KIP-1364 — Expose Rebalance Cause to RebalanceConsumer and Metrics

Discussion ConsumerMetricsProtocol

Adds a `RebalanceCause` enum surfaced through a new accessor on the KIP-1306 `RebalanceConsumer` callback plus a cause dimension on client and coordinator rebalance metrics, carried on the wire as an `AssignmentCauses` bitmask. Existing rebalance metrics report only frequency and latency, so a spike in `rebalance-rate-per-hour` cannot be attributed to poll-interval expiry, member fencing, subscription changes, or coordinator-initiated events without grepping consumer logs.

Protocol Impact

Heartbeat · ConsumerGroupHeartbeat

Details