chore(claude-do): Mission Control: allgemeiner Session-Handoff an eine frische

## Ziel

Jede Mission-Control-Session (Ad-hoc UND Task-Session) soll ihre Arbeit an eine frische Session
uebergeben koennen: "gib das ab an eine neue Session". Die alte Kachel wird geschlossen, an
derselben Position oeffnet eine frische Session im selben cwd, die mit einem Brief startet, den
die abgebende Session selbst geschrieben hat.

Motivation: eine lange Session mit vollem/verrottetem Kontex

ClaudeDo-Task: 8b846deb-ad10-4243-9272-9aea2a01ec93

src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs

@@ -30,6 +30,10 @@ public interface IWorkerClient : INotifyPropertyChanged
     /// task to carry out nextPhase ("wait" | "merge" | "wait_final" | "merge_final").</summary>
     event Action<string, IReadOnlyList<string>, string>? HandoffRequestedEvent;
 
+    /// <summary>A Mission Control session called handoff_session: (paneId, briefPath). The UI replaces
+    /// the tile whose IdentityKey is paneId with a fresh session starting from the brief.</summary>
+    event Action<string, string>? SessionHandoffRequestedEvent;
+
     /// <summary>start_list_handler was called through the external MCP: (listId, taskIds). The UI
     /// starts a list-handler run for them exactly like the "Let Claude handle it" button.</summary>
     event Action<string, IReadOnlyList<string>>? ListHandlerStartRequestedEvent;
@@ -133,8 +137,10 @@ public interface IWorkerClient : INotifyPropertyChanged
     /// in a task's worktree (same worktree prep as an autonomous run).</summary>
     Task<LaunchSpec> GetInteractiveLaunchSpecAsync(string taskId, CancellationToken ct = default);
     /// <summary>Launch spec for an ad-hoc interactive session in an arbitrary directory --
-    /// no task, no worktree.</summary>
-    Task<LaunchSpec> GetAdHocLaunchSpecAsync(string directory, CancellationToken ct = default);
+    /// no task, no worktree. paneId (the tile's IdentityKey) is rendered into the handoff hint.</summary>
+    Task<LaunchSpec> GetAdHocLaunchSpecAsync(string directory, string paneId, CancellationToken ct = default);
+    /// <summary>Launch spec for the fresh session a tile hands off to after handoff_session.</summary>
+    Task<LaunchSpec> GetSessionHandoffLaunchSpecAsync(string paneId, string cwd, string briefPath, string? taskId, CancellationToken ct = default);
     /// <summary>Launch spec for an embedded ConPTY "merge helper" session that drives the given
     /// tasks to a merged/Done state. listId scopes the session (and cwd) to that list.
     /// handlerTaskId (from CreateMergeHelperTaskAsync) is rendered into the brief so the session

src/ClaudeDo.Ui/Services/WorkerClient.cs

@@ -49,6 +49,7 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public event Action<string, string, string>? TaskQuestionAskedEvent;
     public event Action<string, string>? TaskQuestionResolvedEvent;
     public event Action<string, IReadOnlyList<string>, string>? HandoffRequestedEvent;
+    public event Action<string, string>? SessionHandoffRequestedEvent;
     public event Action<string, IReadOnlyList<string>>? ListHandlerStartRequestedEvent;
     public event Action<string, string>? HandlerUsageWarningEvent;
     public event Action? ConnectionRestoredEvent;
@@ -160,6 +161,11 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
             Dispatcher.UIThread.Post(() => HandoffRequestedEvent?.Invoke(taskId, survivingTaskIds, nextPhase));
         });
 
+        _hub.On<string, string>("SessionHandoffRequested", (paneId, briefPath) =>
+        {
+            Dispatcher.UIThread.Post(() => SessionHandoffRequestedEvent?.Invoke(paneId, briefPath));
+        });
+
         _hub.On<string, IReadOnlyList<string>>("ListHandlerStartRequested", (listId, taskIds) =>
         {
             Dispatcher.UIThread.Post(() => ListHandlerStartRequestedEvent?.Invoke(listId, taskIds));
@@ -620,8 +626,11 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public async Task<LaunchSpec> GetInteractiveLaunchSpecAsync(string taskId, CancellationToken ct = default)
         => await InvokeTimedAsync<LaunchSpec>("GetInteractiveLaunchSpec", () => _hub.InvokeAsync<LaunchSpec>("GetInteractiveLaunchSpec", taskId, ct));
 
-    public async Task<LaunchSpec> GetAdHocLaunchSpecAsync(string directory, CancellationToken ct = default)
-        => await InvokeTimedAsync<LaunchSpec>("GetAdHocLaunchSpec", () => _hub.InvokeAsync<LaunchSpec>("GetAdHocLaunchSpec", directory, ct));
+    public async Task<LaunchSpec> GetAdHocLaunchSpecAsync(string directory, string paneId, CancellationToken ct = default)
+        => await InvokeTimedAsync<LaunchSpec>("GetAdHocLaunchSpec", () => _hub.InvokeAsync<LaunchSpec>("GetAdHocLaunchSpec", directory, paneId, ct));
+
+    public async Task<LaunchSpec> GetSessionHandoffLaunchSpecAsync(string paneId, string cwd, string briefPath, string? taskId, CancellationToken ct = default)
+        => await InvokeTimedAsync<LaunchSpec>("GetSessionHandoffLaunchSpec", () => _hub.InvokeAsync<LaunchSpec>("GetSessionHandoffLaunchSpec", paneId, cwd, briefPath, taskId, ct));
 
     public async Task<LaunchSpec> GetMergeHelperLaunchSpecAsync(IReadOnlyList<string> taskIds, string listId, string handlerTaskId, string? model = null, CancellationToken ct = default)
         => await InvokeTimedAsync<LaunchSpec>("GetMergeHelperLaunchSpec", () => _hub.InvokeAsync<LaunchSpec>("GetMergeHelperLaunchSpec", taskIds, listId, handlerTaskId, model, ct));