The standalone "Thinking…" indicator's agent-name label switched owners a couple seconds into a turn: at first TypingIndicator rendered name+dots (4px gap), then once useChat materialized the empty/reasoning-only assistant message the name moved to the empty MessageItem row (16px messageRow margin), pushing the dots ~20px away — a visible layout jump.
Introduce a shared pure helper assistantMessageHasVisibleContent() as the single source of truth mirroring MessageItem's render decisions. MessageItem now returns null for an assistant message with no visible content, and typingIndicatorShowsName keeps the name on the indicator until the assistant row has visible content. Exactly one element owns the name throughout the pre-content gap, so the layout no longer reflows.
- new utils/message-content.ts + unit tests (12 cases)
- message-list.tsx: typingIndicatorShowsName uses the helper
- message-item.tsx: early return null when no visible content
- typing-indicator-shows-name.test.ts: updated expectations
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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