Stream changes

SSE over the same safe published journal with stable per-Record ordering and exact start-now semantics as polling. Cross-Record commit order is not guaranteed; resuming an older cursor can redeliver an event. Last-Event-ID takes precedence over query cursor on reconnect. id is an opaque Change Cursor; data.event_id is deduplication identity. Named change events carry ChangeEvent JSON. checkpoint events carry a cursor when no visible event is emitted, including initial start-now checkpoint. Resume cursor expires or scope changes: before headers use HTTP 410/409; after headers send stream_error with Error JSON then close, without advancing id. Use authenticated streaming fetch/http client. See contract for checkpoint framing and resync.