Upstream replaced MainFrame's fixed-index TabPosition enum with string-based
page ids ("feat: refactor notebook/tabs to be string based instead of fixed
index based"). The IMEX toolhead-visibility menu item was the only consumer of
that enum left on this branch, so its enable check now compares
m_tabpanel->GetSelectedPageName() against TAB_ID_PREVIEW -- the same form the
neighbouring upstream menu items use.
That mismatch is what broke CI: the branch built on its own, but the merge
commit CI builds no longer had TabPosition declared. No other conflicts.
666/666 tests pass in Release.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
