Refreshes the OAuth tokens using the refresh_token grant. Concurrent
callers share a single in-flight request. An unrecoverable failure (a 4xx
rejecting the refresh token) clears the tokens and transitions to
LOGGED_OUT; transient failures (network, 5xx, rate limits) leave the
session intact and rethrow so the caller can retry.
Refreshes the OAuth tokens using the
refresh_tokengrant. Concurrent callers share a single in-flight request. An unrecoverable failure (a 4xx rejecting the refresh token) clears the tokens and transitions toLOGGED_OUT; transient failures (network, 5xx, rate limits) leave the session intact and rethrow so the caller can retry.