There's a lot discussion here on whether the carret is important enough to justify indenting the screen to use precious screen space.

Rather than a carret, could I propose the notebook icon is instead toggled to display the state of the list - similar would be done for the tags.

  • This would ensure no additional screen space is occupied unnecessarily, but still give us visual indication on the state of the sidebar.

Example

Open book icon to indicate the sidebar is expanded