MUNI's shortcomings are visible during rush hour due to system collapse, and off-hours / on secondary routes due to missing runs or too-infrequent scheduling.
Moving around the most urban cores outside of rush hour, you typically won't see the worst of the warts.
Yeah, you have to remember that in pulse dial days a central office station had a reach of roughly 3 miles. The longer you go, the more you're paying for cable, repeaters, or just losing quality. 90 volt AC for ringing has a limited range!
Buuuuut.... not if you hijack the destination route. It helps if the DNS servers are hijacked, but if you also snag the destination route's IP then you can still get the certificate and serve traffic. Sneaky sneaky.
Removal performance of large directories is very bad. Reading large directories can result in lots of seeks. Directories are not suited to this at scale, and symlink directories definitely aren't portable.
A side note: at least in python, I benchmarked MsgPack as 3 times faster than JSON, and a whopping 850 times faster to read than YAML. It seems unlikely that people will ever be editing this file by hand, so for unstructured data, especially where playlists can get very large, I suggest MsgPack over YAML.
BUT... you have a defined schema, so it's probably to your advantage to use a storage format with a defined schema: ProtoBuf or Thrift. That would mean somebody trying to use your code would already have generated objects in their language.
As for the hashing algorithm, this is a good use for MD5 -- cheap and fast. You're unlikely to be concerned about somebody actively trying to generate the same checksum for two music files. For non-security (integrity verification) purposes, MD5 is still very appropriate.
It depends on which 2FA method you use, and there's an associated time window. The TOTP method (Google Authenticator App) of a rotating number must be used within a window of at most a few minutes -- new numbers are generated every 30 seconds, so they could use that if they logged in immediately.
If you use U2F, then the domain name difference will mean that the U2F key can never match unless the attacker has control over DNS and is issued a Google.com SSL certificate by an authority the target's computer trusts.
Moving around the most urban cores outside of rush hour, you typically won't see the worst of the warts.