> but more important to our assurance of the model that it is byte-for-byte reproducible by us, as to prevent these "sleeper agents" from appearing.

That's neither necessary nor sufficient.

We don't know how to detect sleeper agents in the first place, and the ability to induce behaviour from crafted training data is already being used by artists to "poison" their portfolios so they cannot be used by model makers, therefore it is not sufficient.

When (or if, I suspect it's NP-hard) we do figure out how to find sleeper agents, a hash of the weights against a known-good version is an alternative to re-running an entire training process.