Several comments still described an Argon2-only worker: the class summary,
the thread name, the log message, and the dev-docs entry. The worker runs
whichever protection an account stores.
Trimmed the rest to the fact a reader cannot recover from the code, and
dropped the narration around it.
Adds a sixth worker rule to the threading model, which is the one this branch
actually learned: everything a worker calls must itself be safe off-thread,
and a process-wide singleton is not automatically safe. HashAlgorithm carries
the running digest across HashCore/HashFinal, and Utility's RNG is a shared
System.Random and game state besides. Both were reasons the worker had been
narrowed to Argon2, and both were better fixed at the source.
9434743a35