When acting-pid is 'meta, take the entire delta as the delta-aggregate.

This is correct because now that we have echo-cancelled SCNs, incoming
SCNs from the metalevel are *always* new information for the contained
actors.

prospect-monolithic/examples/example-meta-echo2.rkt

@@ -0,0 +1,14 @@
+#lang prospect-monolithic
+;; The actor should receive a single event adding the (at-meta x) assertion.
+
+(require prospect/pretty)
+
+(spawn-network
+ (spawn (lambda (e counter)
+          (and e
+               (let ((new-counter (+ counter 1)))
+                 (printf "Received event ~a:\n~a\n" new-counter (prospect-pretty-print->string e))
+                 (transition (+ counter 1) '()))))
+        0
+        (list (scn/union (assertion (at-meta 'x))
+                         (subscription 'x #:meta-level 1)))))

prospect/examples/example-meta-echo2.rkt

@@ -0,0 +1,14 @@
+#lang prospect
+;; The actor should receive a single event adding the (at-meta x) assertion.
+
+(require prospect/pretty)
+
+(spawn-network
+ (spawn (lambda (e counter)
+          (and e
+               (let ((new-counter (+ counter 1)))
+                 (printf "Received event ~a:\n~a\n" new-counter (prospect-pretty-print->string e))
+                 (transition (+ counter 1) '()))))
+        0
+        (list (patch-seq (sub 'x #:meta-level 1)
+                         (assert (at-meta 'x))))))

prospect/mux.rkt

@@ -81,7 +81,7 @@
 (define (compute-patches old-m new-m label delta delta-aggregate)
   (define delta-aggregate/no-echo
     (if (meta-label? label)
-        delta-aggregate
+        delta
         (patch (trie-prune-branch (patch-added delta-aggregate) struct:at-meta)
                (trie-prune-branch (patch-removed delta-aggregate) struct:at-meta))))
   (define old-routing-table (mux-routing-table old-m))