[field] Publish neutral validity while async validation is in flight

[atomiks]

While an async validate function is in flight, the field published data-valid (a fresh all-clear from native constraints) even though the result is unknown, and only validationMode="onSubmit" retired the previous result. It also dropped known native failures in that window, so a required or type="email" field could submit past its native constraint when paired with an async validator.

The pending window now maps to the existing neutral state (valid: null, no data-valid/data-invalid/aria-invalid), consistently across modes. The only results kept mid-flight are the ones the form must read synchronously to block submission:

• native constraint failures, published in every mode
• a previously resolved async error in onChange/onBlur (async results can't block in onSubmit mode, per the validate docs)

A previously valid result retires in every mode, so no stale success shows for a value that was never validated.

publish/makeValidityData accept valid: null internally; public types already allowed it.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@5600
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@5600
  

commit: ef9fe18

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+60B(+0.01%)	🔺+29B(+0.02%)

Details of bundle changes

Performance

Total duration: 1,224.35 ms 🔺+258.15 ms^(+26.7%) | Renders: 76 ⁽⁺⁰⁾ | Paint: 1,960.74 ms 🔺+403.68 ms^(+25.9%)

Test	Duration	Renders
Tabs mount (200 instances)	277.25 ms 🔺+84.38 ms(+43.7%)	3 (+0)
Select mount (200 instances)	137.87 ms 🔺+25.40 ms(+22.6%)	3 (+0)
Slider mount (300 instances)	130.37 ms 🔺+22.91 ms(+21.3%)	2 (+0)
Menu open (500 items)	80.36 ms 🔺+18.86 ms(+30.7%)	11 (+0)
Menu mount (300 instances)	95.40 ms 🔺+16.58 ms(+21.0%)	1 (+0)

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

Metric alarms

Test	Metric	Change
Tabs mount (200 instances)	bench:paint	🔺 +107.95 ms
Select mount (200 instances)	bench:paint	🔺 +37.77 ms
Slider mount (300 instances)	bench:paint	🔺 +47.74 ms
Menu open (500 items)	bench:paint	🔺 +23.95 ms
Menu open (500 items)	bench:paint#menu-open	🔺 +23.95 ms

…and 10 more metric alarms — details

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

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