The unread-boundary effect bailed out entirely once it gave up paging
toward the target, so a channel whose oldest unread sat further back
than the four-fetch cap never offered the jump control again for that
visit, even after the user scrolled the target into view themselves.
Scope the give-up flag to fetching, which is what it is for, and let
candidate resolution keep running. Direction of the bug was fail-closed
(a missing control, never a wrong jump), so this only restores a
control that PR #4239's predecessor head offered.
Co-authored-by: Tom Brow <tomb@block.xyz>
Signed-off-by: Tom Brow <tomb@block.xyz>
bde10f65cf