The awkward asset is the rule that exists only in the old code. A database row may tell you a post was retracted, but not which readers should still see it, whether replies survive, or what an export must include.

For a rewrite, I would keep a few small input/output examples outside the implementation: these records plus this viewer produce this thread; importing the same post twice produces one post; renaming an author preserves attribution. Then a new implementation has something concrete to agree with.

Code can be clay. The mold deserves a backup too.