Good question! They get marked as such and then typechecked as part of the early work before metadata is written/sent out. If they error out, crate fails, nothing happens, same as today. In practice, on the crates I was testing, there was more "regular" functions than these, so we could still get some good perf gains. https://github.com/PowderworksCode/headstart/blob/1c9d5cd691... https://github.com/PowderworksCode/headstart/blob/1c9d5cd691...

Additional information about potential downsides and prior art (including links to the previous time that this was attempted, in a slightly different form): https://github.com/PowderworksCode/headstart/blob/main/docs/...