Ensure that mentions appear in cc

posts.py

@@ -898,6 +898,16 @@ def createPostBase(baseDir: str, nickname: str, domain: str, port: int,
     if eventUUID:
         postObjectType = 'Event'
 
+    # public posts with mentions should include the mentioned
+    # actors within CC
+    # "I think we don’t notify about mentions unless the person
+    #  is also addressed in to/cc" -- gargron
+    if toRecipients and toCC and mentionedRecipients:
+        if len(toRecipients) == 1 and len(toCC) == 1:
+            if toRecipients[0].endswith('#Public') and \
+               toCC[0].endswith('/followers'):
+                toCC += mentionedRecipients
+
     if not clientToServer:
         actorUrl = httpPrefix + '://' + domain + '/users/' + nickname