[composite] Collapse grid navigation identity transform

[atomiks]

Summary

The grid navigator injected into useListNavigation only ever operates on a uniform 1×1 grid (sizes are always 1×1, packing is never dense), so the cell-map machinery is an identity transform: createGridCellMap returns [0..n-1], all corners coincide, the recomputed min/max equal the values passed in, and the disabled-index expansion is equivalent to passing disabledIndices straight through.

Collapsing it to a single getGridNavigatedIndex call:

• keeps createGridCellMap / getGridCellIndexOfCorner / getGridCellIndices out of grid-combobox bundles (they remain used by the real multi-cell composite grid navigator in internals/composite/root);
• drops the per-keystroke O(n) getComputedStyle scan the old min/max recomputation ran on every key;
• preserves the old cellMap[...] out-of-bounds behavior via isIndexOutOfListBounds, so a -1 sentinel still surfaces as "no navigation" rather than highlighting index -1.

Also renames a stale grid test describe block (sizes support is gone; the fixture is a uniform multi-column grid).

The useListNavigation and combobox suites pass; typecheck/eslint clean. 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@5027
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@5027
  

commit: 77ade07

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	▼-885B(-0.19%)	▼-336B(-0.23%)

Details of bundle changes

Performance

Total duration: 1,245.03 ms -209.22 ms^(-14.4%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 1,891.14 ms -293.25 ms^(-13.4%)

Test	Duration	Renders
Checkbox mount (500 instances)	70.52 ms ▼-43.57 ms(-38.2%)	1 (+0)
Select mount (200 instances)	136.86 ms ▼-37.66 ms(-21.6%)	3 (+0)
Popover mount (300 instances)	61.00 ms ▼-16.52 ms(-21.3%)	1 (+0)

9 tests within noise — details

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[Copilot]

Pull request overview

This PR simplifies the grid navigator injected into useListNavigation by removing the unused “cell map” indirection (which is an identity transform for the 1×1 uniform grid used there) and calling getGridNavigatedIndex directly, while preserving the prior out-of-bounds/-1 sentinel behavior.

Changes:

• Refactor hooks/gridNavigation.ts to call getGridNavigatedIndex directly and translate out-of-bounds results to undefined.
• Remove now-unused cell-map helpers/constants imports to improve tree-shaking for grid-combobox consumers.
• Rename a useListNavigation grid test describe label to reflect the actual fixture scenario.

Reviewed changes

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

File	Description
packages/react/src/floating-ui-react/hooks/gridNavigation.ts	Collapses identity cell-map logic into a direct getGridNavigatedIndex call and preserves sentinel behavior via isIndexOutOfListBounds.
packages/react/src/floating-ui-react/hooks/useListNavigation.test.tsx	Updates a grid navigation describe block name for clarity/accuracy.

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