Crash when executing a cell with an output which does not have a name

[krassowski]

Description

This code assumes that all cell outputs have a name:

jupyter-server-nbmodel/jupyter_server_nbmodel/actions.py

Lines 110 to 112 in b99f3c5

	if (not cell_outputs) or (cell_outputs[-1]["name"] != output["name"]):
	output["text"] = [text]
	cell_outputs.append(output)

Reproduce

1. Create the following cell

import matplotlib.pyplot as plt
plt.figure()
plt.show()
print('test')

2. Attempt to run it
3. See error:

[E 2025-07-18 11:20:18.050 ServerApp.jupyter_server_nb_model] Failed to process execution request 3698140a-5d25-4032-8799-bdf14c19d8bd for kernel e83b630e-ff21-48e2-b57c-210be95502aa.
    Traceback (most recent call last):
      File "/home/jupyter/notebook-env/lib/python3.11/site-packages/jupyter_server_nbmodel/handlers.py", line 324, in _kernel_worker
        results[uid] = await _execute_snippet(
                       ^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/jupyter/notebook-env/lib/python3.11/site-packages/jupyter_server_nbmodel/handlers.py", line 263, in _execute_snippet
        reply = await ensure_async(
                ^^^^^^^^^^^^^^^^^^^
      File "/home/jupyter/notebook-env/lib/python3.11/site-packages/jupyter_core/utils/__init__.py", line 197, in ensure_async
        result = await obj
                 ^^^^^^^^^
      File "/home/jupyter/notebook-env/lib/python3.11/site-packages/jupyter_client/client.py", line 565, in _async_execute_interactive
        output_hook(msg)
      File "/home/jupyter/notebook-env/lib/python3.11/site-packages/jupyter_server_nbmodel/handlers.py", line 156, in _output_hook
        if (not cell_outputs) or (cell_outputs[-1]["name"] != output["name"]):
                                  ~~~~~~~~~~~~~~~~^^^^^^^^
    KeyError: 'name'

Expected behavior

No crash

Context

This code will need a fix regardless of #43.

[krassowski]

Per specification the only guaranteed member of output is output_type. name exists exclusively on stream outputs. If the previous output was not a stream, then the current logic will fail.

Minimal reproducer is thus:

display('test')
print('test')