An account's manager runs only while it is logged in or lingers. A user-scoped unit
whose manager is not running is now "waiting" rather than failed, its record kept as
it was; its removal is never fatal (kept recorded, retried) and an account that is
gone is forgotten. Whether the manager runs is asked of user@<uid>.service in the
machine's manager: asking the account's own, through --machine, logs it in.
The user shape gains `linger`, set with loginctl, read back from logind's record,
and given back on removal like the shell. Unit files the mesh writes under
~/.config/systemd/user or /etc/systemd/user make that unit the mesh's, and made,
holds and found units are keyed by manager and name, so an account's unit and the
machine's of one name are two units. A service moved between managers gives the old
one back through the manager it was in. OpenRC refuses both.
Records written before Found existed left the adoption guard and the converge filter loaded on
undeclare, then deleted their unit files from under them; a unit whose own file the mesh created
is now the mesh's, whatever its record says. Found is kept apart the moment it is read, so a
first apply that enabled and then failed is not read back as the machine's; boot is found the
first time the mesh sets it; a service once stateless, or moved to another unit, is found afresh
(the old unit given back). The unit is read after the reload that loads a file written in the
same apply, and removal reports what it actually did.
jochen