pageserver: return correct LSN for interpreted proto keep alive responses (#9928)

## Problem

For the interpreted proto the pageserver is not returning the correct
LSN
in replies to keep alive requests. This is because the interpreted
protocol arm
was not updating `last_rec_lsn`.

## Summary of changes

* Return correct LSN in keep-alive responses
* Fix shard field in wal sender traces

pageserver/src/tenant/timeline/walreceiver/walreceiver_connection.rs

@@ -454,6 +454,10 @@ pub(super) async fn handle_walreceiver_connection(
                     timeline.get_last_record_lsn()
                 );
 
+                if let Some(lsn) = next_record_lsn {
+                    last_rec_lsn = lsn;
+                }
+
                 Some(streaming_lsn)
             }
 

safekeeper/src/handler.rs

@@ -212,8 +212,9 @@ impl<IO: AsyncRead + AsyncWrite + Unpin + Send> postgres_backend::Handler<IO>
                 );
 
             if let Some(shard) = self.shard.as_ref() {
-                tracing::Span::current()
-                    .record("shard", tracing::field::display(shard.shard_slug()));
+                if let Some(slug) = shard.shard_slug().strip_prefix("-") {
+                    tracing::Span::current().record("shard", tracing::field::display(slug));
+                }
             }
 
             Ok(())

safekeeper/src/wal_service.rs

@@ -44,7 +44,7 @@ pub async fn task_main(
                     error!("connection handler exited: {}", err);
                 }
             }
-            .instrument(info_span!("", cid = %conn_id, ttid = field::Empty, application_name = field::Empty)),
+            .instrument(info_span!("", cid = %conn_id, ttid = field::Empty, application_name = field::Empty, shard = field::Empty)),
         );
     }
 }