Debug toolbar causes crashes viewing course in devstack

On some pages, the lms or cms crashes with a traceback involving the debug_toolbar and a type error:

Traceback (most recent call last):
  File "/openedx/venv/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/middleware.py", line 145, in __call__
    return self._postprocess(request, response, toolbar)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/middleware.py", line 182, in _postprocess
    panel.generate_stats(request, response)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/panels/cache.py", line 212, in generate_stats
    self.record_stats(
    ^
  File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/panels/__init__.py", line 194, in record_stats
    self.toolbar.store.save_panel(
    ^
  File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/store.py", line 122, in save_panel
    cls._request_store[request_id][panel_id] = serialize(data)
                                               ^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/store.py", line 32, in serialize
    return json.dumps(data, cls=DebugToolbarJSONEncoder)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/pyenv/versions/3.11.8/lib/python3.11/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
          ^^^^^^^^^^^
  File "/opt/pyenv/versions/3.11.8/lib/python3.11/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/pyenv/versions/3.11.8/lib/python3.11/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^

Exception Type: TypeError at /courses/course-v1:OpenedX+DemoX+DemoCourse/about
Exception Value: keys must be str, int, float, bool or None, not tuple

To reproduce:

1. Deploy a Tutor dev master devstack, with current master branch of edx-platform bind-mounted:

# with tutor at git master
tutor config save
tutor mounts add ./edx-platform
tutor images build openedx-dev
tutor dev launch

2. Create a user and import the demo course:

tutor dev do createuser --staff --superuser samuel samuel@example.com --password password
tutor dev do importdemocourse

3. Log in as that user. You should be redirected to http://apps.local.openedx.io:1996/learner-dashboard/
4. Click "Explore courses". This should take you to http://local.openedx.io:8000/courses
5. Find the "Open edX Demo Course" and click "Learn More"
6. Observe the debug crash page.

The page doesn't always crash. It most commonly crashes in the first few loads, then after that it consistently succeeds.

I also observe this on other requests relating to the demo course.
For example, clicking the "View this course as: " can fail,
and in the network requests you will see a 500 error from the request to http://local.openedx.io:8000/courses/course-v1:OpenedX+DemoX+DemoCourse/masquerade .
The logs will show a similar traceback:

lms-1          | 2025-08-01 01:13:35,253 ERROR 54 [django.request] [user 4] [ip 172.18.0.1] log.py:246 - Internal Server Error: /courses/course-v1:OpenedX+DemoX+DemoCourse/masquerade
lms-1          | Traceback (most recent call last):
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
lms-1          |     response = get_response(request)
lms-1          |                ^^^^^^^^^^^^^^^^^^^^^
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/middleware.py", line 145, in __call__
lms-1          |     return self._postprocess(request, response, toolbar)
lms-1          |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/middleware.py", line 182, in _postprocess
lms-1          |     panel.generate_stats(request, response)
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/panels/request.py", line 63, in generate_stats
lms-1          |     self.record_stats({"session": sanitize_and_sort_request_vars(session_data)})
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/panels/__init__.py", line 194, in record_stats
lms-1          |     self.toolbar.store.save_panel(
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/store.py", line 122, in save_panel
lms-1          |     cls._request_store[request_id][panel_id] = serialize(data)
lms-1          |                                                ^^^^^^^^^^^^^^^
lms-1          |   File "/openedx/venv/lib/python3.11/site-packages/debug_toolbar/store.py", line 32, in serialize
lms-1          |     return json.dumps(data, cls=DebugToolbarJSONEncoder)
lms-1          |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-1          |   File "/opt/pyenv/versions/3.11.8/lib/python3.11/json/__init__.py", line 238, in dumps
lms-1          |     **kw).encode(obj)
lms-1          |           ^^^^^^^^^^^
lms-1          |   File "/opt/pyenv/versions/3.11.8/lib/python3.11/json/encoder.py", line 200, in encode
lms-1          |     chunks = self.iterencode(o, _one_shot=True)
lms-1          |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lms-1          |   File "/opt/pyenv/versions/3.11.8/lib/python3.11/json/encoder.py", line 258, in iterencode
lms-1          |     return _iterencode(o, 0)
lms-1          |            ^^^^^^^^^^^^^^^^^
lms-1          | TypeError: keys must be str, int, float, bool or None, not CourseLocator

Removing the DEBUG TOOLBAR section from cms/envs/devstack.py and lms/envs/devstack.py appears to fix the problem,
but I'm unsure if it's a problem in the debug toolbar,
or if there is data in an incorrect type.

Start with cms/envs/devstack.py and lms/envs/devstack.py, then inspect the debug_toolbar traceback and the failing course-page requests using the provided Tutor devstack reproduction steps. Determine whether the toolbar or the request data produces unsupported dictionary keys; done means the debug toolbar remains enabled and course, masquerade, and related requests no longer return 500 errors.