feat(membership): room discovery — GET /members/{endpoint}/rooms + ListMyRooms

A peer invited to an encrypted room needs to find it: the control plane is
pull-based (no server push of invitations), so add a discovery endpoint that
lists every room an endpoint belongs to, with the room's metadata and the
endpoint's role.

- store.ListRoomsForEndpoint: JOIN members+rooms, ordered by room id, empty
  slice (not error) for an endpoint in no rooms.
- membershipd: GET /members/{endpoint}/rooms returns {room_id, subject, epoch,
  policy, role}[].
- client.ListMyRooms + RoomRef: a bot polls this to discover and then Join +
  Subscribe rooms it was invited to.

Tests: store-level (owner in N rooms, member in one, unknown endpoint → []) and
client-level e2e through the embedded harness (B discovers a room A invited it
to, without prior knowledge of the room id; owner sees role=owner).

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

pkg/membership/server.go

@@ -45,6 +45,7 @@ func (s *Server) routes() {
 	s.mux.HandleFunc("POST /rooms/{id}/invite", s.handleInvite)
 	s.mux.HandleFunc("GET /rooms/{id}/key", s.handleGetKey)
 	s.mux.HandleFunc("GET /rooms/{id}/members", s.handleListMembers)
+	s.mux.HandleFunc("GET /members/{endpoint}/rooms", s.handleListMemberRooms)
 	s.mux.HandleFunc("POST /rooms/{id}/rekey", s.handleRekey)
 	s.mux.HandleFunc("GET /rooms/{id}", s.handleGetRoom)
 	s.mux.HandleFunc("POST /blobs", s.handlePutBlob)
@@ -101,6 +102,14 @@ type roomResp struct {
 	Policy  policyJSON `json:"policy"`
 }
 
+type memberRoomJSON struct {
+	RoomID  string     `json:"room_id"`
+	Subject string     `json:"subject"`
+	Epoch   int        `json:"epoch"`
+	Policy  policyJSON `json:"policy"`
+	Role    string     `json:"role"`
+}
+
 type rekeyKey struct {
 	Endpoint  string `json:"endpoint"`
 	SealedKey []byte `json:"sealed_key"`
@@ -262,6 +271,30 @@ func (s *Server) handleListMembers(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, out)
 }
 
+func (s *Server) handleListMemberRooms(w http.ResponseWriter, r *http.Request) {
+	endpoint := r.PathValue("endpoint")
+	if endpoint == "" {
+		writeErr(w, http.StatusBadRequest, "endpoint required")
+		return
+	}
+	rooms, err := s.store.ListRoomsForEndpoint(endpoint)
+	if err != nil {
+		writeErr(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	out := make([]memberRoomJSON, 0, len(rooms))
+	for _, rm := range rooms {
+		out = append(out, memberRoomJSON{
+			RoomID:  rm.RoomID,
+			Subject: rm.Subject,
+			Epoch:   rm.Epoch,
+			Policy:  policyJSON{Encrypt: rm.Encrypt, Persist: rm.Persist, SignMsgs: rm.SignMsgs},
+			Role:    rm.Role,
+		})
+	}
+	writeJSON(w, http.StatusOK, out)
+}
+
 func (s *Server) handleGetRoom(w http.ResponseWriter, r *http.Request) {
 	roomID := r.PathValue("id")
 	info, err := s.store.GetRoom(roomID)

pkg/membership/store.go

@@ -219,6 +219,42 @@ func (s *Store) ListMembers(roomID string) ([]Member, error) {
 	return out, rows.Err()
 }
 
