start the build
+            _centralNodeEventSource.InvokeBuildStarted(MakeBuildStartedEventArgs());
+
+            // Intentionally skip the evaluation finished event to simulate a multithreaded build scenario
+            // where ProjectStarted arrives before (or without) ProjectEvaluationFinished
+            var buildContext = MakeBuildEventContext(evalId: -1, projectContextId: 1); // Use invalid eval ID
+
+            // This should not throw or crash
+            _centralNodeEventSource.InvokeProjectStarted(MakeProjectStartedEventArgs(_projectFile, buildEventContext: buildContext));
+
+            // Verify we can continue with the build
+            _centralNodeEventSource.InvokeTargetStarted(MakeTargetStartedEventArgs(_projectFile, "Build", buildEventContext: buildContext));
+            _centralNodeEventSource.InvokeTaskStarted(MakeTaskStartedEventArgs(_projectFile, "Task", buildEventContext: buildContext));
+            _centralNodeEventSource.InvokeTaskFinished(MakeTaskFinishedEventArgs(_projectFile, "Task", true, buildEventContext: buildContext));
+            _centralNodeEventSource.InvokeTargetFinished(MakeTargetFinishedEventArgs(_projectFile, "Build", true, buildEventContext: buildContext));
+            _centralNodeEventSource.InvokeProjectFinished(MakeProjectFinishedEventArgs(_projectFile, true, buildEventContext: buildContext));
+            _centralNodeEventSource.InvokeBuildFinished(MakeBuildFinishedEventArgs(true));
+
+            // If we got here without crashing, the test passed
+            _outputWriter.ToString().ShouldNotBeNull();
+        }
     }
 }

src/Build/Logging/TerminalLogger/TerminalLogger.cs

@@ -722,7 +722,12 @@ private void ProjectStarted(object sender, ProjectStartedEventArgs e)
                 targetFramework = evalInfo.TargetFramework;
                 runtimeIdentifier = evalInfo.RuntimeIdentifier;
             }
-            System.Diagnostics.Debug.Assert(evalInfo != default, "EvalProjectInfo should have been captured before ProjectStarted");
+            else
+            {
+                // In some scenarios (e.g., multithreaded builds with taskhosts), the evaluation event
+                // may not have been received before the project started event. Create a fallback.
+                evalInfo = new EvalProjectInfo(evalContext, e.ProjectFile, null, null);
+            }
 
             TerminalProjectInfo projectInfo = new(c, evalInfo, _createStopwatch?.Invoke());
             _projects[c] = projectInfo;