observe-hook + thread: remove metadata when leaving a group

pkg/arvo/app/observe-hook.hoon

@@ -11,11 +11,13 @@
 +$  versioned-state
   $%  state-0
       state-1
+      state-2
   ==
 ::
 +$  serial   @uv
 +$  state-0  [%0 observers=(map serial observer:sur)]
 +$  state-1  [%1 observers=(map serial observer:sur)]
++$  state-1  [%2 observers=(map serial observer:sur)]
 ::
 ++  got-by-val
   |=  [a=(map serial observer:sur) b=observer:sur]
@@ -27,7 +29,7 @@
 --
 ::
 %-  agent:dbug
-=|  state-1
+=|  state-2
 =*  state  -
 ::
 ^-  agent:gall
@@ -67,7 +69,14 @@
   ^-  (quip card _this)
   =/  old-state  !<(versioned-state old-vase)
   ?-  -.old-state
-    %1  `this(state old-state)
+    %2  `this(state old-state)
+  ::
+      %1
+    =.  state  [%2 observers.old-state]
+    %+  on-poke
+      %observe-action
+    !>  ^-  action:sur
+    [%watch %group-store /groups %group-leave-metadata]
   ::
       %0
     =.  state  [%1 observers.old-state]

pkg/arvo/ted/group/leave-metadata.hoon

@@ -0,0 +1,43 @@
+/-  spider, grp=group-store, met=metadata-store, hook=metadata-hook
+/+  strandio, res=resource
+::
+=*  strand    strand:spider
+=*  raw-poke  raw-poke:strandio
+=*  scry      scry:strandio
+::
+^-  thread:spider
+|=  arg=vase
+=/  m  (strand ,vase)
+^-  form:m
+=+  !<([=update:grp ~] arg)
+?.  ?=(%remove-group -.update)
+  (pure:m !>(~))
+;<  =bowl:spider  bind:m  get-bowl:strandio
+;<  ~  bind:m
+  %+  raw-poke
+    [our.bowl %metadata-hook]
+  :-  %metadata-hook-action
+  !>  ^-  metadata-hook-action:hook
+  [%remove (en-path:res resource.update)]
+::
+::  get metadata associated with group and remove it
+;<  =associations:met  bind:m
+  %+  scry  associations:met
+  ;:  weld
+    /gx/metadata-store/group
+    (en-path:res resource.update)
+    /noun
+  ==
+=/  entries=(list [g=group-path:met m=md-resource:met])
+  ~(tap in ~(key by associations))
+|-  ^-  form:m
+=*  loop  $
+?~  entries
+  (pure:m !>(~))
+;<  ~  bind:m
+  %+  raw-poke
+    [our.bowl %metadata-store]
+  :-  %metadata-action
+  !>  ^-  metadata-action:met
+  [%remove g.i.entries m.i.entries]
+loop(entries t.entries)