More resilient token exchanges when migrating tokens without a user session

Summary

• Apps can retry token exchange for up to 7 days using the original non‑expiring offline token to recover lost migration responses without a user session.
• The eligible retry returns the same access‑token/refresh‑token pair, extends the access token’s expiry when needed, and does not extend the refresh token’s expiry.
• Recovery ends after 7 days, a successful refresh, or a later token acquisition; the original non‑expiring token must be discarded.