fix: make control-play-mode report an already-running Play session as a no-op

Assets/Tests/Editor/ControlPlayModeUseCaseTests.cs

@@ -493,6 +493,125 @@ public async Task ExecuteAsync_WhenPlayResumesFromPause_OnlyClearsPauseAndReport
             Assert.That(quietSaver.SaveCallCount, Is.EqualTo(0));
         }
 
+        /// <summary>
+        /// What: Play while already running and not paused is a no-op with the already-running message.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenPlayWhileAlreadyRunning_ReportsNoOpWithoutSideEffects()
+        {
+            FakeControlPlayModeEditorStateService editorState = new(isPlaying: true, isPaused: false);
+            StubEditorUnsavedChangesQuietSaver quietSaver = new(
+                saveFailures: System.Array.Empty<string>(),
+                remainingAfterSave: System.Array.Empty<string>());
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                new StubCompilationFailureProvider(System.Array.Empty<ControlPlayModeCompileError>()),
+                new StubCompilationFailureGate(false),
+                quietSaver,
+                editorState,
+                new StubDomainReloadDropStateProvider());
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Play,
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(
+                response.Message,
+                Is.EqualTo("Play mode was already running; nothing to start or resume."));
+            Assert.That(response.Changed, Is.False);
+            Assert.That(response.ResumedFromPause, Is.False);
+            Assert.That(response.Warning, Is.Empty);
+            Assert.That(response.IsPlaying, Is.True);
+            Assert.That(response.IsPaused, Is.False);
+            Assert.That(editorState.IsPlayingSetCount, Is.EqualTo(0));
+            Assert.That(editorState.IsPausedSetCount, Is.EqualTo(0));
+            Assert.That(quietSaver.SaveCallCount, Is.EqualTo(0));
+        }
+
+        /// <summary>
+        /// What: Resume while already running and not paused uses the same no-op contract as Play.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenResumeWhileAlreadyRunning_ReportsNoOpWithoutSideEffects()
+        {
+            FakeControlPlayModeEditorStateService editorState = new(isPlaying: true, isPaused: false);
+            StubEditorUnsavedChangesQuietSaver quietSaver = new(
+                saveFailures: System.Array.Empty<string>(),
+                remainingAfterSave: System.Array.Empty<string>());
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                new StubCompilationFailureProvider(System.Array.Empty<ControlPlayModeCompileError>()),
+                new StubCompilationFailureGate(false),
+                quietSaver,
+                editorState,
+                new StubDomainReloadDropStateProvider());
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Resume,
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(
+                response.Message,
+                Is.EqualTo("Play mode was already running; nothing to start or resume."));
+            Assert.That(response.Changed, Is.False);
+            Assert.That(response.ResumedFromPause, Is.False);
+            Assert.That(response.Warning, Is.Empty);
+            Assert.That(response.IsPlaying, Is.True);
+            Assert.That(response.IsPaused, Is.False);
+            Assert.That(editorState.IsPlayingSetCount, Is.EqualTo(0));
+            Assert.That(editorState.IsPausedSetCount, Is.EqualTo(0));
+            Assert.That(quietSaver.SaveCallCount, Is.EqualTo(0));
+        }
+
+        /// <summary>
+        /// What: a failed compile gate does not replace the already-running no-op while Play is live.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenPlayWhileAlreadyRunningAndCompileFailed_ReportsNoOpNotCompileBlock()
+        {
+            FakeControlPlayModeEditorStateService editorState = new(isPlaying: true, isPaused: false);
+            StubEditorUnsavedChangesQuietSaver quietSaver = new(
+                saveFailures: System.Array.Empty<string>(),
+                remainingAfterSave: System.Array.Empty<string>());
+            ControlPlayModeCompileError[] compileErrors =
+            {
+                new ControlPlayModeCompileError
+                {
+                    Message = "CS1525: invalid expression",
+                    File = "Assets/Scripts/Sample.cs",
+                    Line = 3
+                }
+            };
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                new StubCompilationFailureProvider(compileErrors),
+                new StubCompilationFailureGate(true),
+                quietSaver,
+                editorState,
+                new StubDomainReloadDropStateProvider());
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Play,
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(
+                response.Message,
+                Is.EqualTo("Play mode was already running; nothing to start or resume."));
+            Assert.That(response.Changed, Is.False);
+            Assert.That(response.ResumedFromPause, Is.False);
+            Assert.That(response.Warning, Is.Empty);
+            Assert.That(response.IsPlaying, Is.True);
+            Assert.That(response.IsPaused, Is.False);
+            Assert.That(response.BlockedByCompileErrors, Is.False);
+            Assert.That(response.CompileErrorCount, Is.EqualTo(0));
+            Assert.That(editorState.IsPlayingSetCount, Is.EqualTo(0));
+            Assert.That(editorState.IsPausedSetCount, Is.EqualTo(0));
+            Assert.That(quietSaver.SaveCallCount, Is.EqualTo(0));
+        }
+
         [Test]
         public async Task ExecuteAsync_WhenPlayStartsFreshSession_SetsPlayingAndReportsWarning()
         {

Packages/src/Editor/FirstPartyTools/ControlPlayMode/ControlPlayModeConstants.cs

@@ -10,5 +10,8 @@ internal static class ControlPlayModeConstants
         internal const string StoppedByCliRunTestsCancel = "cli-run-tests-cancel";
         internal const string StoppedByScriptCompilation = "script-compilation";
         internal const string StoppedByUnknown = "unknown";
+
+        internal const string AlreadyRunningPlayMessage =
+            "Play mode was already running; nothing to start or resume.";
     }
 }

Packages/src/Editor/FirstPartyTools/ControlPlayMode/ControlPlayModeUseCase.cs

@@ -173,6 +173,16 @@ private ControlPlayModeActionResult ExecutePlayModeStart(bool wasPaused, bool wa
                     true);
             }
 
+            // Why: already-running Play used to report "Play mode started" even when Changed
+            // was false, which made a no-op look like a new session.
+            if (wasPlaying && !wasPaused)
+            {
+                return ControlPlayModeActionResult.FromState(
+                    ControlPlayModeConstants.AlreadyRunningPlayMessage,
+                    false,
+                    false);
+            }
+
             // Why only when entering Play from Edit: SaveScene does not work while already playing,
             // and resume-from-pause must not rewrite Scene assets.
             if (!wasPlaying)