Serialize lifecycle transitions

Tests/Cockpit.Benchmarks/SessionLoadingBenchmarks.cs

@@ -63,7 +63,7 @@
 				Context = new SdkSessionContext
 				{
 					// Mix of resolvable paths and null to exercise both normalization branches.
 					WorkingDirectory = i % 2 == 0 ? validDir : null,
 					GitRoot = i % 2 == 0 ? validDir : null,
 					Repository = i % 2 == 0 ? "owner/repo" : null,
 					Branch = i % 2 == 0 ? "main" : null
@@ -101,7 +101,7 @@
 					Title = metadata.Summary ?? $"Session {metadata.SessionId[..8]}",
 					CreatedAt = metadata.StartTime.UtcDateTime,
 					LastActivity = metadata.ModifiedTime.UtcDateTime,
-					Status = SessionStatusEnum.Idle,
+					AgentRunState = AgentRunStateEnum.Idle,
 					Model = _defaultModel,
 					ReasoningEffort = _defaultModel.DefaultReasoningEffort,
 					Context = new()

Tests/Cockpit.UnitTests/Features/Agents/AgentFeatureTests.cs

@@ -29,7 +29,7 @@ public void Dispose()
 	{
 		Id = Guid.NewGuid().ToString(),
 		Title = "Test",
-		Status = SessionStatusEnum.Idle,
+		AgentRunState = AgentRunStateEnum.Idle,
 		CreatedAt = DateTime.UtcNow,
 		LastActivity = DateTime.UtcNow,
 		Model = testModel,

Tests/Cockpit.UnitTests/Features/ElicitationRequests/ElicitationFeatureTests.cs

@@ -2,6 +2,7 @@
 using Cockpit.Features.ElicitationRequests;
 using Cockpit.Features.Permissions.Models;
 using Cockpit.Features.Sessions;
+using Cockpit.Features.Sessions.Interactions;
 using Cockpit.Features.Sessions.Models;
 using Cockpit.Features.UserInputRequests;
 using GitHub.Copilot;
@@ -39,7 +40,7 @@ sealed class TestSessionStateProvider : ISessionStateProvider
 		CreatedAt = DateTime.UtcNow,
 		LastActivity = DateTime.UtcNow,
 		Model = testModel,
-		Status = SessionStatusEnum.Idle,
+		AgentRunState = AgentRunStateEnum.Idle,
 		Context = new()
 		{
 			CurrentWorkingDirectory = "",
@@ -130,10 +131,10 @@ public async Task HandleElicitationRequest_SetsSessionStatusToNeedsElicitation()
 	}
 
 	[Fact]
-	public async Task HandleElicitationRequest_RestoredToPreviousStatusOnResolve()
+	public async Task HandleElicitationRequest_RevealsRunStateOnResolve()
 	{
 		(ElicitationFeature feature, SessionModel session, _) = CreateFeature();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 
 		(Task<ElicitationResult> handleTask, ElicitationRequestModel model) = await StartHandleAsync(
 			feature, BuildContext());
@@ -145,10 +146,10 @@ public async Task HandleElicitationRequest_RestoredToPreviousStatusOnResolve()
 	}
 
 	[Fact]
-	public async Task HandleElicitationRequest_RestoredToIdleWhenNoStatusHistory()
+	public async Task HandleElicitationRequest_RestoredToIdleRunState()
 	{
 		(ElicitationFeature feature, SessionModel session, _) = CreateFeature();
-		// session starts Idle, no history pushed yet
+		// Session starts with an Idle lifecycle state.
 
 		(Task<ElicitationResult> handleTask, ElicitationRequestModel model) = await StartHandleAsync(
 			feature, BuildContext());
@@ -167,12 +168,12 @@ public async Task HandleElicitationRequest_PendingRequestAddedAndRemovedFromSess
 		(Task<ElicitationResult> handleTask, ElicitationRequestModel model) = await StartHandleAsync(
 			feature, BuildContext());
 
-		session.PendingElicitationRequests.ContainsKey(model.Id).ShouldBeTrue();
+		session.PendingInteractions.Elicitations.ContainsKey(model.Id).ShouldBeTrue();
 
 		feature.ResolveElicitationRequest(model.Id, null);
 		await handleTask.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
 
-		session.PendingElicitationRequests.ContainsKey(model.Id).ShouldBeFalse();
+		session.PendingInteractions.Elicitations.ContainsKey(model.Id).ShouldBeFalse();
 	}
 
 	[Fact]
@@ -202,16 +203,16 @@ public async Task HandleElicitationRequest_OnElicitationRequestedFiredWithCorrec
 	}
 
