The "Copy chat" export read only persisted DB rows (messageRows), so an
assistant reply that was still streaming — and the user message that
triggered it — were absent from the export until the turn finished and
the messages query was refetched.
ChatThread now mirrors its live useChat snapshot ({ messages,
isStreaming }) into a parent-owned ref; the effect clears the ref on
unmount so a thread switch can't leak its tail into the next chat.
AiChatWindow.handleCopy computes the not-yet-persisted live tail
(messages whose id is absent from messageRows, only while streaming) and
passes it to buildChatMarkdown as `pending`. buildChatMarkdown appends
pending messages after the persisted rows (continuing the heading
numbering), flags the streaming assistant message with an
"still being generated" note, and reuses an extracted renderMessageParts
helper so persisted and pending rendering stay identical.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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