+// RoomMembership is a room an endpoint belongs to, with that endpoint's role.
+// It is the per-endpoint view used for room discovery (a peer asking "which
+// rooms am I in?") so a freshly-invited member can find and join its rooms.
+type RoomMembership struct {
+	RoomInfo
+	Role string
+}
+
+// ListRoomsForEndpoint returns every room the given endpoint is a member of,
+// with the room's current metadata and the endpoint's role, ordered by room id.
+// An endpoint that is in no rooms yields an empty slice (not an error).
+func (s *Store) ListRoomsForEndpoint(endpoint string) ([]RoomMembership, error) {
+	rows, err := s.db.Query(
+		`SELECT r.room_id, r.subject, r.key_epoch, r.encrypt, r.persist, r.sign_msgs, r.owner_endpoint, m.role
+		 FROM members m JOIN rooms r ON r.room_id = m.room_id
+		 WHERE m.endpoint = ? ORDER BY r.room_id`,
+		endpoint,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("membership: list rooms for endpoint %q: %w", endpoint, err)
+	}
+	defer rows.Close()
+
+	var out []RoomMembership
+	for rows.Next() {
+		var rm RoomMembership
+		var enc, per, sgn int
+		if err := rows.Scan(&rm.RoomID, &rm.Subject, &rm.Epoch, &enc, &per, &sgn, &rm.OwnerEndpoint, &rm.Role); err != nil {
+			return nil, fmt.Errorf("membership: scan room membership: %w", err)
+		}
+		rm.Encrypt, rm.Persist, rm.SignMsgs = enc != 0, per != 0, sgn != 0
+		out = append(out, rm)
+	}
+	return out, rows.Err()
+}
+
 // GetSealedKey returns the sealed room key for an endpoint at a given epoch.
 // If epoch <= 0, the latest epoch for that endpoint is returned.
 func (s *Store) GetSealedKey(roomID, endpoint string, epoch int) (int, []byte, error) {

pkg/membership/store_test.go

@@ -35,6 +35,58 @@ func TestMigrationsCreateSchema(t *testing.T) {
 	}
 }
 
+func TestListRoomsForEndpoint(t *testing.T) {
+	s := openTestStore(t)
+
+	// Owner of two rooms; a member in only the first.
+	owner, member := "owner-ep", "member-ep"
+	mk := func(id, subj string) RoomInfo {
+		return RoomInfo{RoomID: id, Subject: subj, Encrypt: true, Persist: true, SignMsgs: true, OwnerEndpoint: owner}
+	}
+	if err := s.CreateRoom(mk("room-a", "room.a"), []byte("os"), []byte("ok"), []byte("k")); err != nil {
+		t.Fatalf("CreateRoom a: %v", err)
+	}
+	if err := s.CreateRoom(mk("room-b", "room.b"), []byte("os"), []byte("ok"), []byte("k")); err != nil {
+		t.Fatalf("CreateRoom b: %v", err)
+	}
+	if err := s.AddMember("room-a", Member{Endpoint: member, Role: "member", SignPub: []byte("s"), KexPub: []byte("k")}, 1, []byte("mk")); err != nil {
+		t.Fatalf("AddMember: %v", err)
+	}
+
+	// Owner is in both rooms, as owner, ordered by room id.
+	ownerRooms, err := s.ListRoomsForEndpoint(owner)
+	if err != nil {
+		t.Fatalf("ListRoomsForEndpoint owner: %v", err)
+	}
+	if len(ownerRooms) != 2 {
+		t.Fatalf("owner: expected 2 rooms, got %d", len(ownerRooms))
+	}
+	if ownerRooms[0].RoomID != "room-a" || ownerRooms[1].RoomID != "room-b" {
+		t.Fatalf("owner rooms not ordered: %+v", ownerRooms)
+	}
+	if ownerRooms[0].Role != "owner" || !ownerRooms[0].Encrypt || ownerRooms[0].Subject != "room.a" {
+		t.Fatalf("owner room metadata wrong: %+v", ownerRooms[0])
+	}
+
+	// Member is in exactly one room, as member.
+	memberRooms, err := s.ListRoomsForEndpoint(member)
+	if err != nil {
+		t.Fatalf("ListRoomsForEndpoint member: %v", err)
+	}
+	if len(memberRooms) != 1 || memberRooms[0].RoomID != "room-a" || memberRooms[0].Role != "member" {
+		t.Fatalf("member rooms wrong: %+v", memberRooms)
+	}
+
+	// An unknown endpoint yields an empty slice, not an error.
+	none, err := s.ListRoomsForEndpoint("nobody")
+	if err != nil {
+		t.Fatalf("ListRoomsForEndpoint nobody: %v", err)
+	}
+	if len(none) != 0 {
+		t.Fatalf("expected no rooms for unknown endpoint, got %+v", none)
+	}
+}
+
 func TestRoomMemberKeyRoundTrip(t *testing.T) {
 	s := openTestStore(t)