Merge branch 'm/clay-u' (#2119)

* origin/m/clay-u:
  clay: implement %u care

Signed-off-by: Jared Tobin <jared@tlon.io>

bin/solid.pill

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:af2f4933ed032948f40dd6cc748743294e4cd8f402ed232f61d5357e754fcb8f
-size 9644935
+oid sha256:c5c7e56d73a3cd15c70b4cd3877da03808e4383097b47c7050f30d0160830e1b
+size 9645556

pkg/arvo/sys/vane/clay.hoon

@@ -3890,12 +3890,18 @@
     ::  at any of its children.
     ::
     ++  read-u
-      |=  {yon/aeon pax/path}
-      ^-  (unit (unit (each {$null (hypo ~)} lobe)))
-      =+  tak=(~(get by hit.dom) yon)
-      ?~  tak
+      |=  [yon=aeon pax=path]
+      ^-  (unit (unit (each [%flag (hypo ?)] lobe)))
+      ::  if asked for a future version, we don't have an answer
+      ::
+      ?~  tak=(~(get by hit.dom) yon)
         ~
-      ``[%& %null [%atom %n ~] ~]
+      ::  look up the yaki snapshot based on the version
+      ::
+      =/  yak=yaki  (tako-to-yaki u.tak)
+      ::  produce the result based on whether or not there's a file at :pax
+      ::
+      ``[%& %flag -:!>(*?) (~(has by q.yak) pax)]
     ::
     ::  Gets the dome (desk state) at a particular aeon.
     ::