## User Story
"As an editor, I frequently use the tools provided in the sidebar and would like it to remain open and available as I navigate the site".
As discussed in T246427, the collapsible sidebar should have the ability to maintain its collapsed/expanded state while navigating between pages. This task encompasses the work needed to implement that functionality **for logged-in users only**. The state will be tied to the users account, and will therefore persist across devices and loggged-in sessions as well.
## Technical approach
A new user-preference that stores the sidebar open/collapsed state needs to be created. Based on that preference, we conditionally set the `checked` attribute of the `<input type="checkbox" class="vector-menu-checkbox vectorMenuCheckbox" aria-labelledby="{{label-id}}" />` element in [[ https://github.com/wikimedia/Vector/blob/72afb66fb8b3f571b1deba131e53f03447a4df2d/includes/templates/Menu.mustache#L9 | Menu.mustache ]].
The user preference should not be visible as an option in Special:Preferences, since it would be redundant to have the same functionality in two places.
## Open questions
- **How do we handle mobile?** Does the sidebar remain open on mobile devices? do we override the user-preference at a certain breakpoint?** [[design needed]]**
## Acceptance criteria
- Sidebar retains state:
- [] while navigating between pages.
- [] across devices.
- [] after logging-out and logging back in again.