Actors lineages share a handle allocator

For multiple actors to communicate through the same relay they
must use unique assertion handles.

src/syndicate/actors.nim

@@ -43,7 +43,9 @@ type
     future: Future[void]
     name: string
     id: ActorId
-    handleAllocator: Handle
+    handleAllocator: ref Handle
+      # a fresh actor gets a new ref Handle and
+      # all actors spawned from it get the same ref.
     root: Facet
     exitReason: ref Exception
     exitHooks: seq[TurnAction]
@@ -119,8 +121,8 @@ proc hash*(facet): Hash =
 proc hash*(r: Ref): Hash = !$(r.relay.hash !& r.target.unsafeAddr.hash)
 
 proc nextHandle(facet: Facet): Handle =
-  inc facet.actor.handleAllocator
-  facet.actor.handleAllocator
+  result = succ(facet.actor.handleAllocator[])
+  facet.actor.handleAllocator[] = result
 
 proc facet*(turn: var Turn): Facet = turn.facet
 
@@ -382,6 +384,7 @@ proc newActor(name: string; bootProc: TurnAction; initialAssertions: OutboundTab
   result = Actor(
     name: name,
     id: ActorId(seed))
+  new result.handleAllocator
   result.root = newFacet(result, none Facet)
   result.future = newFuture[void]($result)
   run(
@@ -397,7 +400,8 @@ proc spawn*(name: string; turn: var Turn; bootProc: TurnAction; initialAssertion
     var newOutBound: Table[Handle, OutboundAssertion]
     for key in initialAssertions:
       discard turn.facet.outbound.pop(key, newOutbound[key])
-    discard newActor(name, bootProc, newOutBound)
+    let actor = newActor(name, bootProc, newOutBound)
+    actor.handleAllocator = turn.facet.actor.handleAllocator
 
 proc newInertRef*(): Ref =
   let a = bootActor("inert") do (turn: var Turn): turn.stop()