When the Duo folded while the other tab held a detail, that tab's list
column was covered by the collapse but saw the folded search placement
only on returning, after the tab switch had cleared the detail. The
header kept its old search controller, which UIKit never re-placed, so
the folded pull request list came back without its search.

The header now gives search a new controller when the placement changes
and the column was covered on either side of that change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>