An empty declaration is sent, so a node drops what it last held (hq 127)

push skipped any node whose declaration composed to zero resources. A
node that HELD something before — the broker opening a placement gave
an adopted node, say — then kept it forever: the empty declaration that
would drop it was never sent, and the node's own heartbeat re-applied
the stale resource with no way for the mesh to say it is gone. Now the
empty declaration is sent; the host drops what the mesh owned and keeps
what it found. A node that never held anything applies it as a no-op.
Surfaced on ace: the foundation-opening fix (#74) removed its only
resource, and the correction could not reach it until this.

cmd/mesh-controller/push_test.go

@@ -39,12 +39,14 @@ func TestOneUnresolvableNodeStillLetsTheRestBeSent(t *testing.T) {
 	}
 }
 
-// And a machine assigned nothing is neither sent nor a refusal — it is nothing to say.
-func TestAMachineAssignedNothingIsNotARefusal(t *testing.T) {
+// A machine whose declaration composes to nothing is SENT the empty declaration, not skipped
+// (novox/hq issue 127): it may have held something before, and only sending the empty
+// declaration tells it to drop what the mesh owned. It is never a refusal.
+func TestAnEmptyDeclarationIsSentSoTheNodeDropsWhatItHeld(t *testing.T) {
 	sending, refusals := composeEach([]string{"spare"},
 		func(string) (sendable, error) { return sendable{}, nil })
-	if len(sending) != 0 || len(refusals) != 0 {
-		t.Errorf("a machine assigned nothing was treated as something: %v / %v", sending, refusals)
+	if len(sending) != 1 || len(refusals) != 0 {
+		t.Errorf("an empty declaration must be sent, not skipped or refused: %v / %v", sending, refusals)
 	}
 }