[menu] Allow onKeyDown handlers to be called at Group level during typeahead

[atomiks]

• I have followed (at least) the PR section of the contributing guide.

Listeners that execute on keydown around Group level should allow to be called and not be blocked by typeahead, as in Radix.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@3889
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@3889
  

commit: 8a8e8f6

[mui-bot]

Bundle size report

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+293B(+0.07%)	🔺+72B(+0.05%)

Details of bundle changes

---

Check out the code infra dashboard for more information about this PR.

[netlify]

✅ Deploy Preview for base-ui ready!

Name	Link
🔨 Latest commit	8a8e8f6
🔍 Latest deploy log	https://app.netlify.com/projects/base-ui/deploys/697c1c0ebb39eb00086acca8
😎 Deploy Preview	https://deploy-preview-3889--base-ui.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[greptile-apps]

Greptile Overview

Greptile Summary

This PR enables onKeyDown handlers at the Menu.Group level to receive typeahead events while preventing parent menus from re-processing them.

Key changes:

• Introduced a WeakSet-based tracking mechanism to mark typeahead events as handled without mutating them
• Added stopPropagation parameter to useTypeahead (defaults to true for backward compatibility)
• Configured nested menus to allow event bubbling (stopPropagation: false) while stopping propagation at the root level
• Added comprehensive tests validating Group handlers receive events and propagation stops at menu root

Implementation approach:
The solution uses a module-level WeakSet<Event> to track which native events have been processed by typeahead. When an event bubbles up to parent menus, they check if it's already been handled and skip typeahead processing. The stopPropagation flag is set to false for nested menus (parent.type === 'menu' || parent.type === 'nested-context-menu') allowing events to bubble through the menu tree, but remains true at the root to prevent events from escaping to higher-level listeners.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The implementation is well-designed with a clean WeakSet-based approach for event tracking, comprehensive tests validate the behavior, and the changes are backward compatible (stopPropagation defaults to true)
• No files require special attention

Important Files Changed

Filename	Overview
packages/react/src/floating-ui-react/hooks/useTypeahead.ts	Replaced stopEvent with handleTypeaheadEvent to enable conditional event propagation via WeakSet tracking
packages/react/src/menu/root/MenuRoot.tsx	Added stopPropagation: false for nested menus to allow event bubbling through menu tree
packages/react/src/menu/group/MenuGroup.test.tsx	Added tests verifying Group handlers receive typeahead events and events don't bubble above menu root