When data-anchor-scene-live-owner=1, the #2403 legacy interim_assistant collapse toggle
('Show N earlier updates') is now cleared in renderLiveAnchorActivityScene cleanup AND the
interim_assistant SSE handler skips creating it. Guards both directions; regression test
locks the invariant. messages.js + ui.js. 289 interim/anchor/worklog tests pass.
Co-authored-by: nesquena-hermes <agent@nesquena-hermes>
Co-authored-by: franksong2702 <franksong2702@users.noreply.github.com>