In classic I needed a 3-state.

Hmm, sorry, this platform is confusing. I only now see the full diff... (the previous comment was regarding the assert).

Good catch!

This approach may end up breaking initial-block validation.

FYI; the CheckForkWarningConditions() and friends use hard-coded block-counts and show a warning of a nature that I'm not sure is of any value. As such this code has been removed in Classic.

you can find 5 commits made on the 1st of Aug that comprise this feature;

If this changes the on-disk file-format then you will break compatibility of the on-disk structures with Classic and maybe others. The result being that users can no longer switch clients without doing a full re-sync.

Your src/test/net_tests.cpp changes should not have been in this commit. Actual content is looks fine. I didn't actually test this, though.

You might want to base this on;
https://github.com/bitcoinclassic/bitcoinclassic/commit/d893b7e62e2b54710b042315a0d0a0958c513834
and
https://github.com/bitcoinclassic/bitcoinclassic/commit/aaa6ba45bfeb10d82e0564267c8ac1d18d2eabcf

Thanks for subscribing me to this task.