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/conformance.sh

@@ -30,6 +30,7 @@ trap "rm -f $TMPFILE $OUTFILE" EXIT
 SUITES=(
   "session|id-session-test-pass|id-session-test-count"
   "token|id-token-test-pass|id-token-test-count"
+  "registry|id-registry-test-pass|id-registry-test-count"
 )
 
 cat > "$TMPFILE" << 'EPOCHS'
@@ -43,12 +44,16 @@ cat > "$TMPFILE" << 'EPOCHS'
 (load "lib/erlang/runtime.sx")
 (load "lib/identity/session.sx")
 (load "lib/identity/token.sx")
+(load "lib/identity/registry.sx")
 (load "lib/identity/tests/session.sx")
 (load "lib/identity/tests/token.sx")
+(load "lib/identity/tests/registry.sx")
 (epoch 100)
 (eval "(list id-session-test-pass id-session-test-count)")
 (epoch 101)
 (eval "(list id-token-test-pass id-token-test-count)")
+(epoch 102)
+(eval "(list id-registry-test-pass id-registry-test-count)")
 EPOCHS
 
 timeout 600 "$SX_SERVER" < "$TMPFILE" > "$OUTFILE" 2>&1

lib/identity/registry.sx

@@ -0,0 +1,22 @@
+;; identity/registry.sx — routes sessions by id and by (subject, client).
+;;
+;; The registry is the directory that makes SSO possible: one subject can
+;; hold many sessions (one per client), and the OAuth machine asks it the
+;; single question that drives silent login — \"is there a live session
+;; for this subject + this client?\". It stores (SessionId, Subject,
+;; Client, Pid) rows and answers:
+;;
+;;   whereis_session(Id)      -> {ok, Pid} | {error, not_found}
+;;   lookup(Subject, Client)  -> {ok, Pid} | {error, not_found}   (SSO probe)
+;;   sessions_for(Subject)    -> {ok, [SessionId, ...]}           (fan-out)
+;;
+;; The registry only routes — it holds no grant state and decides nothing.
+;; Liveness of the routed-to session is that session process's own affair.
+
+(define
+  identity-registry-source
+  "-module(identity_registry).\n\n   start() ->\n     spawn(fun () -> loop([]) end).\n\n   register(Reg, SessionId, Subject, Client, Pid) ->\n     Reg ! {register, SessionId, Subject, Client, Pid, self()},\n     receive {registry_reply, R} -> R end.\n\n   whereis_session(Reg, SessionId) ->\n     Reg ! {whereis_session, SessionId, self()},\n     receive {registry_reply, R} -> R end.\n\n   lookup(Reg, Subject, Client) ->\n     Reg ! {lookup, Subject, Client, self()},\n     receive {registry_reply, R} -> R end.\n\n   sessions_for(Reg, Subject) ->\n     Reg ! {sessions_for, Subject, self()},\n     receive {registry_reply, R} -> R end.\n\n   deregister(Reg, SessionId) ->\n     Reg ! {deregister, SessionId, self()},\n     receive {registry_reply, R} -> R end.\n\n   stop(Reg) ->\n     Reg ! {stop, self()},\n     receive {registry_reply, R} -> R end.\n\n   loop(Entries) ->\n     receive\n       {register, SessionId, Subject, Client, Pid, From} ->\n         From ! {registry_reply, ok},\n         loop([{SessionId, Subject, Client, Pid} | remove_id(SessionId, Entries)]);\n       {whereis_session, SessionId, From} ->\n         From ! {registry_reply, find_id(SessionId, Entries)},\n         loop(Entries);\n       {lookup, Subject, Client, From} ->\n         From ! {registry_reply, find_sc(Subject, Client, Entries)},\n         loop(Entries);\n       {sessions_for, Subject, From} ->\n         From ! {registry_reply, {ok, collect_subject(Subject, Entries)}},\n         loop(Entries);\n       {deregister, SessionId, From} ->\n         From ! {registry_reply, ok},\n         loop(remove_id(SessionId, Entries));\n       {stop, From} ->\n         From ! {registry_reply, ok}\n     end.\n\n   find_id(_, []) -> {error, not_found};\n   find_id(Id, [{Sid, _, _, Pid} | Rest]) ->\n     case Sid =:= Id of\n       true -> {ok, Pid};\n       false -> find_id(Id, Rest)\n     end.\n\n   find_sc(_, _, []) -> {error, not_found};\n   find_sc(Subject, Client, [{_, Su, Cl, Pid} | Rest]) ->\n     case Su =:= Subject of\n       true ->\n         case Cl =:= Client of\n           true -> {ok, Pid};\n           false -> find_sc(Subject, Client, Rest)\n         end;\n       false -> find_sc(Subject, Client, Rest)\n     end.\n\n   collect_subject(_, []) -> [];\n   collect_subject(Subject, [{Sid, Su, _, _} | Rest]) ->\n     case Su =:= Subject of\n       true -> [Sid | collect_subject(Subject, Rest)];\n       false -> collect_subject(Subject, Rest)\n     end.\n\n   remove_id(_, []) -> [];\n   remove_id(Id, [{Sid, Su, Cl, Pid} | Rest]) ->\n     case Sid =:= Id of\n       true -> remove_id(Id, Rest);\n       false -> [{Sid, Su, Cl, Pid} | remove_id(Id, Rest)]\n     end.")
+
+(define
+  identity-load-registry!
+  (fn () (erlang-load-module identity-registry-source)))

