It would be nice for a thing calling itself "fail-safe" to have some amount of formal evidence of its fail-safe properties by way of both checked abstract model

It would be nice for a thing calling itself "fail-safe" to have some amount of formal evidence of its fail-safe properties by way of both checked abstract models & verified source/binary level implementation (I also think the same thing about everything posted here related to security too). I browsed through the repo and didn't see anything other than what amounted to narrowly targeted unit & integration tests. The test scripts are mostly in Python, so even just some Hypothesis tests (property-based testing framework for Python) would be nice to try to quasi-brute force some more empirical assurance that this filesystem behaves as claimed and expected. That said, this is likely to come in very handy, and seems definitely worth taking a look at.