feat: report why play mode stopped in control-play-mode responses

.agents/skills/uloop-control-play-mode/SKILL.md

@@ -32,6 +32,8 @@ Returns JSON with the current play mode state:
 - `ResumedFromPause`: Whether `Play` resumed a paused Play Mode session instead of starting a new one
 - `Message`: Description of the action performed
 - `Warning`: Set when the action carries a caveat. A fresh `Play` start always notes that the session started from Edit-time scene state; additionally, when active hot-reload patches or enabled pause points exist and Domain Reload is enabled, it reports how many of them the Play-entry domain reload will discard.
+- `StoppedBy` (string, optional): Why Play Mode last stopped: `cli-control-play-mode`, `cli-compile-stop-setting`, `cli-run-tests-cancel`, `script-compilation`, or `unknown`. Present on `Stop` when Play Mode was already stopped, and on `Status` when Play Mode is not running. Omitted when this Editor session has no confirmed stop.
+- `StoppedAt` (string, optional): UTC ISO 8601 timestamp of that stop. Omitted together with `StoppedBy` when no stop is recorded.
 
 ## Notes
 

.claude/skills/uloop-control-play-mode/SKILL.md

@@ -32,6 +32,8 @@ Returns JSON with the current play mode state:
 - `ResumedFromPause`: Whether `Play` resumed a paused Play Mode session instead of starting a new one
 - `Message`: Description of the action performed
 - `Warning`: Set when the action carries a caveat. A fresh `Play` start always notes that the session started from Edit-time scene state; additionally, when active hot-reload patches or enabled pause points exist and Domain Reload is enabled, it reports how many of them the Play-entry domain reload will discard.
+- `StoppedBy` (string, optional): Why Play Mode last stopped: `cli-control-play-mode`, `cli-compile-stop-setting`, `cli-run-tests-cancel`, `script-compilation`, or `unknown`. Present on `Stop` when Play Mode was already stopped, and on `Status` when Play Mode is not running. Omitted when this Editor session has no confirmed stop.
+- `StoppedAt` (string, optional): UTC ISO 8601 timestamp of that stop. Omitted together with `StoppedBy` when no stop is recorded.
 