 	[Fact]
-	public async Task HandleElicitationRequest_SecondConcurrentRequestDoesNotPushStatusHistoryAgain()
+	public async Task HandleElicitationRequest_ConcurrentRequestsPreserveRunState()
 	{
 		(ElicitationFeature feature, SessionModel session, _) = CreateFeature();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 
 		(Task<ElicitationResult> task1, ElicitationRequestModel model1) = await StartHandleAsync(feature, BuildContext(message: "First"));
 		(Task<ElicitationResult> task2, ElicitationRequestModel model2) = await StartHandleAsync(feature, BuildContext(message: "Second"));
 
-		// Both pending — only one entry pushed to history (for the Running → NeedsElicitation transition)
-		session.StatusHistory.Count.ShouldBe(1);
+		// Pending interactions do not overwrite the Running lifecycle state.
+		session.AgentRunState.ShouldBe(AgentRunStateEnum.Running);
 		session.Status.ShouldBe(SessionStatusEnum.NeedsElicitation);
 
 		feature.ResolveElicitationRequest(model1.Id, null);
@@ -225,18 +226,21 @@ public async Task HandleElicitationRequest_SecondConcurrentRequestDoesNotPushSta
 
 		// All resolved — restored to Running
 		session.Status.ShouldBe(SessionStatusEnum.Running);
+		session.AgentRunState.ShouldBe(AgentRunStateEnum.Running);
 	}
 
 	// ── Priority resolution ───────────────────────────────────────────────────
 
 	[Fact]
 	public async Task OnElicitationResolve_NeedsPermissionPrioritisedOverElicitation()
 	{
-		(ElicitationFeature feature, SessionModel session, _) = CreateFeature();
+		(ElicitationFeature feature, SessionModel session, TestSessionStateProvider stateProvider) = CreateFeature();
 
 		// Simulate a pending permission request already on the session
-		session.PendingPermissionRequests["perm-1"] = new PermissionRequestModel
+		SessionInteractionCoordinator interactionCoordinator = new(stateProvider);
+		interactionCoordinator.AddPermission(sessionId, new PermissionRequestModel
 		{
+			Id = "perm-1",
 			SessionId = sessionId,
 			FullCommand = "ls",
 			Commands = ["ls"],
@@ -245,7 +249,7 @@ public async Task OnElicitationResolve_NeedsPermissionPrioritisedOverElicitation
 			CanApproveGlobally = true,
 			CanApproveForSession = true,
 			FullRequestJson = "{}"
-		};
+		});
 
 		(Task<ElicitationResult> handleTask, ElicitationRequestModel model) = await StartHandleAsync(
 			feature, BuildContext());
@@ -260,17 +264,19 @@ public async Task OnElicitationResolve_NeedsPermissionPrioritisedOverElicitation
 	[Fact]
 	public async Task OnElicitationResolve_NeedsUserInputPrioritisedOverElicitation()
 	{
-		(ElicitationFeature feature, SessionModel session, _) = CreateFeature();
+		(ElicitationFeature feature, SessionModel session, TestSessionStateProvider stateProvider) = CreateFeature();
 
 		// Simulate a pending user-input request already on the session
-		session.PendingUserInputRequests["ui-1"] = new UserInputRequestModel
+		SessionInteractionCoordinator interactionCoordinator = new(stateProvider);
+		interactionCoordinator.AddUserInput(sessionId, new UserInputRequestModel
 		{
+			Id = "ui-1",
 			SessionId = sessionId,
 			Question = "Continue?",
 			Choices = [],
 			AllowsTextInput = true,
 			FullRequestJson = "{}"
-		};
+		});
 
 		(Task<ElicitationResult> handleTask, ElicitationRequestModel model) = await StartHandleAsync(
 			feature, BuildContext());

Tests/Cockpit.UnitTests/Features/Models/ModelFeatureTests.cs

@@ -64,7 +64,7 @@ public StubByokFeature(params ByokModelConfig[] configs)
 	{
 		Id = Guid.NewGuid().ToString(),
 		Title = "Test",
-		Status = SessionStatusEnum.Idle,
+		AgentRunState = AgentRunStateEnum.Idle,
 		CreatedAt = DateTime.UtcNow,
 		LastActivity = DateTime.UtcNow,
 		Model = MakeModel("default"),

