chat-view and hook: style pass and backlog truncation

pkg/arvo/app/chat-hook.hoon

@@ -400,16 +400,14 @@
   ?>  ?=(^ pax)
   =/  last  (dec (lent pax))
   =/  backlog-start=(unit @ud)
-    %+  rush
-      (snag last `(list @ta)`pax)
-    dem:ag
+    (rush (snag last `(list @ta)`pax) dem:ag)
   =/  pas  `path`(oust [last 1] `(list @ta)`pax)
   ?>  ?=([* ^] pas)
   ?>  (~(has by synced) pas)
   ::  check if read is permitted
   ?>  (is-permitted src.bol pas)
-  =/  =mailbox  (need (chat-scry pas))
-  =*  envs  envelopes.mailbox
+  =/  backlog-limit  10.000
+  =/  envs  (scag backlog-limit envelopes:(need (chat-scry pas)))
   %-  zing
   :~  [%give %fact ~ %chat-update !>([%create pas])]~
       ?.  ?&(?=(^ backlog-start) (~(has by allow-history) pas))  ~

pkg/arvo/app/chat-view.hoon

@@ -121,14 +121,7 @@
       %-  ~(run by inbox)
       |=  =mailbox
       ^-  ^mailbox
-      [config.mailbox (truncate-envelopes envelopes.mailbox)]
-    ::
-    ++  truncate-envelopes
-      |=  envelopes=(list envelope)
-      ^-  (list envelope)
-      ?:  (lth (lent envelopes) message-limit)
-        envelopes
-      (scag message-limit envelopes)
+      [config.mailbox (scag message-limit envelopes.mailbox)]
     --
   ::
   ++  on-agent