Message deduplication has unit tests in MessageDeduplicator but no integration test verifying the full pipeline: client sends duplicate messages -> server drops them at partition level.

What to focus on:

• Enable deduplication via server config (system.message_deduplication.enabled = true)
• Send messages with explicit IDs, then resend the same IDs
• Poll and verify only unique messages were persisted
• Test TTL expiry: after expiry window, previously seen IDs should be accepted again

Files to reference:

• core/common/src/deduplication/message_deduplicator.rs - core dedup logic + existing unit tests
• core/common/src/types/message/messages_batch_mut.rs - prepare_for_persistence() dedup integration
• core/server/src/streaming/partitions/helpers.rs - create_message_deduplicator() from config
• core/integration/tests/server/scenarios/ - existing server scenario tests for pattern reference

Related (closed):

• Write testcase to verify deduplication of messages #92 - closed when unit tests were added, no integration coverage
• Message deduplication should have limited time window #207 - TTL + max_entries config, implemented

Done when an integration test proves that duplicate messages are dropped end-to-end with deduplication enabled, and unique messages pass through.