Tests/Cockpit.UnitTests/Features/Permissions/PermissionFeatureTests.cs

@@ -708,7 +708,7 @@ public async Task ConcurrentPermissionChecks_NoRaceConditions()
 	public async Task ResolvePermissionRequest_SessionScope_DoesNotResetStatusToIdle_WhenMultipleRequestsHaveSameCommands()
 	{
 		// Regression test: approving request A with Session scope must not cause status to revert to Idle.
-		// Previously AutoResolveMatchingRequests included A itself, double-popping StatusHistory and landing on Idle.
+		// Previously AutoResolveMatchingRequests included A itself and resolved the same request twice.
 		string testFile = Path.Combine(Path.GetTempPath(), $"test-{Guid.NewGuid()}.json");
 		GlobalPermissionFeature globalFeature = new(NullLogger<GlobalPermissionFeature>.Instance, testFile);
 		TestSessionStateProvider stateProvider = new();
@@ -725,7 +725,7 @@ public async Task ResolvePermissionRequest_SessionScope_DoesNotResetStatusToIdle
 			CreatedAt = DateTime.UtcNow,
 			LastActivity = DateTime.UtcNow,
 			Model = testModel,
-			Status = SessionStatusEnum.Running,
+			AgentRunState = AgentRunStateEnum.Running,
 			Context = new()
 			{
 				CurrentWorkingDirectory = "",
@@ -865,7 +865,7 @@ public async Task CancelPendingRequestsForSession_CancelsAllPending()
 			CreatedAt = DateTime.UtcNow,
 			LastActivity = DateTime.UtcNow,
 			Model = testModel,
-			Status = SessionStatusEnum.Running,
+			AgentRunState = AgentRunStateEnum.Running,
 			Context = new()
 			{
 				CurrentWorkingDirectory = "",
@@ -960,7 +960,7 @@ public async Task ResolvePermissionRequest_GlobalApproval_BlockedByDenyList_Down
 			CreatedAt = DateTime.UtcNow,
 			LastActivity = DateTime.UtcNow,
 			Model = testModel,
-			Status = SessionStatusEnum.Running,
+			AgentRunState = AgentRunStateEnum.Running,
 			Context = new()
 			{
 				CurrentWorkingDirectory = "",
@@ -1026,7 +1026,7 @@ public async Task ResolvePermissionRequest_GlobalApprovalBlockedByDenyList_DoesN
 			CreatedAt = DateTime.UtcNow,
 			LastActivity = DateTime.UtcNow,
 			Model = testModel,
-			Status = SessionStatusEnum.Running,
+			AgentRunState = AgentRunStateEnum.Running,
 			Context = new()
 			{
 				CurrentWorkingDirectory = "",

Tests/Cockpit.UnitTests/Features/SessionEvents/Handlers/SessionIdleHandlerTests.cs

@@ -66,7 +66,7 @@ public void Handle_WithNoGroup_SetsIdle()
 	{
 		// Arrange
 		SessionModel session = CreateSession();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 		SessionEventProcessor processor = CreateProcessor();
 
 		// Act

Tests/Cockpit.UnitTests/Features/SessionEvents/Handlers/SessionShutdownHandlerTests.cs

@@ -43,7 +43,7 @@ public void Handle_RoutineShutdown_DoesNotFinalizeActiveGroup()
 		// Arrange — routine == auto-restart; the session continues, so the group must be preserved
 		SessionModel session = CreateSession();
 		SessionEventProcessor processor = CreateProcessor();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 
 		processor.Process(session, new ToolExecutionStartEvent
 		{
@@ -68,7 +68,7 @@ public void Handle_RoutineShutdown_WithNoGroup_DoesNotSetIdle()
 	{
 		// A routine shutdown with no active group must leave session status unchanged
 		SessionModel session = CreateSession();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 		SessionEventProcessor processor = CreateProcessor();
 
 		processor.Process(session, new SessionShutdownEvent
@@ -112,7 +112,7 @@ public void Handle_ErrorShutdown_WithNoActiveGroup_SetsIdle()
 	{
 		// Even without an active working group, a non-routine shutdown must transition to Idle
 		SessionModel session = CreateSession();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 		SessionEventProcessor processor = CreateProcessor();
 
 		processor.Process(session, new SessionShutdownEvent

Tests/Cockpit.UnitTests/Features/SessionEvents/SessionEventProcessorTests.cs

@@ -192,7 +192,7 @@ public void Process_SessionIdle_WithPendingMessages_FinalizesAndKeepsRunning()
 		// Arrange: enqueue mode — group should be finalized but session stays Running
 		SessionModel session = CreateSession();
 		SessionEventProcessor processor = CreateProcessor();
-		session.Status = SessionStatusEnum.Running;
+		session.AgentRunState = AgentRunStateEnum.Running;
 		session.Messages.Add(new ChatMessageModel { Id = "user1", IsUser = true, Content = "Hello", EventJson = null });
 		session.Messages.Add(new ChatMessageModel { Id = "user2", IsUser = true, Content = "Queued", IsPending = true, EventJson = null });
 		session.ActiveWorkingGroup = new ActivityGroupModel

