ISTM, your tests should serve as live documentation by providing runnable examples of how the code should work. A few higher-level architectural diagrams will supplement those. When the structure of the code and the underlying architecture reflects the domain exactly, as in a DDD system, if you understand the domain, you understand the code and architecture as well. I don’t see a need for additional documentation.

Source: x.com/allenholub/status/1832911991708794955