## What changed
- Prefer an eligible account grant over saved enterprise credentials, with a fallback to saved enterprise sign-in during initial connection if the account grant is rejected.
- Remember rejected account grants per enterprise MCP registration across threads and report authentication failures as requiring reauthentication. Keep administrator configuration errors distinct from sign-in failures.
- Compare account grants independently of access and ID token rotation, recheck the latest identity eligibility after exchange, and retry once when the refresh grant changes.
- Make MCP authentication status reflect usable account grants, saved enterprise credentials, and completed connection failures.
## Testing
Extend regression coverage for enterprise sign-in failures and recovery, MCP authentication status, account grant identity across token refreshes, and retries after transient credential failures.
GitOrigin-RevId: eeac65f668d5d2d55e9d8bf4547fbcbdd6a6c42d
jif
c419fd01a7