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"}
   ]
 }

lib/identity/scoreboard.md

@@ -1,11 +1,12 @@
 # identity-on-sx Scoreboard
 
-**Total: 20 / 20 tests passing**
+**Total: 29 / 29 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | session | 11 | 11 |
 | ✅ | token | 9 | 9 |
+| ✅ | registry | 9 | 9 |
 
 
 Generated by `lib/identity/conformance.sh`.

lib/identity/tests/registry.sx

@@ -0,0 +1,99 @@
+;; identity/tests/registry.sx — routing by id and by (subject, client),
+;; SSO fan-out (one subject, many clients), and integration with live
+;; session processes routed through the registry.
+
+(define id-registry-test-count 0)
+(define id-registry-test-pass 0)
+(define id-registry-test-fails (list))
+
+(define
+  id-registry-test
+  (fn
+    (name actual expected)
+    (set! id-registry-test-count (+ id-registry-test-count 1))
+    (if
+      (= actual expected)
+      (set! id-registry-test-pass (+ id-registry-test-pass 1))
+      (append! id-registry-test-fails {:name name :expected expected :actual actual}))))
+
+(define idr-ev erlang-eval-ast)
+(define idrnm (fn (v) (get v :name)))
+
+(identity-load-session!)
+(identity-load-registry!)
+
+;; ── whereis by session id ────────────────────────────────────────
+
+(id-registry-test
+  "registered session is found by id"
+  (idrnm
+    (idr-ev
+      "Me = self(),\n       Reg = identity_registry:start(),\n       identity_registry:register(Reg, s1, alice, web, Me),\n       case identity_registry:whereis_session(Reg, s1) of\n         {ok, _} -> found;\n         {error, _} -> missing\n       end"))
+  "found")
+
+(id-registry-test
+  "unknown session id is not_found, not a crash"
+  (idrnm
+    (idr-ev
+      "Reg = identity_registry:start(),\n       case identity_registry:whereis_session(Reg, nope) of\n         {ok, _} -> found;\n         {error, Why} -> Why\n       end"))
+  "not_found")
+
+;; ── lookup by (subject, client) — the SSO probe ──────────────────
+
+(id-registry-test
+  "lookup finds a session for subject+client"
+  (idrnm
+    (idr-ev
+      "Me = self(),\n       Reg = identity_registry:start(),\n       identity_registry:register(Reg, s1, alice, web, Me),\n       case identity_registry:lookup(Reg, alice, web) of\n         {ok, _} -> found;\n         {error, _} -> missing\n       end"))
+  "found")
+
+(id-registry-test
+  "lookup is precise: right subject, wrong client misses"
+  (idrnm
+    (idr-ev
+      "Me = self(),\n       Reg = identity_registry:start(),\n       identity_registry:register(Reg, s1, alice, web, Me),\n       case identity_registry:lookup(Reg, alice, cli) of\n         {ok, _} -> found;\n         {error, _} -> missing\n       end"))
+  "missing")
+
+;; ── SSO fan-out: one subject, many clients ───────────────────────
+
+(id-registry-test
+  "sessions_for returns all of a subject's sessions"
+  (idr-ev
+    "Me = self(),\n     Reg = identity_registry:start(),\n     identity_registry:register(Reg, s1, alice, web, Me),\n     identity_registry:register(Reg, s2, alice, cli, Me),\n     identity_registry:register(Reg, s3, bob, web, Me),\n     case identity_registry:sessions_for(Reg, alice) of\n       {ok, L} -> length(L)\n     end")
+  2)
+
+(id-registry-test
+  "sessions_for an unknown subject is empty"
+  (idr-ev
+    "Reg = identity_registry:start(),\n     case identity_registry:sessions_for(Reg, ghost) of\n       {ok, L} -> length(L)\n     end")
+  0)
+
+;; ── re-register replaces the row for that id (no duplicates) ──────
+
+(id-registry-test
+  "re-registering an id does not duplicate it"
+  (idr-ev
+    "Me = self(),\n     Reg = identity_registry:start(),\n     identity_registry:register(Reg, s1, alice, web, Me),\n     identity_registry:register(Reg, s1, alice, web, Me),\n     case identity_registry:sessions_for(Reg, alice) of\n       {ok, L} -> length(L)\n     end")
+  1)
+
+;; ── deregister removes routing ───────────────────────────────────
+
+(id-registry-test
+  "deregistered session is no longer found"
+  (idrnm
+    (idr-ev
+      "Me = self(),\n       Reg = identity_registry:start(),\n       identity_registry:register(Reg, s1, alice, web, Me),\n       identity_registry:deregister(Reg, s1),\n       case identity_registry:whereis_session(Reg, s1) of\n         {ok, _} -> found;\n         {error, _} -> missing\n       end"))
+  "missing")
+
+;; ── integration: route to a live session and look it up ──────────
+
+(id-registry-test
+  "routed-to session answers lookup as active"
+  (idrnm
+    (idr-ev
+      "Me = self(),\n       Reg = identity_registry:start(),\n       S = identity_session:start(s1, alice, web, Me, infinity),\n       identity_registry:register(Reg, s1, alice, web, S),\n       {ok, Pid} = identity_registry:lookup(Reg, alice, web),\n       case identity_session:lookup(Pid) of\n         {ok, {_,_,_,St}} -> St;\n         {error, St} -> St\n       end"))
+  "active")
+
+(define
+  id-registry-test-summary
+  (str "registry " id-registry-test-pass "/" id-registry-test-count))

