Resolve the PR #182 code-review (Request changes) on top of the already-merged
develop (the merge commit preserves both the markdown useMemo and the
collapseBlankLines fix in reasoning-block.tsx).
- Extract messageSignature from message-item.tsx into utils/message-signature.ts
(matches the feature's "pure UIMessage helper + colocated test" convention) and
export arePropsEqual so the memo seam is unit-testable. No logic change.
- Add utils/message-signature.test.ts covering every change signal (text grows,
part appended, state flip, output appears, errorText appears, usage.reasoningTokens
arriving on finish-step, metadata error/finishReason) plus the negative
content-identical-clone case.
- Add components/message-item.test.ts for arePropsEqual (each prop diff -> false,
identity fast-path -> true, same-content-different-object -> true, changed -> false).
- Add components/message-item-memo.test.tsx: render-level proof that finalized text
parts are not re-parsed when only a tail part grows (MarkdownPart memo).
- CHANGELOG: add the user-facing 100% CPU freeze fix under [Unreleased] / Fixed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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