DustCloudBackupSource

Optional cross-device source of a dust checkpoint (e.g. Google Drive). The concrete implementation lives in sdk:wallet-runtime (it needs Drive + the backup crypto); core:indexer and this module stay transport-agnostic.

DustSyncManager consults this once, on a cold start with no local checkpoint, before falling back to a genesis sync. Any failure must surface as null/throw and degrade cleanly to genesis — never block or crash a working wallet.

Inheritors