Harden PlayMode test runs (CoplayDev#396)

* Harden PlayMode test runs

- Guard against starting tests while already in Play Mode.
- Pre-save dirty scenes before PlayMode runs to avoid SaveModifiedSceneTask failures.
- Temporarily disable domain reload during PlayMode tests to keep the MCP bridge alive; restore settings afterward.
- Avoid runSynchronously because it can freeze Unity

* Handle the not too uncommon case where we have an empty scene

Author: msanatan

MCPForUnity/Editor/Services/TestRunnerService.cs

@@ -5,8 +5,10 @@
 using System.Threading.Tasks;
 using MCPForUnity.Editor.Helpers;
 using UnityEditor;
+using UnityEditor.SceneManagement;
 using UnityEditor.TestTools.TestRunner.Api;
 using UnityEngine;
+using UnityEngine.SceneManagement;
 
 namespace MCPForUnity.Editor.Services
 {
@@ -31,7 +33,7 @@ public TestRunnerService()
 
         public async Task<IReadOnlyList<Dictionary<string, string>>> GetTestsAsync(TestMode? mode)
         {
-            await _operationLock.WaitAsync().ConfigureAwait(false);
+            await _operationLock.WaitAsync().ConfigureAwait(true);
             try
             {
                 var modes = mode.HasValue ? new[] { mode.Value } : AllModes;
@@ -58,25 +60,59 @@ public async Task<IReadOnlyList<Dictionary<string, string>>> GetTestsAsync(TestM
 
         public async Task<TestRunResult> RunTestsAsync(TestMode mode)
         {
-            await _operationLock.WaitAsync().ConfigureAwait(false);
+            await _operationLock.WaitAsync().ConfigureAwait(true);
             Task<TestRunResult> runTask;
+            bool adjustedPlayModeOptions = false;
+            bool originalEnterPlayModeOptionsEnabled = false;
+            EnterPlayModeOptions originalEnterPlayModeOptions = EnterPlayModeOptions.None;
             try
             {
                 if (_runCompletionSource != null && !_runCompletionSource.Task.IsCompleted)
                 {
                     throw new InvalidOperationException("A Unity test run is already in progress.");
                 }
 
+                if (EditorApplication.isPlaying || EditorApplication.isPlayingOrWillChangePlaymode)
+                {
+                    throw new InvalidOperationException("Cannot start a test run while the Editor is in or entering Play Mode. Stop Play Mode and try again.");
+                }
+
+                if (mode == TestMode.PlayMode)
+                {
+                    // PlayMode runs transition the editor into play across multiple update ticks. Unity's
+                    // built-in pipeline schedules SaveModifiedSceneTask early, but that task uses
+                    // EditorSceneManager.SaveCurrentModifiedScenesIfUserWantsTo which throws once play mode is
+                    // active. To minimize that window we pre-save dirty scenes and disable domain reload (so the
+                    // MCP bridge stays alive). We do NOT force runSynchronously here because that can freeze the
+                    // editor in some projects. If the TestRunner still hits the save task after entering play, the
+                    // run can fail; in that case, rerun from a clean Edit Mode state.
+                    adjustedPlayModeOptions = EnsurePlayModeRunsWithoutDomainReload(
+                        out originalEnterPlayModeOptionsEnabled,
+                        out originalEnterPlayModeOptions);
+                }
+
                 _leafResults.Clear();
                 _runCompletionSource = new TaskCompletionSource<TestRunResult>(TaskCreationOptions.RunContinuationsAsynchronously);
 
                 var filter = new Filter { testMode = mode };
-                _testRunnerApi.Execute(new ExecutionSettings(filter));
+                var settings = new ExecutionSettings(filter);
+
+                if (mode == TestMode.PlayMode)
+                {
+                    SaveDirtyScenesIfNeeded();
+                }
+
+                _testRunnerApi.Execute(settings);
 
                 runTask = _runCompletionSource.Task;
             }
             catch
             {
+                if (adjustedPlayModeOptions)
+                {
+                    RestoreEnterPlayModeOptions(originalEnterPlayModeOptionsEnabled, originalEnterPlayModeOptions);
+                }
+
                 _operationLock.Release();
                 throw;
             }
@@ -87,6 +123,11 @@ public async Task<TestRunResult> RunTestsAsync(TestMode mode)
             }
             finally
             {
+                if (adjustedPlayModeOptions)
+                {
+                    RestoreEnterPlayModeOptions(originalEnterPlayModeOptionsEnabled, originalEnterPlayModeOptions);
+                }
+
                 _operationLock.Release();
             }
         }
@@ -149,6 +190,60 @@ public void TestFinished(ITestResultAdaptor result)
 
         #endregion
 
+        private static bool EnsurePlayModeRunsWithoutDomainReload(
+            out bool originalEnterPlayModeOptionsEnabled,
+            out EnterPlayModeOptions originalEnterPlayModeOptions)
+        {
+            originalEnterPlayModeOptionsEnabled = EditorSettings.enterPlayModeOptionsEnabled;
+            originalEnterPlayModeOptions = EditorSettings.enterPlayModeOptions;
+
+            // When Play Mode triggers a domain reload, the MCP connection is torn down and the pending
+            // test run response never makes it back to the caller. To keep the bridge alive for this
+            // invocation, temporarily enable Enter Play Mode Options with domain reload disabled.
+            bool domainReloadDisabled = (originalEnterPlayModeOptions & EnterPlayModeOptions.DisableDomainReload) != 0;
+            bool needsChange = !originalEnterPlayModeOptionsEnabled || !domainReloadDisabled;
+            if (!needsChange)
+            {
+                return false;
+            }
+
+            var desired = originalEnterPlayModeOptions | EnterPlayModeOptions.DisableDomainReload;
+            EditorSettings.enterPlayModeOptionsEnabled = true;
+            EditorSettings.enterPlayModeOptions = desired;
+            return true;
+        }
+
+        private static void RestoreEnterPlayModeOptions(bool originalEnabled, EnterPlayModeOptions originalOptions)
+        {
+            EditorSettings.enterPlayModeOptions = originalOptions;
+            EditorSettings.enterPlayModeOptionsEnabled = originalEnabled;
+        }
+
+        private static void SaveDirtyScenesIfNeeded()
+        {
+            int sceneCount = SceneManager.sceneCount;
+            for (int i = 0; i < sceneCount; i++)
+            {
+                var scene = SceneManager.GetSceneAt(i);
+                if (scene.isDirty)
+                {
+                    if (string.IsNullOrEmpty(scene.path))
+                    {
+                        McpLog.Warn($"[TestRunnerService] Skipping unsaved scene '{scene.name}': save it manually before running PlayMode tests.");
+                        continue;
+                    }
+                    try
+                    {
+                        EditorSceneManager.SaveScene(scene);
+                    }
+                    catch (Exception ex)
+                    {
+                        McpLog.Warn($"[TestRunnerService] Failed to save dirty scene '{scene.name}': {ex.Message}");
+                    }
+                }
+            }
+        }
+
         #region Test list helpers
 
         private async Task<ITestAdaptor> RetrieveTestRootAsync(TestMode mode)