Arcana::Events

Append-only event log for the Arcana bus.

Every material action (registrations, sends, publishes, freezes, auth events, lifecycle) is recorded as an Event and written to a Backend. The default FileBackend stores JSONL files with daily rotation, gzip compression of older days, and time-based purge/archive retention.

Privacy: the event log stores metadata only — addresses, subjects, correlation IDs, timestamps, sizes. Envelope payloads are not persisted. If replay-based durability is ever needed, that would be a separate "journal" stream with different retention and access rules.

Enterprise / future work: tamper-evident logs (hash-chained events, Merkle-tree periodic checkpoints) for audit compliance. Today's FileBackend is trust-the-filesystem. When a customer needs cryptographic audit guarantees, a TamperEvidentFileBackend (or a separate AuditBackend) can layer on top — each event carries the hash of the previous event, and a signed daily checkpoint ties the chain to wall time. Deliberately scoped out for now.