Cope with add-role after kill of a process

os2.rkt

@@ -251,6 +251,8 @@
     [(kill pid-to-kill reason) (do-kill (or pid-to-kill pid) reason state)]))
 
 (define (do-subscribe pid topic hs k state)
+  (cond
+   [(hash-has-key? (vm-processes state) pid)
     (define old-process (hash-ref (vm-processes state) pid))
     (define eid-number (process-next-eid-number old-process))
     (define new-eid (list pid eid-number))
@@ -289,7 +291,8 @@
 				      new-eid
 				      (endpoint new-eid
 						topic
-					      hs))]))
+						hs))])]
+   [else state]))
 
 (define (do-unsubscribe pid eid reason state)
   (cond