Task 9's first pass replaced inbound expiry's signed /peer/denied
POST with a plain delete, citing symmetric independent expiry as
the design. The spec at §4.10 explicitly said 'inbound row cleanup
unchanged' — that was scope creep, not a fix. Inbound expiry now
preserves the pre-branch behavior verbatim: signed POST to remote,
delete only on success, retry on failure. Outbound expiry's fanout
logic (the actual Task 9 scope) is unchanged.