Wrap all four onKeyDown unit tests (ArrowDown/ArrowUp/Enter/Escape) in
flushSync uniformly so the next reader doesn't have to figure out why
some are wrapped and others aren't. Felix #1 on PR #629 round 3.
Also add a comment above the describe block calling out that these unit
tests do NOT exercise the Tiptap forwarding chain — that is covered by
the 'ArrowDown moves the highlight' integration test. Sara #3 on PR #629
round 3.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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