Returns a refreshed token state if a refresh happened (the executor uses it immediately for
the in-flight request), or undefined if no refresh was needed or possible. Must not throw —
refresh failures are caught internally and reported via undefined so the caller falls back
to the existing token.
Returns a refreshed token state if a refresh happened (the executor uses it immediately for the in-flight request), or undefined if no refresh was needed or possible. Must not throw — refresh failures are caught internally and reported via undefined so the caller falls back to the existing token.