feat(membership,client): HTTP admin-only users API

Close the last control-plane asymmetry: rooms had a signed HTTP surface
but users were only manageable via the local CLI or direct store access.
Add admin-only HTTP endpoints, symmetric with rooms, executed against the
same privileged store the server already serves (SQLite single-node, the
replicated JetStream KV in cluster) — no new KV connection, no internal
identity, so the admin panel can manage the allowlist by signing as an
admin instead of needing --db / direct KV access.

Endpoints (all behind requireAdmin, on top of the existing
signature+nonce+TLS+enforce middleware):
  - GET  /users                    list the full allowlist (incl. revoked)
  - POST /users                    add {sign_pub, handle, role}
  - POST /users/{signpub}/revoke   revoke (status flip, no hard delete)

requireAdmin is default-deny with no dev relaxation: it allows a request
only when the authenticated signer is confirmed by the store as an active
admin; any other case (no signer, non-admin, revoked, store error) is 403,
fail-closed. The request context now also carries the signer's sign_pub
hex, because the endpoint id is a one-way hash of the key and cannot be
reversed to look the signer up in the allowlist.

Validation/idempotency mirror the CLL: sign_pub must be 64-hex, role must
be admin|member (empty defaults to member), re-adding an existing key is a
409 that leaves the row untouched. The hex check is unified into
membership.ValidateSignPubHex, reused by the CLI and the handlers.

pkg/client gains ListUsers/AddUser/RevokeUser (flat UserInfo type) signed
via doJSON, so the panel plugs in directly.

Tests: non-admin -> 403 on all three endpoints; admin add->list->revoke
roundtrip; validation (400 hex, 400 role, 409 re-add, row untouched); plus
a client test against an embedded membershipd under enforce.

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

cmd/membershipd/users_cli.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"encoding/hex"
 	"errors"
 	"flag"
 	"fmt"
@@ -90,16 +89,10 @@ func openStore(path string) membership.Store {
 
 // validateSignPubHex ensures the key is exactly a 32-byte Ed25519 public key in
 // hex (64 hex chars). Catching this here turns a silent "authorized nobody" into
-// an explicit error at seed time.
+// an explicit error at seed time. It delegates to membership.ValidateSignPubHex
+// so the CLI and the HTTP user-management handlers share one rule.
 func validateSignPubHex(signPub string) error {
-	b, err := hex.DecodeString(signPub)
-	if err != nil {
-		return fmt.Errorf("sign-pub is not valid hex: %w", err)
-	}
-	if len(b) != 32 {
-		return fmt.Errorf("sign-pub must be a 32-byte Ed25519 public key (64 hex chars), got %d bytes", len(b))
-	}
-	return nil
+	return membership.ValidateSignPubHex(signPub)
 }
 
 // kvFlags holds the connection flags shared by the --store kv path of the user

pkg/client/client.go

@@ -456,6 +456,23 @@ type memberRoomJSON struct {
 	Role    string     `json:"role"`
 }
 
+// userJSON mirrors the server's wire type on the admin user-management endpoints.
+type userJSON struct {
+	SignPub   string `json:"sign_pub"`
+	Handle    string `json:"handle"`
+	Role      string `json:"role"`
+	Status    string `json:"status"`
+	CreatedAt string `json:"created_at"`
+	RevokedAt string `json:"revoked_at,omitempty"`
+}
+
+// addUserReq is the POST /users body (mirror of the server type).
+type addUserReq struct {
+	SignPub string `json:"sign_pub"`
+	Handle  string `json:"handle"`
+	Role    string `json:"role"`
+}
+
 // ---- room operations ------------------------------------------------------
 
 // RoomRef is a room this peer belongs to, returned by ListMyRooms. It is the
@@ -490,6 +507,59 @@ func (c *Client) ListMyRooms() ([]RoomRef, error) {
 	return out, nil
 }
 
