The streaming caret (::after on the running message's last child) was an
in-flow inline-block adding ~0.78em of inline width, which could wrap the
last line mid-stream; when the caret is removed on completion the line
un-wraps and reflows — the visible post-response layout shift. Net-zero its
inline advance with a compensating negative margin so it paints at the text
end without consuming layout width.
Brooklyn Nicholson
815f171f37