Receives batches from the producers on other nodes and broadcasts them to this node's subscribers, one worker per pool group.

The worker joins the group's :pg group, which is how producers find it. It replies :ok to a batch only after broadcasting it locally; the producer moves that node's read cursor only on that reply.

It also remembers which producer nodes have registered with it, in an ETS table owned by the adapter supervisor so the record survives a worker restart. {:register, node, missed_writes?} sends {:cursor_expired, node} to every local topic when the producer had already flushed writes this node will not get, or when the worker already knows it (that producer lost this node's cursor). {:resume, node} only records the producer, and {:expired, node} always sends the notice.