plans/identity-on-sx.md

@@ -19,7 +19,7 @@ through the event log, all authorization questions delegated to `acl-on-sx`.
 
 ## Status (rolling)
 
-`bash lib/identity/conformance.sh` → **20/20** (Phase 1: session, token)
+`bash lib/identity/conformance.sh` → **29/29** (Phase 1: session, token, registry)
 
 ## Ground rules
 
@@ -59,7 +59,7 @@ lib/identity/api.sx ── (identity/login) (identity/grant?) (identity/revoke)
 ## Phase 1 — Sessions + tokens
 - [x] `session.sx` — session process, create/lookup/expire
 - [x] `token.sx` — issue/introspect/revoke (opaque, grant-backed)
-- [ ] `registry.sx` — route by subject/client
+- [x] `registry.sx` — route by subject/client
 - [ ] `api.sx` + tests + scoreboard + conformance.sh
 
 ## Phase 2 — OAuth2 flows
@@ -78,6 +78,11 @@ lib/identity/api.sx ── (identity/login) (identity/grant?) (identity/revoke)
 - [ ] tests: audit completeness, cross-instance subject mapping
 
 ## Progress log
+- 2026-06-06 — `registry.sx`: directory process routing sessions by id and
+  by (subject, client). Answers the SSO probe `lookup(Subject, Client)` and
+  the fan-out `sessions_for(Subject)` (one subject, many clients). Routes
+  only — holds no grant state. Integration-tested end-to-end: register a live
+  session, route to it, confirm it answers active. +9 → 29/29.
 - 2026-06-06 — `token.sx`: opaque grant-backed tokens. Token = `make_ref`
   (carries no info); the token table is a process; `introspect` is a live
   lookup every time so revocation is real (RFC 7009) — a revoked token reads