test(web): ChatMarkdown thread find waits for highlights to settle

[juliusmarminge]

ChatMarkdown.browser.test.tsx "highlights the indexed occurrences of SearchSourceAlpha in ```mermaid" flakes. It failed on #21118, which only touches the right panel test, and on an unrelated branch (run 39104001715). Both times it found [''] instead of ['SearchSourceAlpha'].

The test read the CSS highlights after a single animation frame. The Mermaid block renders lazily and can swap its source text after that frame, so the highlight range is briefly empty. The assertion now runs inside vi.waitFor. This test uses real timers, so waitFor actually polls. The neighbouring Mermaid test already waits the same way.

The thread-find tests pass 8 times in a row locally. Like the right panel flake, it never failed locally, so this rests on the reasoning above.

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[macroscopeapp]

Approvability

Verdict: Approved at f55388e

Macroscope's review found this PR approvable — This is a small, test-only change confined to an ignored path, adjusting assertion timing for asynchronously rendered highlights. It has no production runtime, product-default, schema, deployment, or static-analysis suppression impact.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

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• apps/web/src/components/ChatMarkdown.browser.test.tsx

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📝 Walkthrough

The thread-find highlighting browser test now waits for the expected highlight ranges to settle before checking their count and text. The expected results are unchanged.

Changes: Thread-find highlight test

Layer / File(s)	Summary
Wait for highlight ranges apps/web/src/components/ChatMarkdown.browser.test.tsx	The test uses vi.waitFor to retry the highlight-range assertion until every range matches the query and expected count.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to f5538

This test-only change waits for the expected highlights to settle without changing production behavior. No merge-blocking risk remains.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly identifies the web test change and the reason for waiting for highlights to settle. It is concise and follows the repository's conventional commit style.
Description check		The description explains the flaky behavior, expected behavior, root cause, code change, affected test, verification results, and tooling used. It does not use the template headings or explicitly stat…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the flaky behavior, expected behavior, root cause, code change, affected test, verification results, and tooling used. It does not use the template headings or explicitly state the scope or approval exemption, but the focused test-only change and linked CI failures provide sufficient context.

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