It probably does not make sense to enable auto mode for move. I cannot
think of a situation where it would make sense to try to use it.
A hypothetical auto mode for move would only differ from a normal
move in one case -- when both repositories have a file, move deletes it
from one, and this reduces the number of copies. So an auto mode would
either only let move work in that situation, or avoid removing the file
in that situation, depending on the number of copies. This would be
complex to implement, and is perhaps not a very obvious behavior.
The error is a good thing to have, so users don't expect it to do something
it does not.
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