F4: verify task recovery and document Prompt background jobs

frontend/src/components/assistant-editor/background-task-panel.tsx

@@ -45,6 +45,7 @@ function TaskCard({ task, onChanged }: { task: BackgroundTask; onChanged: () =>
       <Button size="sm" disabled={busy || !request.questions?.every((_, index) => answers[index]?.trim())} onClick={() => void act(() => backgroundTasksApi.input(task.id, { answers: request.questions?.map((question, index) => question.multiple ? answers[index].split(/[,，]/).map(value => value.trim()).filter(Boolean) : [answers[index].trim()]) }))}>发送回复</Button>
     </div>}
     {task.result && <details><summary className="cursor-pointer text-muted-foreground">查看结果</summary><pre className="mt-2 max-h-48 overflow-auto whitespace-pre-wrap break-words font-sans">{task.result}</pre></details>}
+    {task.status === "unknown" && <Button size="sm" variant="outline" disabled={busy} onClick={() => void act(() => backgroundTasksApi.refresh(task.id))}>核查远端状态</Button>}
     {!terminal.has(task.status) && <Button size="sm" variant="outline" disabled={busy} onClick={() => void act(() => backgroundTasksApi.cancel(task.id))}>{task.status === "cancel_requested" ? "再次核查停止" : "停止任务"}</Button>}
     {error && <p role="alert" className="text-destructive">{error}</p>}
   </article>;

frontend/src/components/tools/tool-binding-editor.tsx

@@ -556,9 +556,10 @@ export function ToolBindingEditor({
     () => tools.filter((tool) => tool.status === "active"),
     [tools],
   );
+  const selectedTaskId = value.find(binding => tools.find(tool => tool.id === binding.toolId)?.type === "task")?.toolId;
   const pickerTools = useMemo(
-    () => (selectableTools ?? tools).filter((tool) => tool.status === "active" && (allowTask || tool.type !== "task")),
-    [selectableTools, tools, allowTask],
+    () => (selectableTools ?? tools).filter((tool) => tool.status === "active" && (allowTask || tool.type !== "task") && (tool.type !== "task" || !selectedTaskId || tool.id === selectedTaskId)),
+    [selectableTools, tools, allowTask, selectedTaskId],
   );
   const selectedIds = new Set(value.map((binding) => binding.toolId));
   const variableNames = [...Object.keys(variables), ...SYSTEM_VARIABLE_NAMES];

frontend/src/lib/api.ts

@@ -1004,6 +1004,7 @@ export type BackgroundTask = {
   };
 };
 export const backgroundTasksApi = {
+  refresh: (id: string) => request<BackgroundTask>(`/api/background-tasks/${encodeURIComponent(id)}/refresh`, { method: "POST" }),
   list: (assistantId: string) => request<BackgroundTask[]>(`/api/background-tasks?assistant_id=${encodeURIComponent(assistantId)}`),
   cancel: (id: string) => request<BackgroundTask>(`/api/background-tasks/${encodeURIComponent(id)}/cancel`, { method: "POST" }),
   input: (id: string, value: { reply?: string; answers?: string[][] }) => request<BackgroundTask>(`/api/background-tasks/${encodeURIComponent(id)}/input`, { method: "POST", body: JSON.stringify(value) }),