Reliability semantics
Fibril currently targets best-effort at-least-once delivery.
Durability
Section titled “Durability”Queue state is backed by append-only logs through Keratin:
- message log
- event and state log
- snapshot and replay
Commands are designed to be idempotent and replay-safe.
Acknowledgements
Section titled “Acknowledgements”Acknowledgements are explicit, idempotent, and final. A bounded ACK window tracks out-of-order acknowledgements near the monotonic settled_until frontier without requiring unbounded memory.
Retries
Section titled “Retries”Immediate requeue is implemented. Lease expiry can also move inflight messages back to ready.
Delayed retries and dead lettering are still evolving:
retry_after(..)exists in the Rust client but is not implemented end to end.- basic max-retry dead-letter behavior exists below the public surface but is incomplete.
Backpressure
Section titled “Backpressure”Delivery is pull-based. Subscriptions set bounded prefetch, so consumers do not accept unlimited inflight work.
Not a production claim
Section titled “Not a production claim”Durability is a real part of the broker and is tested. The project is still pre-alpha, and production readiness is not claimed.