Over 700 years. A tower originally built in 1310. The island it’s on is an exclave that is technically part of Hamburg.

Without some sort of reproducible builds (which are really finnickey to actually get) this doesn’t really help though. Adding some set of malicious patches before doing the binary release is trivial.

Blockchains have the property of being append-only, so a blockchain is precisely what makes it impossible to delete transactions. That being said, in a distributed system, once the message leaves trusted servers, it is obviously also impossible to delete it.