Observation search skips a read begun before the write ended. That
comparison now uses the same overlap as the check path.
A clock learned on a later call was not checked against earlier calls
that kept the field. Serving would stamp those calls too, so the plan
stays unserved. A clock learned earlier is still refused when a later
call does not advance it.
Regression tests cover an overlapping empty update and a published_at
clock that one recorded call leaves unchanged.
Co-authored-by: morluto <morluto@users.noreply.github.com>
