Placing WAL records into files in work directory (preallocated size; files with same name) was intitially done for perfomance reasons.
But for case there is no activity in the system there is no need to keep open segment in work directory.
It is possible move data of this incomplete segment into archive.
Proposed change: wait some configurable time, e.g N minutes and move WAL segment to archive.
This operation should be done with appropriate lock held to avoid writting record to WAL segment which is being archived.