Thanks for letting us know about this. This was caused by a transient error in the infrastructure we use for running server code on the Free plan, and should now be resolved!
Me too, same, in Production Env. “RuntimeUnavailableError: Internal server error: Server runtime failed to start. on line 70”. In Develop Env. it works fine.
Update: This issue affecting Free Plan users will be resolved shortly. This time I managed to catch it “in the act”, and we should have a much better chance of tracking down this particular misbehaviour!