If you build one thing from this chapter, we would build this. It is the hardest to produce without really having done the work.
The log of past failures
Also called Ratchet log, Failure log
A running list of mistakes: what went wrong, what now prevents it, and proof that the check fails on the old code. It shows you noticed a failure, generalised it, and closed it off.
An agent can write you a convincing list of failures in a minute, so the entries are worthless by themselves. The proof is what counts. Run the check against the old code and it has to fail, and that is a thing someone can repeat in front of you.
“Add an entry to docs/failures.md: the date, what went wrong, the commit with the old code, and the check that now catches it. Then check out that old commit, run the check, and paste the failing output into the entry. If it passes on the old code, the check is wrong, so tell me.”