kiln: add vats-diff mark

pkg/arvo/mar/kiln/vats-diff.hoon

@@ -0,0 +1,54 @@
+/-  hood
+|_  =diff:hood
+++  grad  %noun
+++  grow
+  |%
+  ++  noun  diff
+  ++  json  
+    =,  enjs:format
+    |^
+    %+  frond  -.diff
+    ?-  -.diff
+      %block  (block +.diff)
+      ?(%merge-sunk %merge-fail)  (desk-arak-err +.diff)
+      ?(%reset %merge %suspend %revive)  (desk-arak +.diff)
+    ==
+    ::
+    ++  block
+      |=  [=desk =arak:hood =weft:hood blockers=(set desk)]
+      %+  merge  (desk-arak desk arak)
+      %-  pairs
+      :~  weft+(weft:enjs:hood weft)
+          blockers+a+(turn ~(tap in blockers) (lead %s))
+      ==
+    ::
+    ++  desk-arak
+      |=  [=desk =arak:hood]
+      %-  pairs
+      :~  desk+s+desk
+          arak+(arak:enjs:hood arak)
+      ==
+    ::
+    ++  desk-arak-err
+      |=  [=desk =arak:hood =tang]
+      %+  merge  (desk-arak desk arak)
+      %+  frond   %tang
+      a+(turn tang tank)
+    ::
+    ++  merge
+      |=  [a=^json b=^json]
+      ^-  ^json
+      ?>  &(?=(%o -.a) ?=(%o -.b))
+      o+(~(uni by p.a) p.b)
+    --
+  --
+++  grab
+  |%
+  ++  noun  diff:hood
+  --
+--
+
+      
+
+
+