 ## Notes
 

Assets/Tests/Editor/ControlPlayModeStoppedByTests.cs

@@ -0,0 +1,200 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using NUnit.Framework;
+using UnityEditor;
+
+using io.github.hatayama.UnityCliLoop.FirstPartyTools;
+using io.github.hatayama.UnityCliLoop.ToolContracts;
+
+namespace io.github.hatayama.UnityCliLoop.Tests.Editor
+{
+    /// <summary>
+    /// Tests that control-play-mode copies confirmed stop reasons onto Stop and Status responses.
+    /// </summary>
+    public sealed class ControlPlayModeStoppedByTests
+    {
+        [SetUp]
+        public void SetUp()
+        {
+            PlayModeStopReasonSessionStore.ClearForTests();
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            PlayModeStopReasonSessionStore.ClearForTests();
+        }
+
+        /// <summary>
+        /// What: Stop while already stopped copies the confirmed SessionState reason onto the response.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenStopAlreadyStoppedAndReasonConfirmed_CopiesStoppedByAndStoppedAt()
+        {
+            Assert.That(EditorApplication.isPlaying, Is.False);
+            PlayModeStopReasonSessionStore.SetPending("cli-control-play-mode");
+            PlayModeStopReasonSessionStore.ConfirmPending("2026-01-01T00:00:00.0000000Z");
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                compilationFailureProvider: new EmptyCompilationFailureProvider(),
+                compilationFailureGate: new OpenCompilationFailureGate());
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Stop
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(response.WasAlreadyStopped, Is.True);
+            Assert.That(response.StoppedBy, Is.EqualTo("cli-control-play-mode"));
+            Assert.That(response.StoppedAt, Is.EqualTo("2026-01-01T00:00:00.0000000Z"));
+        }
+
+        /// <summary>
+        /// What: Status while Play Mode is stopped copies the confirmed SessionState reason onto the response.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenStatusWhileStoppedAndReasonConfirmed_CopiesStoppedByAndStoppedAt()
+        {
+            Assert.That(EditorApplication.isPlaying, Is.False);
+            PlayModeStopReasonSessionStore.SetPending("cli-compile-stop-setting");
+            PlayModeStopReasonSessionStore.ConfirmPending("2026-01-03T00:00:00.0000000Z");
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                compilationFailureProvider: new EmptyCompilationFailureProvider(),
+                compilationFailureGate: new OpenCompilationFailureGate());
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Status
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(response.IsPlaying, Is.False);
+            Assert.That(response.StoppedBy, Is.EqualTo("cli-compile-stop-setting"));
+            Assert.That(response.StoppedAt, Is.EqualTo("2026-01-03T00:00:00.0000000Z"));
+        }
+
+        /// <summary>
+        /// What: Stop while already stopped omits StoppedBy when SessionState has no confirmed reason.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenStopAlreadyStoppedAndNoRecord_LeavesStoppedByNull()
+        {
+            Assert.That(EditorApplication.isPlaying, Is.False);
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                compilationFailureProvider: new EmptyCompilationFailureProvider(),
+                compilationFailureGate: new OpenCompilationFailureGate());
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Stop
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(response.WasAlreadyStopped, Is.True);
+            Assert.That(response.StoppedBy, Is.Null);
+            Assert.That(response.StoppedAt, Is.Null);
+        }
+
+        /// <summary>
+        /// What: serialized JSON omits StoppedBy and StoppedAt when they are null, and includes them when set.
+        /// </summary>
+        [Test]
+        public void ControlPlayModeResponse_WhenSerialized_OmitsNullStoppedByAndStoppedAtKeys()
+        {
+            ControlPlayModeResponse omitted = new ControlPlayModeResponse
+            {
+                Message = "Play mode was already stopped",
+                Warning = string.Empty,
+                CompileErrors = Array.Empty<ControlPlayModeCompileError>()
+            };
+            JObject omittedJson = JObject.Parse(
+                JsonConvert.SerializeObject(
+                    omitted,
+                    Formatting.None,
+                    UnityCliLoopJsonResponseSerializerSettings.Settings));
+            Assert.That(omittedJson.Property("StoppedBy"), Is.Null);
+            Assert.That(omittedJson.Property("StoppedAt"), Is.Null);
+
+            ControlPlayModeResponse populated = new ControlPlayModeResponse
+            {
+                Message = "Play mode was already stopped",
+                Warning = string.Empty,
+                CompileErrors = Array.Empty<ControlPlayModeCompileError>(),
+                StoppedBy = "cli-control-play-mode",
+                StoppedAt = "2026-01-01T00:00:00.0000000Z"
+            };
+            JObject populatedJson = LoadJsonWithoutDateParsing(
+                JsonConvert.SerializeObject(
+                    populated,
+                    Formatting.None,
+                    UnityCliLoopJsonResponseSerializerSettings.Settings));
+            Assert.That(populatedJson["StoppedBy"]?.Value<string>(), Is.EqualTo("cli-control-play-mode"));
+            Assert.That(populatedJson["StoppedAt"]?.Value<string>(), Is.EqualTo("2026-01-01T00:00:00.0000000Z"));
+        }
+
+        /// <summary>
+        /// What: Stop with a changing stop does not copy StoppedBy even when a record exists.
+        /// </summary>
+        [Test]
+        public async Task ExecuteAsync_WhenStopWhilePlaying_DoesNotCopyStoppedBy()
+        {
+            PlayModeStopReasonSessionStore.SetPending("script-compilation");
+            PlayModeStopReasonSessionStore.ConfirmPending("2026-01-04T00:00:00.0000000Z");
+            FakePlayingEditorStateService editorState = new FakePlayingEditorStateService();
+            ControlPlayModeUseCase useCase = new ControlPlayModeUseCase(
+                compilationFailureProvider: new EmptyCompilationFailureProvider(),
+                compilationFailureGate: new OpenCompilationFailureGate(),
+                editorStateService: editorState);
+            ControlPlayModeSchema schema = new ControlPlayModeSchema
+            {
+                Action = PlayModeAction.Stop
+            };
+
+            ControlPlayModeResponse response = await useCase.ExecuteAsync(schema, CancellationToken.None);
+
+            Assert.That(response.WasAlreadyStopped, Is.False);
+            Assert.That(response.StoppedBy, Is.Null);
+            Assert.That(response.StoppedAt, Is.Null);
+        }
+
+        private static JObject LoadJsonWithoutDateParsing(string json)
+        {
+            using (StringReader stringReader = new StringReader(json))
+            using (JsonTextReader jsonReader = new JsonTextReader(stringReader))
+            {
+                jsonReader.DateParseHandling = DateParseHandling.None;
+                return JObject.Load(jsonReader);
+            }
+        }
+
+        private sealed class EmptyCompilationFailureProvider : IControlPlayModeCompilationFailureProvider
+        {
+            public ControlPlayModeCompileError[] GetLastFailedErrors()
+            {
+                return Array.Empty<ControlPlayModeCompileError>();
+            }
+        }
+
+        private sealed class OpenCompilationFailureGate : IControlPlayModeCompilationFailureGate
+        {
+            public bool HasScriptCompilationFailed()
+            {
+                return false;
+            }
+        }
+
+        private sealed class FakePlayingEditorStateService : IControlPlayModeEditorStateService
+        {
+            public bool IsPlaying { get; set; } = true;
+            public bool IsPaused { get; set; }
+
+            public void Step()
+            {
+            }
+        }
+    }
+}