[select] Skip disabled items in typeahead and fix multiple-mode serialization

[atomiks]

Summary

Fixes a few Select correctness issues plus adjacent cleanup, with regression tests.

Bugs

• Typeahead now skips disabled items. Disabled items register their value/label unconditionally and useTypeahead only skipped invisible elements, so typeahead could stop on a disabled item (and, on a closed trigger, commit it). It now skips disabled items while matching, so a single keypress advances to the next selectable item — matching native <select> and arrow-key navigation — in both open and closed states. This is done via a new opt-in isIndexDisabled predicate on useTypeahead, decoupled from the elementsRef/visibility filter so Select's mounted-but-hidden closed items still match. Menu and Combobox don't pass it, so their behavior is unchanged.
• Multiple mode no longer passes the whole value array to itemToStringValue. The shared hidden input is nameless in multiple mode (per-value <input>s carry the data), so serializedValue is now ''; previously a user itemToStringValue written for a single item would throw or yield ''.
• positionerElement.style.maxHeight = 'auto' (invalid, silently ignored) → 'none', so the explicit height governs in align mode and isn't clamped by user CSS.
• Trigger callback refs no longer fire twice (they were attached via both a merged-ref prop and the useRenderElement ref array).
• A custom isItemEqualToValue is no longer handed the raw empty array as the "selected value" in multiple mode (undefined when nothing is selected).

Cleanup

• Remove the write-only keyboardActiveRef and the unconsumed events context field.
• Use ownerWindow(el).getComputedStyle(el) in SelectPopup (repo convention for realm-sensitive lookups).
• Drop a stray useStore argument in SelectArrow and unused scroll-arrow refs.
• Comment fixes (backdrop description + generated docs, parseFloat fallback, outside-press); remove a shipped XXX note.

Tests

• Typeahead skips a disabled item and commits the next match.
• Commits nothing when the only typeahead match is disabled.
• Multiple-mode itemToStringValue isn't invoked with the array.

Typecheck, eslint, prettier, and the Select / Menu / Combobox / useTypeahead suites pass. Based on current master.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@5025
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@5025
  

commit: 78d89a5

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	▼-236B(-0.05%)	▼-53B(-0.04%)

Details of bundle changes

Performance

Total duration: 1,352.76 ms -101.49 ms^(-7.0%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 2,057.49 ms -126.90 ms^(-5.8%)

Test	Duration	Renders
Checkbox mount (500 instances)	78.13 ms ▼-35.97 ms(-31.5%)	1 (+0)

11 tests within noise — details

---

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

[netlify]

✅ Deploy Preview for base-ui ready!

Name	Link
🔨 Latest commit	78d89a5
🔍 Latest deploy log	https://app.netlify.com/projects/base-ui/deploys/6a2baa9e57815e0008719e1b
😎 Deploy Preview	https://deploy-preview-5025--base-ui.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

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

[Copilot]

Pull request overview

This PR fixes several Select correctness issues, centered on typeahead behavior and multiple-mode form serialization, and adds regression tests to prevent future regressions.

Changes:

• Extend useTypeahead with an optional isIndexDisabled predicate and use it in Select to skip disabled items during matching (including closed-trigger typeahead).
• Fix Select multiple-mode serialization so the shared hidden input doesn’t attempt to stringify the entire selected-value array.
• Misc. Select cleanup (remove unused context fields/refs, realm-safe getComputedStyle, ref wiring) plus regression tests and doc/comment corrections.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/react/src/select/trigger/SelectTrigger.tsx	Ref wiring cleanup to prevent duplicate ref-callback firing; clarifies outside-press mouseup handling.
packages/react/src/select/root/SelectRootContext.ts	Removes unused context fields (events, keyboardActiveRef) and unused import.
packages/react/src/select/root/SelectRoot.tsx	Multiple-mode serialization fix; integrates disabled-skipping into typeahead via new hook predicate; removes unconsumed events plumbing.
packages/react/src/select/root/SelectRoot.test.tsx	Adds regression tests for multiple-mode serialization and disabled-skipping typeahead on closed trigger.
packages/react/src/select/popup/SelectPopup.tsx	Uses realm-safe ownerWindow(...).getComputedStyle(...); fixes maxHeight assignment; removes unused refs.
packages/react/src/select/item/SelectItem.tsx	Ensures custom equality function isn’t called with the raw empty array in multiple mode.
packages/react/src/select/backdrop/SelectBackdrop.tsx	Corrects component doc comment (“select popup”).
packages/react/src/select/arrow/SelectArrow.tsx	Removes a stray unused argument passed to useStore.
packages/react/src/floating-ui-react/hooks/useTypeahead.ts	Adds isIndexDisabled option and skips disabled items while matching.
docs/src/app/(docs)/react/components/select/types.md	Updates generated docs text to match Select terminology (“select popup”).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.