Games can go out of sync when structures are miraged because NaN is serialized differently for different players. See #5030 for an example of how to produce the oos.
Mirage serializes buildTime from both Foundation and Repairable, and if there's no builders or repairers then timeRemaining = 0/0 = NaN. Unfortunately NaN isn't reliably serialized (see #1879 and further explanation in #1828), so in the meantime let's avoid using it.