Sidebar Disappears in a Hypothesis Assignment in Canvas that Uses a Specific URL

Copied from: https://github.com/hypothesis/support/issues/200

## Bug report form
### Steps to reproduce
1. In Canvas, create an assignment that uses the URL `https://www.gcu.edu/blog/teaching-school-administration/why-growth-mindset-important-in-classroom`. See sample assignment: https://hypothesis.instructure.com/courses/739/assignments/9045. Use `eng+canvasteacher@hypothes.is`.
2. Configure the assignment not to load in a new tab.
3. Launch the assignment.
4. Configure the assignment to load in a new tab.
5. Open the assignment and have a student annotate it.
6. Using an instructor account, launch SpeedGrader.

https://github.com/user-attachments/assets/656a193b-69d3-4117-8ca5-a2001808379e

### Expected behaviour
The webpage and the Hypothesis sidebar displays correctly with all the annotations.

### Actual behaviour
When the assignment is not configured to load in a new tab, the sidebar does not display when the assignment is opened.
When opening the assignment via SpeedGrader, the sidebar does not display. This is whether the assignment is configured to load or not in a new tab.

### Browser/system information
Tell us which browser, browser version, and operating system you were using when
you encountered this issue.

### Additional details
Chrome 137
Mac OS 15.5

Related ticket: https://app.hubspot.com/contacts/6291320/record/0-5/26144351780