ui/layout: expand collapsed vertical tabs on hover

[dusan-nikcevic]

• An issue exists where the maintainers agreed that this should be implemented
• I tested that my contribution works locally, and does not break anything
• If my contribution is non-trivial, I did not use AI to write most of it
• I understand that I will be permanently banned from interacting with this organization if I lied by checking any of these checkboxes.

Tested on (check one or more):

• Linux
• Windows
• macOS

---

Closes #915.

This adds an optional hover-expand mode for collapsed vertical tabs.

What changed:

• add a setting to expand collapsed vertical tabs on hover
• expand the collapsed vertical tab strip as an overlay instead of relaying out page content
• keep hover expansion/collapse behavior reliable with delay handling
• avoid hover-triggered expansion while interaction locks are active

Local verification:

• built Helium locally on Linux
• launched the built browser
• manually verified the collapsed vertical sidebar expands on hover

2026-02-27.00-12-54.online-video-cutter.com.mp4

[greptile-apps]

_{Last reviewed commit: 82b073c}

[cyfung1031]

This doesn’t seem to involve layout resizing on mouse hover. I hope the maintainers can review this.

[JackDerksen]

This doesn’t seem to involve layout resizing on mouse hover. I hope the maintainers can review this.

You mean resizing the main page layout in accordance to the sidebar expanding? That's visually jarring and more expensive than expanding as an overlay like this. If you want it to resize the page, just toggle the expansion with the button or cmd+s.