The 'Install the update' button posts to
option=com_joomlaupdate&layout=update (Joomla's confirm/updating page),
carrying only layout=update -- no view, no task. The redirect matched
view=update / update.install, so it never fired on the Joomla Update page.
Match layout=update (plus view=update and legacy update.install), and
return the browser to the same layout flagged is_backed_up=1.
Claude-Session: https://claude.ai/code/session_01WbGBN9VyRK61zczYWcCQ2i