diff --git a/examples/operational-transformation/syndicate-server.rkt b/examples/operational-transformation/syndicate-server.rkt
index dd1ff0a..ddf1246 100644
--- a/examples/operational-transformation/syndicate-server.rkt
+++ b/examples/operational-transformation/syndicate-server.rkt
@@ -11,6 +11,7 @@
 (struct file-being-edited (name) #:prefab)
 (struct proposed-op (p) #:prefab)
 (struct accepted-op (p) #:prefab)
+(struct client-seen-up-to (revision) #:prefab)
 
 (define cmdline-port (make-parameter 5888))
 (define cmdline-filename (make-parameter "info.rkt"))
@@ -23,6 +24,17 @@
                                                      ""))))])
               (assert (extract-snapshot (state)))
 
+              (define/query-set client-seen-revs (client-seen-up-to $rev) rev)
+              (let ((oldest-needed-rev #f))
+                (begin/dataflow
+                  (define min-rev
+                    (or (for/fold [(min-rev #f)] [(rev (client-seen-revs))]
+                          (min (or min-rev rev) rev))
+                        (server-state-revision (state))))
+                  (when (not (equal? oldest-needed-rev min-rev))
+                    (set! oldest-needed-rev min-rev)
+                    (state (forget-operation-history (state) oldest-needed-rev)))))
+
               (begin/dataflow
                 (display-to-file (simple-document-text (server-state-document (state)))
                                  (cmdline-filename)
@@ -50,15 +62,21 @@
     (newline p)
     (send! (tcp-channel s c (get-output-bytes p))))
 
+  (field [seen-up-to 0])
+  (assert (client-seen-up-to (seen-up-to)))
+
   (on-start
    (output filename)
    (let-event [(asserted ($ snapshot (server-snapshot _ _)))]
               (output snapshot)
+              (seen-up-to (server-snapshot-revision snapshot))
               (react (on (message (accepted-op $p))
                          (output p)))))
 
   (on (message (tcp-channel-line c s $line))
-      (send! (proposed-op (deserialize (read (open-input-bytes line)))))))
+      (match (deserialize (read (open-input-bytes line)))
+        [(? number? n) (seen-up-to n)]
+        [(? pending-operation? p) (send! (proposed-op p))])))
 
 (module+ main
   (require racket/cmdline)