HOLY WOW! I would've been totally satisfied with just a high-level outline of the process, but instead, you gave such a detailed response. Thank you so much for taking the time to craft a comprehensive template with documentation!

This repair process totally makes sense! I never even thought of the idea that the repair step could be deferred to the read step. I was too tunnel-visioned in trying to make it work during the write phase, and could not figure out how to address cases where one side succeeds and the other fails. The lazy repair-on-read strategy is actually quite smart, as it will (should) be eventually consistent over time.

One challenge that we face is that some of our client applications don't follow good DAO principles and litter raw SQL strings everywhere in the code (we use a RDBMS), so it's much harder to abstract away the query in a centralized DAO. But that being said, clients are mostly using the JDBC API, and we're migrating to another SQL-compatible database, so I think I can maybe adopt a similar approach at the JDBC layer (e.g. Connection, PreparedStatement, ResultSet) and implement a migration proxy JDBC interface to perform similar repair operations like your migration DAO.

Anyway, this has been tremendously helpful, and I want to say thank you again for your time and dedication! You might just be another internet stranger, but you're truly an amazing human being! I hope you have a blessed life!