Fix mention picker tab wrapping

[YUHAO-corn]

Summary

• keep mention picker category tabs on a single row
• allow the tab rail to scroll horizontally instead of wrapping labels
• update the mention popover style coverage for the new no-wrap contract

Fixes #3890.

Surface area

• UI
• Daemon/runtime
• Docs
• Tests only

Tests

• node lightweight CSS assertion for mention tab rules
• git diff --check

Note: the focused Vitest command could not run locally in this fresh worktree because node_modules is not installed; relying on CI for the full test run.

[lefarcen]

Hey @YUHAO-corn! The fix is well-scoped — nowrap + horizontal scroll is exactly the right contract to hold the tab rail stable regardless of how many file-backed tabs appear. The test coverage update mirrors the change cleanly.

One small template gap before this goes to pool review: could you add a ## Surface area section and tick UI (this change affects the mention picker tab rail visually)? The rest of the body reads clearly as-is.

[github-actions]

Visual regression review

Head: a77fed4 · Base: 75f1472

3 changed · 14 unchanged · 0 missing baseline · 0 failed

Changed cases

Case	Main	PR	Diff
visual-design-systems
visual-home-plugin-filter
visual-new-project-modal

Unchanged cases

Case	Main	PR	Diff
visual-avatar-menu
visual-home
visual-home-catalog
visual-home-context-picker
visual-integrations
visual-integrations-use-everywhere
visual-plugin-details
visual-plugins
visual-projects
visual-projects-kanban
visual-settings-byok
visual-settings-execution
visual-tasks
visual-topbar-execution-switcher

Visual diff is advisory only and does not block merging.

[lefarcen]

All gates green — @Siri-Ray approved, CI is passing. Flagged for the maintainers to merge. Thanks for the clean fix @YUHAO-corn! 🎉

[kokisanai]

Hi @YUHAO-corn!

This PR looks quiet for a bit, so I'm checking in to make sure it doesn't get stuck.

If you are waiting on review, feedback, or a specific unblock from the team, feel free to say so here. If faster coordination helps, you can also drop into our contributors channel in Discord:
https://discord.gg/3C6EWXbdQQ

We want to help move this forward instead of letting it stall.

[github-actions]

@YUHAO-corn friendly reminder: this PR has been waiting on an author response for more than 3 days after reviewer or maintainer feedback.

When you have a chance, please reply here or push an update. To keep the queue manageable, PRs with no author activity for more than 5 days after feedback may be closed automatically, but they can be reopened when work resumes.

[lefarcen]

🧪 This PR has changes that need manual QA validation, so it needs a QA pass by @AmyShang-alt before merge — please hold off self-merging; we'll loop QA in once it's merge-ready.

[lefarcen]

Hey @YUHAO-corn — thanks for the focused fix. Since this PR changes visible mention picker UI behavior, could you please add screenshots to the PR body?

The key change is that the mention picker category tabs should stay on a single row and scroll horizontally instead of wrapping onto multiple lines. Without screenshots, it is hard to verify the real UI layout, especially when many file-backed tabs are present.

A small before/after capture would be ideal:

• Before: mention picker tabs wrapping onto two lines
• After: tabs staying on one row with horizontal overflow behavior

This will make the UI review much easier. Thanks! 🙌

[github-actions]

Closing this PR for now because it has been waiting on an author response for more than 5 days after reviewer or maintainer feedback.

This is only a queue-management step, not a rejection of the work. If you would like to continue, please leave a comment or push an update and reopen the PR when ready.