[navigation menu] Preserve exit transition when controlled

[mattrothenberg]

Problem

When NavigationMenu is controlled, consumers can close it by updating value to null directly. That prop-driven close does not go through the same internal setValue(null, eventDetails) path used by interactions like hover-out, so the popup dimensions may be measured after active content has already started unmounting. In that case the popup can collapse immediately, making the data-ending-style exit transition appear to be skipped.

Reproduction

Working

https://stackblitz.com/edit/vitejs-vite-czwevbev?file=src%2FApp.tsx

Solution

• snapshot the current popup and positioner dimensions when an open controlled NavigationMenu commits to closing
• reuse the existing fixed-size CSS variables used by the internal interaction close path
• keep the change internal to NavigationMenu without adding a new public API
• add a regression test for externally setting the controlled value to null while the popup exits
• add a public controlled-close docs demo for visual verification

Testing

• pnpm vitest run packages/react/src/navigation-menu/root/NavigationMenuRoot.test.tsx --project @base-ui/react
• pnpm --filter docs typescript
• Manually verified the docs demo at /react/components/navigation-menu: unchecking "Menu open" applies data-ending-style with frozen popup dimensions

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4855
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4855
  

commit: 2f7c24b

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+174B(+0.04%)	🔺+55B(+0.04%)

Details of bundle changes

Performance

Total duration: 1,317.26 ms 🔺+243.57 ms^(+22.7%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 1,994.30 ms 🔺+339.48 ms^(+20.5%)

Test	Duration	Renders
Checkbox mount (500 instances)	97.84 ms 🔺+38.06 ms(+63.7%)	1 (+0)
Menu mount (300 instances)	151.25 ms 🔺+34.58 ms(+29.6%)	2 (+0)
Select mount (200 instances)	169.10 ms 🔺+33.48 ms(+24.7%)	3 (+0)
Slider mount (300 instances)	177.23 ms 🔺+30.16 ms(+20.5%)	3 (+0)
Mixed surface mount (app-like density)	90.37 ms 🔺+23.65 ms(+35.4%)	5 (+0)

…and 3 more (+4 within noise) — details

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