===== Duplicate Detection =====

Duplicate detection prevents reprocessing of frames that have already been handled.

Responsibilities include:

Tracking recently seen (source, message_id) pairs
Rejecting duplicate frames
Supporting idempotent message handling

This is especially important in:

Retransmission scenarios
Multi-hop or bridged networks

Implementations should use a bounded, memory-efficient cache (e.g., ring buffer or LRU).