This is an interesting idea. I've been idly thinking about how to make a framework for detecting DB anomalies in Django applications (say, missing transactions,

This is an interesting idea. I've been idly thinking about how to make a framework for detecting DB anomalies in Django applications (say, missing transactions, race conditions, deadlocks etc.) which can be hard to detect. You can strap your application to Jepsen but this is a more white-box approach and probably harder to grok for the average Python developer. I like the OP's idea of using a virtual thread implementation to parallelize the application-layer, while having the test code implement a custom executor to control the interleaving of the units-of-work being scheduled. I can see a few ways this approach could be used more widely; for example in Django you could write a DB driver wrapper and have this as the "test executor". Or for remote API requests, run the test code in green threads and then have a test executor that intercepts and then then chooses how to interleave the requests/responses.