Fix a design flaw in Syndicate-HLL for syndicate/rkt.

If:
 - a field is used in an assertion of interest in facet A
 - and that field changes
 - to a value that causes the assertion of interest to overlap
   with some facet B's assertion of interest
 - and an assertion matching that interest was already known to the actor,
Then:
 - previously, facet A would not be informed of the matching assertion
 - but now, it is informed of the matching assertion.

This more or less only affects "on asserted" endpoints.

The change here should be written up as an erratum to chapter 5 in my
dissertation. Also, syndicate/js needs to be checked for the bug and
probably fixed in an analogous way.

racket/syndicate/actor.rkt

@@ -1171,8 +1171,18 @@
                                (with-current-facet fid #f
                                  (define ep (hash-ref (facet-endpoints f) eid))
                                  (define new-patch ((endpoint-patch-fn ep)))
-                                 (update-stream! eid (compose-patch new-patch
-                                                                    (core:retract ?))))))))
+                                 (define a (current-actor-state))
+                                 (define new-interests
+                                   (trie-subtract (patch-added new-patch)
+                                                  (mux-interests-of (actor-state-mux a) eid)
+                                                  #:combiner (lambda (v1 v2) trie-empty)))
+                                 (define newly-relevant-knowledge
+                                   (biased-intersection (actor-state-knowledge a) new-interests))
+                                 (update-stream! eid (compose-patch new-patch (core:retract ?)))
+                                 (facet-handle-event! fid
+                                                      (lookup-facet fid)
+                                                      (patch newly-relevant-knowledge trie-empty)
+                                                      #t))))))
 
 (define (update-stream! eid patch)
   (define a (current-actor-state))

racket/syndicate/examples/actor/example-synthetic-patch-2.rkt

@@ -1,7 +1,7 @@
 #lang syndicate
-;; Illustrates a bug where an endpoint whose interest moves with time,
-;; where that interest eventually overlaps with existing interest,
-;; fails to be notified of an otherwise-known assertion.
+;; Illustrates a (fixed) bug where an endpoint whose interest moves
+;; with time, where that interest eventually overlaps with existing
+;; interest, fails to be notified of an otherwise-known assertion.
 ;;
 ;; Symptomatic output:
 ;;