Found a bug? Please fill out the sections below. 👍

Issue Summary

In a project with two template engines, the same pattern templates are picked twice and show up duplicated on the menu.

Steps to Reproduce

1. Set up Jinja and Django as template engines so that both of them load the pattern library templates.
2. Each pattern will show up twice on the menu

You can see this on the Firefox site codebase:

https://github.com/mozmeao/springfield/blob/c8a674bc4dea18a51485dae4f77e9a46bfe80b5a/springfield/settings/base.py#L787

Docs: https://mozmeao.github.io/platform-docs/install/

Any other relevant information. For example, why do you consider this a bug and what did you expect to happen instead?

The fix is implemented here: main...lincolnloop:django-pattern-library:remove-duplicates

Technical details

• Python version: 3.13.9
• Django version: 5.2.7
• Browser version: irrelevant