Implements AUDIT_REPORT.md H-3 (doc + retention), M-3, L-2/L-4 guidance:
- SECURITY.md: the deliberate data-at-rest posture (plaintext bodies + why, volume
encryption + backup guidance, DB TLS note, AllowedHosts note, production checklist,
delete-my-data procedure).
- Opt-in local data retention: DataRetention:{PurgeTrashedAfterDays,PurgeAllAfterDays}
(0 = disabled, no behaviour change) + daily RetentionWorker purging only the LOCAL
copy (Gmail untouched). 3 tests lock disabled-is-noop and purge-scoping.
- M-3: optional X.509 protection for the Data Protection key ring
(DataProtection:CertificatePath/Password) so keys are no longer necessarily
plaintext next to the ciphertext they protect.
Full suite: 51/51 green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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