Side menu "Add block" (+) not usable with keyboard (hover-only, Tab captured, Enter/Space) #2576

What’s broken?

Problem

The “Add block” (+) button in the left margin:

• Mostly appears on mouse hover : little or no access with keyboard only.
• Tab rarely reaches it: the editor captures Tab for indenting blocks, with no exception for the side menu
• Enter / Space often don’t open the insert menu when the handler is on the icon instead of the actual button.

What did you expect to happen?

The + button should appear and be reachable without mouse hover, Tab should focus it when the side menu is visible, and Enter/Space should open the insert menu like a click, including with a screen reader.

Steps to reproduce

1. Open a document without hovering the margin.
2. Move the caret with the keyboard : the + is often missing.
3. If it appears (e.g. after hover), press Tab : focus often goes on and then disapears
4. If focus is on +, Enter or Space : insert menu doesn’t always open.

BlockNote version

No response

Environment

No response

Additional context

1. Show the side menu when the caret / selection is in a block (not only on mousemove), and don’t hide it on Tab / arrow keys.
2. Don’t capture Tab for nesting while the side menu is shown
3. Attach onClick to SideMenu.Button, not only the inner icon.

Contribution

• I'd be interested in contributing a fix for this issue

Sponsor

• I'm a sponsor and would appreciate if you could look into this sooner than later 💖