Written for a cold reader and for the blog: the two-part mechanism (upstream header-only
reads + our own flag left flipped), why whitelist-by-mtime made it look haunted, the
count assertion catching its own counting bug on the AppleDouble twins, the 'Required
0 MB' red herring, and the two harness failures (zsh word-splitting, an early readiness
gate) that cost more time than the bug itself.