What is equivalent to `InteractiveShell.kernel.comm_manager.register_target('file_request', target_func)`?

Hi,
I encountered this error while using an [interactive tool](https://github.com/igvteam/igv-notebook/blob/b81c898f726bebad1306a1dc09d4009e23c68417/igv_notebook/file_reader.py#L61C60-L61C72) through CaptureShell:
```
---> 61 get_ipython().kernel.comm_manager.register_target('file_request', target_func)
AttributeError: 'CaptureShell' object has no attribute 'kernel'
```
Is there any equivalent to InteractiveShell's `InteractiveShell.kernel.comm_manager.register_target('file_request', target_func)` or colab notebook's `google.colab.output.register_callback('ReadFile', callback)` attributes that I could use to resolve the error?
Thanks.

Start with igv_notebook/file_reader.py at line 61 and trace how CaptureShell handles the call to register_target. Compare the available CaptureShell execution path with InteractiveShell and the linked Colab callback behavior. Done means the supported equivalent or limitation is identified and the file_request flow no longer depends on a missing kernel attribute.

Written by the indexing model from the issue text.