Instead of spawning these when players first log in and have the
entities update their state on_step, just run a single globalstep
that walks across all players and inventories, and then across all
entities, in a couple of passes, and reconciles everything.
This should also deal with entities that are lost for random or
arbitrary reasons, which seems to be the remaining known cause of
wield items spontaneously disappearing.
The code is also simpler (a single loop with a few linear passes)
and probably more efficient.
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