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When leader consumer detects a change of topic metadata, it should currently be the only case when it wants to trigger a group rebalance. We will explicitly set the JoinReason to `topic_metadata_change` so that group coordinator will proceed to rebalance stage. If there is no member protocol change and JoinReason is `Blind`, then we shall not rebalance on known member rejoin. For dynamic members (members rejoin with UNKNOWN_MEMBER_ID) this should have no effect because we only check join reason when the member is joining with an identity. For static members, if the JoinReason is specified as `blind`, stable group won't trigger rebalance since this indicates a restart happen on this member and nothing should be affected for the entire group.

Be aware that JoinReason takes lower priority than the current rebalance logic checking such as protocol change monitoringor unknown member join.

Compatibility, Deprecation, and Migration Plan

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