[select] Fix mouse selection in StrictMode dev

[uixmat]

Summary

• Re-sync CompositeList elementsRef from sortedMap on each layout effect run so list navigation can resolve live DOM nodes after StrictMode cleanup wipes refs without re-running item ref callbacks
• Fixes mouse selection in Select (and other composite list consumers) in React StrictMode dev environments such as Next.js dev

Fixes #4698

Test plan

• pnpm test:jsdom CompositeList --no-watch
• pnpm test:jsdom SelectRoot --no-watch
• Manual verification in docs dev: open select, click item, value commits

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+58B(+0.01%)	🔺+17B(+0.01%)

Details of bundle changes

Performance

Total duration: 1,510.19 ms 🔺+261.18 ms^(+20.9%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 2,297.37 ms 🔺+401.98 ms^(+21.2%)

Test	Duration	Renders
Tabs mount (200 instances)	291.81 ms 🔺+66.02 ms(+29.2%)	4 (+0)
Menu mount (300 instances)	172.98 ms 🔺+35.82 ms(+26.1%)	2 (+0)
Select mount (200 instances)	179.97 ms 🔺+35.69 ms(+24.7%)	3 (+0)
Scroll Area mount (300 instances)	116.96 ms 🔺+29.05 ms(+33.1%)	3 (+0)
Mixed surface mount (app-like density)	96.34 ms 🔺+23.41 ms(+32.1%)	5 (+0)

…and 2 more (+5 within noise) — details

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[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4897
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4897
  

commit: 4ba115b

[atomiks]

@uixmat thanks for the fix — mouse selection without highlight was already fixed in #4699, so the tests should prove that [data-highlighted] is correctly set in Strict Mode. I have a feeling it may not be reproducible in our test env though.

Note this also adds an extra O(n) scan just to fix a rare dev mode problem, ideally it would be cheaper.

[uixmat]

@uixmat thanks for the fix — mouse selection without highlight was already fixed in #4699, so the tests should prove that [data-highlighted] is correctly set in Strict Mode. I have a feeling it may not be reproducible in our test env though.

Note this also adds an extra O(n) scan just to fix a rare dev mode problem, ideally it would be cheaper.

No problem, go-ahead and close the PR if you like, i'll hunt down some other issues!