Slate React focus tests need Vitest with jsdom 20, not Happy DOM or jsdom 26

Problem

packages/slate-react/test/react-editor.vitest.tsx had one focus/selection row that Bun could not carry honestly.

The failing case was:

• ReactEditor > .focus > should be able to call .focus without getting toDOMNode errors

Jest passed it. Bun did not.

Symptoms

• Bun + Happy DOM returned the old "test" node instead of "bar".
• Bun + an ad hoc JSDOM preload returned "foobar" instead of "bar".
• Vitest + Happy DOM still returned "test".

Those were three different setups, but none matched the old Jest result.

What Worked

Use a split runner for slate-react:

• keep the existing Bun lane for packages/slate-react/test/bun/**
• move the remaining test/*.vitest.{ts,tsx} lane to Vitest
• run the Vitest lane on jsdom 20.0.3

With that environment, the full slate-react non-Bun spec lane went green, including the ReactEditor.focus(...) row.

Why

This was not just a “Bun vs Vitest” choice.

The real seam was DOM environment fidelity on focus/selection behavior:

• Happy DOM was not faithful enough for this row.
• newer jsdom also did not match the old expectation here.
• the old Jest lane was effectively proving against the older jsdom contract.

Prevention

• For slate-react DOM/focus tests, do not assume Bun + Happy DOM is lossless.
• If a row is selection/focus sensitive, compare the exact DOM environment, not just the test runner.
• When replacing Jest, check the jsdom version it was implicitly using before blaming the product code.