Step 4: the count goes to 0 inside the transaction and comes back after the rollback.
Step 5 returns only drafts that belonged to devon.
Your feed query excludes post 8 after step 6 and includes it again after step 7.
Step 8: you deleted one row and rows vanished from four other tables. You can name the line in your migrations that caused each.
You can answer: the index you built for the feed in Level 7 was WHERE published. Now the feed also filters on deleted_at IS NULL. What would you change?