Tests/Cockpit.UnitTests/Features/Sessions/SessionConversationStateTests.cs

@@ -0,0 +1,119 @@
+using System.Collections.Immutable;
+using Cockpit.Features.SessionEvents.Models;
+using Cockpit.Features.Sessions.Models;
+using GitHub.Copilot;
+using Shouldly;
+
+namespace Cockpit.UnitTests.Features.Sessions;
+
+public sealed class SessionConversationStateTests
+{
+	static SessionModel CreateSession() => new()
+	{
+		Id = "conversation-session",
+		Title = "Conversation state",
+		CreatedAt = DateTime.UtcNow,
+		LastActivity = DateTime.UtcNow,
+		Model = new ModelInfo { Id = "test", Name = "Test Model" },
+		Context = new()
+		{
+			CurrentWorkingDirectory = string.Empty,
+			WorkspacePath = null,
+			GitRoot = null,
+			Repository = null,
+			Branch = null
+		}
+	};
+
+	[Fact]
+	public void ReplacingMessages_PublishesSnapshotThroughConversationState()
+	{
+		SessionModel session = CreateSession();
+		ChatMessageModel message = new() { Id = "message", Content = "Hello", EventJson = null };
+
+		session.Conversation.ReplaceMessages([message]);
+
+		session.Conversation.Messages.ShouldBeSameAs(session.Messages);
+		session.Conversation.MessagesSnapshot.ShouldBe([message]);
+		session.MessagesSnapshot.ShouldBe([message]);
+	}
+
+	[Fact]
+	public void PublishedSnapshot_RemainsStableUntilNextExplicitPublication()
+	{
+		SessionModel session = CreateSession();
+		ChatMessageModel first = new() { Id = "first", Content = "First", EventJson = null };
+		ChatMessageModel second = new() { Id = "second", Content = "Second", EventJson = null };
+		session.Conversation.ReplaceMessages([first]);
+		ImmutableArray<ChatMessageModel> firstSnapshot = session.Conversation.MessagesSnapshot;
+
+		session.Conversation.Messages.Add(second);
+
+		firstSnapshot.ShouldBe([first]);
+		session.Conversation.MessagesSnapshot.ShouldBe([first]);
+
+		session.Conversation.PublishMessagesSnapshot();
+
+		firstSnapshot.ShouldBe([first]);
+		session.Conversation.MessagesSnapshot.ShouldBe([first, second]);
+	}
+
+	[Fact]
+	public void ReplacingMessages_DoesNotRetainCallersMutableCollection()
+	{
+		SessionModel session = CreateSession();
+		ChatMessageModel message = new() { Id = "message", Content = "Hello", EventJson = null };
+		List<ChatMessageModel> source = [message];
+
+		session.Conversation.ReplaceMessages(source);
+		source.Clear();
+
+		session.Conversation.Messages.ShouldBe([message]);
+		session.Conversation.MessagesSnapshot.ShouldBe([message]);
+	}
+
+	[Fact]
+	public void ClearMessages_ReleasesRetainedListCapacity()
+	{
+		SessionModel session = CreateSession();
+		for(int i = 0; i < 256; i++)
+		{
+			session.Conversation.Messages.Add(new ChatMessageModel
+			{
+				Id = $"message-{i}",
+				Content = "Message",
+				EventJson = null
+			});
+		}
+		session.Conversation.PublishMessagesSnapshot();
+		session.Conversation.Messages.Capacity.ShouldBeGreaterThan(0);
+
+		session.Conversation.ClearMessages();
+
+		session.Conversation.Messages.ShouldBeEmpty();
+		session.Conversation.Messages.Capacity.ShouldBe(0);
+		session.Conversation.MessagesSnapshot.ShouldBeEmpty();
+	}
+
+	[Fact]
+	public void CompatibilitySurface_ForwardsToSingleConversationState()
+	{
+		SessionModel session = CreateSession();
+		ActivityGroupModel group = new();
+
+		session.ActiveWorkingGroup = group;
+		session.PendingMessageCount = 2;
+		session.IsCompacting = true;
+		session.AgentTurnCompleted = true;
+		session.HasQueuedImmediateMessage = true;
+		session.PendingTaskSummary = "Complete";
+
+		session.Conversation.ActiveWorkingGroup.ShouldBeSameAs(group);
+		session.Conversation.PendingMessageCount.ShouldBe(2);
+		session.Conversation.IsCompacting.ShouldBeTrue();
+		session.Conversation.AgentTurnCompleted.ShouldBeTrue();
+		session.Conversation.HasQueuedImmediateMessage.ShouldBeTrue();
+		session.Conversation.PendingTaskSummary.ShouldBe("Complete");
+		(session.SessionEventLock == session.Conversation.SyncRoot).ShouldBeTrue();
+	}
+}