If a remote commit is downloaded that simultaneously removes an agent from
desk.bill but also removes the associated source files, then the commit
will fail as gall will not have received the card to kill the agent yet.
Instead, we read our foreign copy of the bill in +take-download, and
kill any necessary agents there, preventing a reload of the deleted
agent from occurring.
When we receive the %mere gift from clay, the kernel has not yet been
reloaded. This means any attempts to bump desks will fail, as they will
be bumped against the old kernel. Rectifies this by continuing the %base
desk update flow in +on-load, instead of +take-merge-main. Also adds a
wef=(unit weft) to the state in order to discriminate whether or not the
kernel has just been reloaded
