Depending on metadata cache behavior configuration, if the system is powered off immediately after the first command, then that could indeed happen I think.
As to whether it’s technically possible for it to happen on a system that stays on, I’m not sure, but it’s certainly vanishingly rare and likely requires very specific circumstances—not just a random race condition.
Uhh, if the system powers off immediately after the first command (mv a b), the second command (mv c d) would never run. So where would d come from if the command that created it never executed?
Er, sorry: I meant: if the first command runs, the plug is pulled, system starts again, second command runs.
Sure, but splitting "atomic" operations across a reboot is an interesting design choice. Surely upon reboot you would re-try the first `mv a b` before doing other things.