feat: add worker retry and replay safety

README.md

@@ -81,6 +81,11 @@ worker processing is not connected yet.
 * Flush on 1,000 records or 2-second timeout
 * Kafka offsets committed only after successful ClickHouse batch writes
 * Remaining worker buffer flushed during graceful shutdown
+* ClickHouse insert retries with exponential backoff
+* Failed ClickHouse batches routed to the DLQ after three attempts
+* Whole-batch offset commits with no partial Kafka acknowledgement
+* Replay-safe storage using deterministic UUIDv5 identifiers and `ReplacingMergeTree`
+* Graceful worker shutdown flushes buffered records before exit
 
 ## Project Structure
 
@@ -205,3 +210,11 @@ pytest -v
 ```
 
 The current test suite covers domain validation, normalization, deterministic ID generation, and API request validation.
+
+## Delivery Semantics
+
+The worker uses at-least-once delivery.
+
+Kafka offsets are committed only after a ClickHouse batch is successfully written or, after exhausted retries, the complete failed batch is acknowledged by the DLQ.
+
+Repeated records use deterministic UUIDv5 identifiers and `ReplacingMergeTree` to support replay-safe storage.