Module dlq 

Dead Letter Queue — FR-004

Persistent DLQ for failed/undeliverable messages:

• Messages that fail processing N times → routed to DLQ
• DLQ stored in memory (can be persisted via checkpoint)
• Replay API: re-inject messages to specified destination
• Per-actor DLQ configuration (max retries, TTL)
• DLQ metrics: depth, ingress rate, age distribution

Structs

DeadLetter

A message in the dead letter queue with metadata.

DeadLetterQueue

Dead letter queue.

DlqConfig

Configuration for dead letter queue behavior.

DlqMetrics

DLQ metrics snapshot.

Enums

DeadLetterReason

Reason a message was sent to the dead letter queue.