Hello,

In this context, the old deployment exited with a non-zero exit code and is therefore counted as a crash.

Thanks—how can I see the old deployment exiting, and/or how can I stop it exiting with an error code? Other than these emails, there's no sign I can see of anything wrong.

(I'm using Railway's Railpack)

You can open the old deployment's logs. As for debugging, unfortunately, we cannot help debug user applications, but I can open this up to the community if you would like.

This is the end of the last deployment's logs. What indicates an error?(You see Rails logs and SolidQueue logs interleaved here, but they both seem to exit happily.)

The application exited with an error. Your application doesn't necessarily need to print errors to exit with an error code.

But as mentioned before, we cannot help debug user applications. I can open this up to the community if you would like; otherwise, we would have to disengage here.

Ok, thanks. Yes, open to the community please.

Is there any way I can see the exit code?

Exited with a non zero exit code ..so its a crash ..from logs..try adding RAILWAY_DEPLOYMENT_DRAINING_SECONDS as a service variable to give SolidQueue time to finish in flight jobs before forced termination..To stop getting emails / non 0 exit code add exec to your start command
rake db:prepare && bin/rails assets:precompile && exec bin/rails server -b 0.0.0.0 -p ${PORT:-3000}