test(coverage): close clean JVM-testable coverage gaps
Close the cleanly JVM-testable coverage gaps from the Phase-2 JaCoCo
audit (#288), bringing each targeted class to 100% line coverage:
- AccountSettingsRepository: observe Flow + the sibling setters
(signature/notifications enabled, retention count/months incl. clamp).
- SignatureRepository: observeForAccount/get/getDefault/update + toDomain.
- CredentialStore (new): save/load/delete with a mocked KeystoreCrypto.
- EncryptedCacheGuard (new): the isCacheLocked() truth table.
- AttachmentUriGrants: releaseUnreferenced/referencedUris wiring.
- SyncScheduler: schedulePeriodicReportPurge.
- AppLockViewModel: nonce, onBackground cover branch, unwrap cancellation
rethrow, awaitSyncEnqueue execution/interrupt branches.
- SmtpSender: send error paths (SSL/STARTTLS) + cc + inline+regular body.
- StartupReportViewModel: the @Inject real-clock constructor.
All test-only. Unit tests + jacocoTestReport + ktlintCheck + detekt green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
JMR-devandClaude Opus 4.8
a6c24f3cea