+// ---- user administration (admin-only) ------------------------------------
+
+// UserInfo is a bus user as returned by the admin user-management endpoints. It
+// is a flat view (no nested types) for the admin panel: the signing key
+// (lowercase hex), handle, role ("admin"|"member"), status ("active"|"revoked"),
+// and timestamps. RevokedAt is empty for an active user.
+type UserInfo struct {
+	SignPub   string
+	Handle    string
+	Role      string
+	Status    string
+	CreatedAt string
+	RevokedAt string
+}
+
+// ListUsers returns the full bus allowlist, including revoked users. The caller
+// must be signing as an admin: a non-admin signer is rejected by the server with
+// 403, surfaced here as an error.
+func (c *Client) ListUsers() ([]UserInfo, error) {
+	var resp []userJSON
+	if err := c.doJSON("GET", "/users", nil, &resp); err != nil {
+		return nil, err
+	}
+	out := make([]UserInfo, 0, len(resp))
+	for _, u := range resp {
+		out = append(out, UserInfo{
+			SignPub:   u.SignPub,
+			Handle:    u.Handle,
+			Role:      u.Role,
+			Status:    u.Status,
+			CreatedAt: u.CreatedAt,
+			RevokedAt: u.RevokedAt,
+		})
+	}
+	return out, nil
+}
+
+// AddUser registers a bus user from their Ed25519 signing public key (64-hex).
+// role is "admin" or "member" (empty defaults to member, matching the server).
+// The caller must be signing as an admin. Re-adding an already-registered key
+// returns an error (the server replies 409 and leaves the existing row
+// untouched — no silent role/status change).
+func (c *Client) AddUser(signPub, handle, role string) error {
+	return c.doJSON("POST", "/users", addUserReq{SignPub: signPub, Handle: handle, Role: role}, nil)
+}
+
+// RevokeUser revokes a bus user by their signing public key (64-hex). Revocation
+// is a status flip (no hard delete): the identity stays auditable and is denied
+// on both planes immediately. The caller must be signing as an admin.
+func (c *Client) RevokeUser(signPub string) error {
+	return c.doJSON("POST", "/users/"+signPub+"/revoke", nil, nil)
+}
+
 // newRoomKey returns 32 random bytes for a symmetric room key.
 func newRoomKey() ([]byte, error) {
 	k := make([]byte, 32)

pkg/client/users_test.go

@@ -0,0 +1,99 @@
+package client_test
+
+import (
+	"encoding/hex"
+	"strings"
+	"testing"
+
+	"github.com/enmanuel/unibus/pkg/client"
+	"github.com/enmanuel/unibus/pkg/membership"
+)
+
+// findUserInfo returns the row with the given signing key (case-insensitive).
+func findUserInfo(users []client.UserInfo, signPub string) (client.UserInfo, bool) {
+	want := strings.ToLower(signPub)
+	for _, u := range users {
+		if strings.ToLower(u.SignPub) == want {
+			return u, true
+		}
+	}
+	return client.UserInfo{}, false
+}
+
+// TestClientUsersAdminAPI drives the admin user-management API through the real
+// pkg/client methods against an in-process membershipd under enforce: an admin
+// client adds a user, lists it, revokes it, and sees the status flip — and a
+// non-admin client is denied. This is the path the admin panel uses, so it locks
+// the client/server contract the panel depends on.
+func TestClientUsersAdminAPI(t *testing.T) {
+	h := newHarnessMode(t, membership.AuthEnforce)
+	waitHealth(t, h.ctrlURL)
+
+	admin, err := client.New(h.natsURL, h.ctrlURL, mustIdentity(t))
+	if err != nil {
+		t.Fatalf("connect admin: %v", err)
+	}
+	defer admin.Close()
+	registerClient(t, h, admin, "admin", membership.RoleAdmin)
+
+	member, err := client.New(h.natsURL, h.ctrlURL, mustIdentity(t))
+	if err != nil {
+		t.Fatalf("connect member: %v", err)
+	}
+	defer member.Close()
+	registerClient(t, h, member, "member", membership.RoleMember)
+
+	// A brand-new identity the admin will register over HTTP.
+	carol := mustIdentity(t)
+	carolPub := hex.EncodeToString(carol.SignPub)
+
+	// Admin adds carol as a member.
+	if err := admin.AddUser(carolPub, "carol", membership.RoleMember); err != nil {
+		t.Fatalf("admin AddUser: %v", err)
+	}
+
+	// Admin lists: carol present and active.
+	users, err := admin.ListUsers()
+	if err != nil {
+		t.Fatalf("admin ListUsers: %v", err)
+	}
+	row, ok := findUserInfo(users, carolPub)
+	if !ok {
+		t.Fatalf("carol missing from list after add: %+v", users)
+	}
+	if row.Status != membership.StatusActive || row.Role != membership.RoleMember {
+		t.Fatalf("carol row wrong after add: %+v", row)
+	}
+
+	// Re-adding the same key is a conflict surfaced as an error (no silent upsert).
+	if err := admin.AddUser(carolPub, "carol-again", membership.RoleAdmin); err == nil {
+		t.Fatalf("re-adding carol should error (409), got nil")
+	}
+
+	// Admin revokes carol; list shows the status flip (no hard delete).
+	if err := admin.RevokeUser(carolPub); err != nil {
+		t.Fatalf("admin RevokeUser: %v", err)
+	}
+	users, err = admin.ListUsers()
+	if err != nil {
+		t.Fatalf("admin ListUsers after revoke: %v", err)
+	}
+	row, ok = findUserInfo(users, carolPub)
+	if !ok {
+		t.Fatalf("carol vanished after revoke (should be a status flip): %+v", users)
+	}
+	if row.Status != membership.StatusRevoked {
+		t.Fatalf("carol should be revoked, got status %q", row.Status)
+	}
+
+	// A non-admin (member) is denied on every user-management method.
+	if _, err := member.ListUsers(); err == nil {
+		t.Fatalf("non-admin ListUsers should error (403), got nil")
+	}
+	if err := member.AddUser(carolPub, "x", membership.RoleMember); err == nil {
+		t.Fatalf("non-admin AddUser should error (403), got nil")
+	}
+	if err := member.RevokeUser(carolPub); err == nil {
+		t.Fatalf("non-admin RevokeUser should error (403), got nil")
+	}
+}

