Interestingly, this prefix rule which is based on the filesystem-based ref storage is enforced even if refs are stored via alternative means like .git/packed-re

Interestingly, this prefix rule which is based on the filesystem-based ref storage is enforced even if refs are stored via alternative means like .git/packed-refs, since the refs could later be stored in the filesystem. You can verify this by calling `git pack-refs --all` and verifying that your .git/refs/heads directory is empty but you still cannot create conflicting branches.