The posix hand-off hands marker line 1 to a custodian subshell
(marker_refresher_start) and then exported HERMES_UPDATE_HANDOFF_PID="$$" —
the hand-off script's own pid.
`hermes update` adopts a live claim only when the owner is its own pid, the
HERMES_UPDATE_HANDOFF_PID value, or an ancestor
(update_lock.UpdateLock._is_partner). The custodian is a *sibling* of the
hand-off script, so it is none of the three and the ancestry walk can never
reach it: every desktop-initiated update refused the claim its own script had
just made and exited 2 ("Another Hermes update is already running ...
process <custodian>"), leaving the Desktop to relaunch and retry forever.
Export $MY_PID instead: the custodian once the handover succeeded, and the
script's own pid when it did not.
Fixes#134268
013e94b38a