feat(ui): interactive chat composer state on the session monitor VM

TaskMonitorViewModel gains IsInteractiveLive + ComposerDraft + SubmitComposer
(optimistic LogKind.User echo, then SendInteractiveMessageAsync) + StopInteractive,
driven by the InteractiveSessionStarted/Ended events. Since DetailsIslandViewModel
embeds this monitor, both task detail and Mission Control get the composer. Mission
Control auto-creates a monitor on InteractiveSessionStarted. Adds LogKind.User.

tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs

@@ -57,6 +57,9 @@ public abstract class StubWorkerClient : IWorkerClient
     public void RaisePrepLine(string line) => PrepLineEvent?.Invoke(line);
     public void RaisePrepFinished(bool ok) => PrepFinishedEvent?.Invoke(ok);
 
+    public void RaiseInteractiveStarted(string taskId) => InteractiveSessionStartedEvent?.Invoke(taskId);
+    public void RaiseInteractiveEnded(string taskId) => InteractiveSessionEndedEvent?.Invoke(taskId);
+
     public virtual bool IsConnected => false;
     public virtual bool IsReconnecting => false;
     public virtual string? LastApproveTarget => null;
@@ -135,8 +138,18 @@ public abstract class StubWorkerClient : IWorkerClient
     public virtual Task SetOnlineInboxConfigAsync(OnlineInboxConfigInputDto input) => Task.CompletedTask;
     public virtual Task SetOnlineInboxAuthAsync(string refreshToken) => Task.CompletedTask;
     public virtual Task ClearOnlineInboxAuthAsync() => Task.CompletedTask;
-    public virtual Task SendInteractiveMessageAsync(string taskId, string text) => Task.CompletedTask;
-    public virtual Task StopInteractiveSessionAsync(string taskId) => Task.CompletedTask;
+    public List<(string TaskId, string Text)> SentInteractive { get; } = new();
+    public virtual Task SendInteractiveMessageAsync(string taskId, string text)
+    {
+        SentInteractive.Add((taskId, text));
+        return Task.CompletedTask;
+    }
+    public List<string> StoppedInteractive { get; } = new();
+    public virtual Task StopInteractiveSessionAsync(string taskId)
+    {
+        StoppedInteractive.Add(taskId);
+        return Task.CompletedTask;
+    }
 
     protected void RaisePropertyChanged(string name) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
 }

tests/ClaudeDo.Ui.Tests/ViewModels/TaskMonitorViewModelTests.cs

@@ -189,4 +189,112 @@ public class TaskMonitorViewModelTests : IDisposable
 
         Assert.False(vm.HasPendingQuestion);
     }
+
+    // ── Interactive composer ──────────────────────────────────────────────────
+
+    [Fact]
+    public void InteractiveStarted_ForSubscribedTask_SetsIsInteractiveLive()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+
+        worker.RaiseInteractiveStarted("t1");
+
+        Assert.True(vm.IsInteractiveLive);
+        Assert.Equal("running", vm.AgentState);
+    }
+
+    [Fact]
+    public void InteractiveStarted_ForOtherTask_IsIgnored()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+
+        worker.RaiseInteractiveStarted("other");
+
+        Assert.False(vm.IsInteractiveLive);
+    }
+
+    [Fact]
+    public void InteractiveEnded_ForSubscribedTask_ClearsIsInteractiveLive()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+        worker.RaiseInteractiveStarted("t1");
+
+        worker.RaiseInteractiveEnded("t1");
+
+        Assert.False(vm.IsInteractiveLive);
+        Assert.Equal("done", vm.AgentState);
+    }
+
+    [Fact]
+    public void InteractiveEnded_ForOtherTask_IsIgnored()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+        worker.RaiseInteractiveStarted("t1");
+
+        worker.RaiseInteractiveEnded("other");
+
+        Assert.True(vm.IsInteractiveLive); // unchanged
+    }
+
+    [Fact]
+    public void SubmitComposerCommand_CanExecute_FalseWhenNotLive()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+        vm.ComposerDraft = "hello";
+
+        Assert.False(vm.SubmitComposerCommand.CanExecute(null));
+    }
+
+    [Fact]
+    public void SubmitComposerCommand_CanExecute_FalseWhenLiveButDraftWhitespace()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+        worker.RaiseInteractiveStarted("t1");
+        vm.ComposerDraft = "   ";
+
+        Assert.False(vm.SubmitComposerCommand.CanExecute(null));
+    }
+
+    [Fact]
+    public void SubmitComposerCommand_CanExecute_TrueWhenLiveAndDraftSet()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+        worker.RaiseInteractiveStarted("t1");
+        vm.ComposerDraft = "hello";
+
+        Assert.True(vm.SubmitComposerCommand.CanExecute(null));
+    }
+
+    [Fact]
+    public async Task SubmitComposer_AddsUserLogLine_ClearsDraft_CallsClient()
+    {
+        var worker = new FakeWorker();
+        using var vm = Build(worker);
+        vm.SetTaskId("t1");
+        worker.RaiseInteractiveStarted("t1");
+        vm.ComposerDraft = "do the thing";
+
+        await vm.SubmitComposerCommand.ExecuteAsync(null);
+
+        Assert.Single(worker.SentInteractive);
+        Assert.Equal(("t1", "do the thing"), worker.SentInteractive[0]);
+        Assert.Equal(string.Empty, vm.ComposerDraft);
+        Assert.Single(vm.Log);
+        Assert.Equal(LogKind.User, vm.Log[0].Kind);
+        Assert.Equal("do the thing", vm.Log[0].Text);
+    }
 }