Diagnosing "early termination of worker" errors

You might be trying to start your Rails server and getting something like the following, with no accompanying stack trace to tell you exactly what it is that’s gone wrong.

[10] Early termination of worker
[8] Early termination of worker

This is a note-to-self after encountering this when trying to upgrade a Rails app from Ruby 2.7 to 3.2. What helped me was a comment from this Stack Overflow post.

If rails s or bundle exec puma is telling you the workers are being terminated but not telling you why, try:

rackup config.ru
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