identity: session registry — route by id and (subject, client) + SSO fan-out (9 tests)

Directory process holding (SessionId, Subject, Client, Pid) rows. Answers
the SSO probe lookup(Subject, Client) and the fan-out sessions_for(Subject)
(one subject, many clients). Routes only — no grant state, decides nothing.
Integration-tested: register a live session, route to it, confirm active.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/identity/scoreboard.json

@@ -1,9 +1,10 @@
 {
   "language": "identity",
-  "total_pass": 20,
-  "total": 20,
+  "total_pass": 29,
+  "total": 29,
   "suites": [
     {"name":"session","pass":11,"total":11,"status":"ok"},
-    {"name":"token","pass":9,"total":9,"status":"ok"}
+    {"name":"token","pass":9,"total":9,"status":"ok"},
+    {"name":"registry","pass":9,"total":9,"status":"ok"}
   ]
 }