chat: Move eval logic out of /lib/chat-json

This allows us to always include the bowl when evaluating a code letter.

pkg/arvo/app/chat-store.hoon

@@ -1,6 +1,6 @@
 :: chat-store: data store that holds linear sequences of chat messages
 ::
-/+  *chat-json
+/+  *chat-json, *chat-eval
 |%
 +$  move  [bone card]
 ::
@@ -193,6 +193,10 @@
   =/  mailbox=(unit mailbox)  (~(get by inbox) path.act)
   ?~  mailbox
     [~ this]
+  =*  letter  letter.envelope.act
+  =?  letter  &(?=(%code -.letter) ?=(~ output.letter))
+    =/  =hoon  (ream expression.letter)
+    letter(output (eval bol hoon))
   =:  length.config.u.mailbox  +(length.config.u.mailbox)
       number.envelope.act  length.config.u.mailbox
       envelopes.u.mailbox  (snoc envelopes.u.mailbox envelope.act)

pkg/arvo/lib/chat-json.hoon

@@ -37,10 +37,8 @@
   ?~  exp
     [~ '' ~]
   :+  ~  u.exp
-  =/  res  ((ot output+(ar dank) ~) a)
-  ?^  res
-    u.res
-  (eval:chat-eval *bowl:gall (ream u.exp))
+  ::NOTE  when sending, if output is an empty list, chat-store will evaluate
+  (fall ((ot output+(ar dank) ~) a) ~)
 ::
 ++  lett
   |=  =letter