Dead lettering

Dead lettering exists in the Stroma state layer, but it is not yet exposed as a polished public broker configuration surface.

Current state-layer behavior

Stroma can model:

• retry counts per offset
• max-retry exhaustion
• pending dead-letter state
• discard policy
• custom DLQ target topic, partition, and optional group
• durable snapshot and replay of DLQ policy and pending DLQ state

When a message reaches the retry limit, Stroma moves it to pending DLQ rather than immediately pretending it is settled. A second phase commits the DLQ action or discards the pending entry according to policy.

Custom target

The state layer can route a dead-lettered message to a custom target. DLQ copies include source metadata such as source topic and source offset in message headers.

Discard policy

For discard policy, a rejected or exhausted message is locally settled without writing a DLQ message.

Public status

The important caveat: this behavior is not yet a stable public Fibril feature.

Before the site should call dead lettering “available,” the broker needs:

• user-facing DLQ declaration or configuration
• clear retry-limit configuration
• protocol/client support where needed
• broker-level integration tests that exercise the public path