[combo-box] Fix applying data-readOnly for ComboboxTrigger

[sai6855]

readOnly was missing from the trigger's state, so the documented data-readonly style hook never rendered, even though the sibling Combobox.Input already emits it. Added readOnly to the state plus a test.

[sai6855]

data-readOnly wasn't added when root was set to readOnly. adding readOnly state here fixed the issue

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@5418
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@5418
  

commit: e246e74

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+11B(0.00%)	🔺+3B(0.00%)

Details of bundle changes

Performance

Total duration: 1,249.57 ms -13.19 ms^(-1.0%) | Renders: 78 ⁽⁺⁰⁾ | Paint: 1,980.78 ms +1.03 ms^(+0.1%)

Test	Duration	Renders
Mixed surface mount (app-like density)	88.74 ms 🔺+24.16 ms(+37.4%)	5 (+0)

14 tests within noise — details

Metric alarms

Test	Metric	Change
Mixed surface mount (app-like density)	bench:paint	🔺 +35.39 ms

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[Copilot]

Pull request overview

This PR fixes the Combobox.Trigger state so the readOnly flag is reflected in its state-driven data attributes (enabling the data-readonly styling hook), aligning it with how other components expose readOnly for styling.

Changes:

• Adds readOnly to ComboboxTrigger’s computed state so useRenderElement can apply data-readonly.
• Extends ComboboxTriggerState with a readOnly field.
• Adds a regression test asserting data-readonly is present only when readOnly is true.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/react/src/combobox/trigger/ComboboxTrigger.tsx	Includes readOnly in the trigger state so the data-readonly style hook is applied correctly.
packages/react/src/combobox/trigger/ComboboxTrigger.test.tsx	Adds coverage to ensure data-readonly toggles with the readOnly prop.

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