What problem are you trying to solve with Submitty
Notebook Builder currently does not expose support for file_submission notebook cells, even though Submitty’s notebook runtime already supports them. This means instructors can create some notebook cell types through the Builder UI, but still need to manually edit config.json when they want to add file upload areas inside a notebook gradeable. That makes Notebook Builder less useful as a guided authoring tool for basic and moderate notebook-based assignment workflows.

Describe the way you'd like to solve this problem
I would like Notebook Builder to support file_submission cells through a guided UI, similar to the existing support for Markdown, Multiple Choice, Short Answer, Image, and Item cells. Ideally, instructors should be able to add a file_submission notebook cell directly in the Builder and configure fields such as:

• label
• directory

This would allow instructors to create and edit notebook file upload areas without manually writing raw JSON.

Describe any potential alternatives you'd tried to solve the problem
The current workaround is to manually edit config.json or use the raw configuration editor instead of the Builder. While that works, it defeats the purpose of having Notebook Builder as a structured and beginner-friendly authoring interface.

Additional context
I confirmed this behavior in the running instructor UI. In Notebook Builder, the available notebook cell types currently include:

• Markdown
• Multiple Choice
• Short Answer
• Image
• Item
• Itempool Item

There is no File Submission option in the Builder UI.

At the same time, Submitty’s runtime already supports file_submission cells, for example:

• site/app/templates/notebook/Notebook.twig
• more_autograding_examples/notebook_filesubmission/config/config.json

So this appears to be a builder-to-runtime gap: the notebook runtime supports file_submission, but Notebook Builder does not currently expose it.