`token_path`'s doc claimed the compiler was the check and that nothing had to
remember to perform one. True of `agent`, which is an `Ident`. Not true of
`account`, a bare `&str` concatenated into the filename — safe only because
`deliver` happened to validate it first, which is the caller-must-remember
pattern the comment denied.
Observably a no-op today: the one call site already rejects a bad account
before reaching here. What changes is that the signature now enforces what the
comment asserted, so a second caller cannot skip it.
The check is `path::checked_segment`, made public rather than reimplemented.
Two copies of a charset are two charsets: they agree until one is edited, and
the day they diverge a name is legal in the store and not on disk.
An account name cannot simply become an `Ident` the way an agent name is:
it is an attribute name in `hyperhive.matrixAccounts`, so uppercase and
underscore are already configurable, and narrowing that is a decision rather
than a refactor. The new test's controls pin both.
Found by argus reviewing the merged PR.
6de6bd5d87