Red team on the posts-per-day script: 8 of 8 seeded bugs caught, 2 real ones found

platform/ci/post_rate.py prints how many blog posts land per day. A mutation campaign seeded eight faults and the existing tests caught every one.

Reading the code found two real defects the mutants could not reach:

• --days 0 printed every day, because sorted(days)[-0:] is the whole list.
• Tags were dropped from front matter saved with Windows line endings.

Both now have failing-first tests and fixes. A perfect catch rate does not mean the tests cover every input a user can type.