The floating AI chat rendered NOTHING for the assistant turn (user bubble +
"thinking" dots showed, but the streamed text and tool-call cards never
appeared) even though the agent ran server-side. The parts DID arrive in
`useChat.messages` — this was purely a render freeze.
Root cause: the MessageItem `React.memo` comparator (#182) decided whether to
re-render by recomputing `messageSignature(prev.message)` vs
`messageSignature(next.message)` inside `arePropsEqual` (plus a
`prev.message === next.message` fast path). But the AI SDK (ai@6 /
@ai-sdk/react@3) streams a turn by MUTATING the same `parts` in place and
handing back a message wrapper that SHARES those mutated parts. So inside the
comparator both `prev.message` and `next.message` already reflect the latest
content — the two signatures are ALWAYS equal — and the memo skipped every
post-mount render. The assistant row therefore froze at its initial empty
(null) render; reasoning-first providers (e.g. z.ai/GLM) start with a
non-visible reasoning part, so the whole answer + tool cards never showed.
Fix: snapshot the signature in the PARENT (MessageList) at render time and pass
it to MessageItem as an immutable `signature` string prop; `arePropsEqual` now
compares that prop. A captured string is immutable, so `prev.signature` holds
the previous render's content and `next.signature` the new content — they differ
as the turn streams in and the row re-renders. Drop the now-incorrect
`prev.message === next.message` fast path (same-ref-but-mutated must still
re-render). MarkdownPart's per-part memo is unaffected (it already keys on the
primitive `text`).
Verified end-to-end against a real OpenAI-compatible provider: the assistant
turn (reasoning + streamed text + tool-call card) now renders live and on
finish. Regression tests added (render + comparator) that fail before / pass
after.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Address non-blocking review items on the AI-chat stream-perf PR:
- Drop the unused `metadata` param from the `msg` test factory in
message-item.test.ts; no caller passed it.
- Add a per-part-kind coupling guard to message-signature.test.ts that, for
each part kind rendered today (text, reasoning, tool-*) plus the metadata
banners, asserts that mutating a field the MessageItem render body DRAWS
flips messageSignature — an executable lock for the load-bearing memo
invariant documented in message-signature.ts.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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>
claude code agent 227