F2: persist native job projections and expose task controls

backend/routes/assistants.py

@@ -242,6 +242,11 @@ async def _validate_tool_bindings(
     missing = sorted(tool_ids - set(tools))
     if missing:
         raise HTTPException(400, "工具不存在或未启用: " + ", ".join(missing))
+    task_tools = [tool for tool in tools.values() if tool.type == "task"]
+    if task_tools and (body.type != "prompt" or body.runtime_mode != "pipeline"):
+        raise HTTPException(400, "后台任务工具仅支持提示词 Pipeline")
+    if len(task_tools) > 1:
+        raise HTTPException(400, "每个助手最多绑定一个后台任务工具")
     reserved = sorted(
         tool.function_name
         for tool in tools.values()
@@ -282,6 +287,8 @@ async def _validate_tool_bindings(
             type=tool.type,
             definition=tool.definition or {},
         )
+        if tool.type == "task" and binding.result_assignments:
+            raise HTTPException(400, "后台任务结果通过任务通知返回，不支持结果变量映射")
         properties, required = ToolExecutor.input_schema(runtime_tool)
         unknown = sorted(set(binding.argument_bindings) - set(properties))
         if unknown: