* refactor(imap): consume the core identifier-authentication scale
Use the SDK type and canonical strength comparator instead of the private
SenderStrength vocabulary and index ordering. Bind config values to the SDK
union with a compile-time exhaustiveness check, preserving all config keys.
Classify unproven From ownership, including no-evidence and DMARC temperror
results, as unverified. Only an explicit unverified minimum gains admission;
the default verified floor and asserted minimum keep their behavior. Keep
existing token admission and thrown-authenticator retries unchanged.
Document the remaining mutable token/early-rejection paths and expose only
the canonical comparator through the SDK, with packaged-consumer coverage.
The IMAP introduction has no stable release contract.
* docs(security): record landed sender-auth mitigations in the threat atlas
Record the graded exact-pair identifier-authentication gate and inert mutable
allowFrom audit findings. Mark R-008 implemented in core while retaining
per-channel verified adoption and downstream mappers as remaining work.
Keep the existing atlas structure and Medium residual risk.
Peter Steinberger