Function stream_ws_peek_rows 

async fn stream_ws_peek_rows(
    ws: &mut WebSocket,
    client: &mut SessionClient,
    desc: &RelationDesc,
    rows_stream: &mut RecordFirstRowStream,
    max_result_size: usize,
) -> Result<(bool, Vec<WebSocketResponse>, Option<(StatementEndedExecutionReason, ExecuteContextGuard)>), Error>

Streams a peek (SELECT) result to a WebSocket client one stash batch at a time, flushing between batches so a slow client applies real backpressure and only one batch is resident. This gives a large SELECT over WebSocket the same bounded memory profile as pgwire SELECT, and mirrors the Subscribe arm of WebSocket::add_result.

On success returns the (is_err, msgs, stmt_logging) triple that add_result folds into its response. An Err means a write to the socket failed, so the server should disconnect. add_result turns that into a cancellation to match pgwire.

The Rows descriptor is sent lazily, right before the first batch of rows or an empty successful result, but never before an error. So a query that fails before producing any rows emits only an Error.