handle un-tombstoning

bgs/bgs.go

@@ -777,6 +777,33 @@ func (bgs *BGS) handleFedEvent(ctx context.Context, host *models.PDS, env *event
 			return fmt.Errorf("rebase was true in event seq:%d,host:%s", evt.Seq, host.Host)
 		}
 
+		if host.ID != u.PDS {
+			log.Infow("received event for repo from different pds than expected", "repo", evt.Repo, "expPds", u.PDS, "gotPds", host.Host)
+			subj, err := bgs.createExternalUser(ctx, evt.Repo)
+			if err != nil {
+				return err
+			}
+
+			if subj.PDS != host.ID {
+				return fmt.Errorf("event from non-authoritative pds")
+			}
+		}
+
+		if u.Tombstoned {
+			// we've checked the authority of the users PDS, so reinstate the account
+			if err := bgs.db.Model(&User{}).Where("id = ?", u.ID).UpdateColumn("tombstoned", false).Error; err != nil {
+				return fmt.Errorf("failed to un-tombstone a user: %w", err)
+			}
+
+			ai, err := bgs.Index.LookupUser(ctx, u.ID)
+			if err != nil {
+				return fmt.Errorf("failed to look up user (tombstone recover): %w", err)
+			}
+
+			// Now a simple re-crawl should suffice to bring the user back online
+			return bgs.Index.Crawler.AddToCatchupQueue(ctx, host, ai, evt)
+		}
+
 		// skip the fast path for rebases or if the user is already in the slow path
 		if bgs.Index.Crawler.RepoInSlowPath(ctx, host, u.ID) {
 			rebasesCounter.WithLabelValues(host.Host).Add(1)
@@ -1050,6 +1077,7 @@ func (s *BGS) createExternalUser(ctx context.Context, did string) (*models.Actor
 				return nil, fmt.Errorf("failed to update users pds: %w", err)
 			}
 
+			exu.PDS = peering.ID
 		}
 
 		if exu.Handle.String != handle {