fix(worker): start_list_handler ehrlich machen, wenn keine App verbunden ist

ConnectedClientTracker zaehlt verbundene UI-Clients (WorkerHub.OnConnectedAsync/
OnDisconnectedAsync). StartListHandler prueft ihn vor dem Broadcast und liefert
bei 0 verbundenen Clients Requested=false plus Reason statt unbedingtem true.
Tool-Beschreibung und external-mcp.md an das reale Verhalten angepasst.

docs/explore-notes/external-mcp.md

@@ -98,6 +98,7 @@ Daily prep: `GetDailyPrepCandidates`, `SetMyDay`.
 | `TaskWaitMcpTools` | `WaitForTaskChange` |
 | `QueueStateMcpTools` | `GetQueueState` |
 | `AttachmentMcpTools` | `AddTaskAttachment`, `ListTaskAttachments`, `RemoveTaskAttachment` |
+| `ListHandlerMcpTools` | `StartListHandler` |
 
 ## Per-tool behaviour worth knowing
 
@@ -235,6 +236,13 @@ task already outside those two (unknown ids reported as status `"NotFound"`, als
 **`AttachmentMcpTools`** — re-attaching the same `fileName` overwrites. Add/remove refuse on a
 `Running` task.
 
+**`StartListHandler`** — the worker only broadcasts `ListHandlerStartRequested`; the connected
+ClaudeDo App does the actual work (creates the handler task, opens the triage ConPTY tile). Before
+broadcasting it checks `ConnectedClientTracker` (a `WorkerHub.OnConnectedAsync`/`OnDisconnectedAsync`-driven
+singleton count) — with zero connected clients the broadcast would reach nobody, so the tool
+returns `Requested: false` plus a `Reason` instead of claiming success. Does not queue or retry the
+request for a later connect.
+
 **`GetDailyPrepCandidates`** — Idle, non-blocked tasks in a git repo **not** excluded by
 `AppSettings.ReportExcludedPaths` and not already `IsMyDay`, plus the current Idle MyDay tasks
 and `maxTasks` (= `DailyPrepMaxTasks`). Repo-exclusion logic lives in the `DailyPrepFilter`