pkg/membership/server.go

@@ -213,9 +213,12 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		writeErr(w, http.StatusUnauthorized, "unauthorized: "+err.Error())
 		return
 	}
-	// Carry the authenticated signer's endpoint into the handler so room handlers
-	// can authorize by membership (audit H3). Only set on a verified identity.
-	s.mux.ServeHTTP(w, r.WithContext(withSigner(r.Context(), res.endpoint)))
+	// Carry the authenticated signer's endpoint AND signing key into the handler.
+	// Room handlers authorize by membership via the endpoint (audit H3); the
+	// user-management handlers authorize by role via the signing key (the endpoint
+	// id is a one-way hash of the key, so it cannot be reversed to look the signer
+	// up in the user allowlist). Both are set only on a verified identity.
+	s.mux.ServeHTTP(w, r.WithContext(withSigner(r.Context(), res.endpoint, res.pubHex)))
 }
 
 // isBodyTooLarge reports whether err is the sentinel returned by MaxBytesReader
@@ -229,11 +232,19 @@ func isBodyTooLarge(err error) bool {
 // values cannot collide with keys set by other packages.
 type ctxKey int
 
-const ctxSignerEndpoint ctxKey = iota
+const (
+	ctxSignerEndpoint ctxKey = iota
+	ctxSignerPub
+)
 
-// withSigner returns a context carrying the authenticated signer's endpoint id.
-func withSigner(ctx context.Context, endpoint string) context.Context {
-	return context.WithValue(ctx, ctxSignerEndpoint, endpoint)
+// withSigner returns a context carrying the authenticated signer's endpoint id
+// and signing public key (lowercase hex). The endpoint authorizes room
+// membership; the signing key authorizes user-management by role, because the
+// endpoint id is a one-way hash of the key (base64url(sha256(signPub))) and so
+// cannot be reversed to look the signer up in the user allowlist.
+func withSigner(ctx context.Context, endpoint, pubHex string) context.Context {
+	ctx = context.WithValue(ctx, ctxSignerEndpoint, endpoint)
+	return context.WithValue(ctx, ctxSignerPub, pubHex)
 }
 
 // signerEndpoint returns the authenticated signer's endpoint id and whether one
@@ -245,6 +256,16 @@ func signerEndpoint(r *http.Request) (string, bool) {
 	return v, ok && v != ""
 }
 
+// signerPubHex returns the authenticated signer's signing public key (lowercase
+// hex) and whether one is present. Like signerEndpoint it is absent under
+// AuthOff and on a soft-mode pass-through; the user-management handlers treat
+// that absence as "no admin identity" and deny (default-deny), since a
+// privilege-granting operation must never run without a verified admin.
+func signerPubHex(r *http.Request) (string, bool) {
+	v, ok := r.Context().Value(ctxSignerPub).(string)
+	return v, ok && v != ""
+}
+
 // requireMember authorizes a room request by membership (audit H3): it returns
 // the signer endpoint and true when the request may proceed, or writes 403 and
 // returns false when an authenticated signer is not a member of roomID. When no
@@ -262,6 +283,31 @@ func (s *Server) requireMember(w http.ResponseWriter, r *http.Request, roomID st
 	return signer, true
 }
 
+// requireAdmin authorizes a user-management request: it returns the signer's
+// signing-key hex and true ONLY when the authenticated signer is a user with
+// role admin and active status; otherwise it writes 403 and returns false.
+//
+// Default-deny, with no dev relaxation: unlike requireMember (which allows a
+// request when no authenticated signer is present, preserving AuthOff/dev
+// behavior for room reads), this denies whenever the signer is absent or is not
+// a verified active admin. The user-management endpoints grant and revoke bus
+// access, so they must never be reachable without a verified admin identity —
+// the store is consulted on every call so a just-revoked admin is denied
+// immediately, and any store error fails closed.
+func (s *Server) requireAdmin(w http.ResponseWriter, r *http.Request) (string, bool) {
+	pubHex, ok := signerPubHex(r)
+	if !ok {
+		writeErr(w, http.StatusForbidden, "forbidden: admin role required")
+		return "", false
+	}
+	u, err := s.store.GetUser(pubHex)
+	if err != nil || u.Role != RoleAdmin || u.Status != StatusActive {
+		writeErr(w, http.StatusForbidden, "forbidden: admin role required")
+		return "", false
+	}
+	return pubHex, true
+}
+
 // isAuthExempt lists requests that bypass control-plane auth even under enforce.
 // Only the unauthenticated health probe qualifies: it carries no data and is
 // needed by load balancers / smoke checks / systemd before any identity exists.
@@ -280,6 +326,13 @@ func (s *Server) routes() {
 	s.mux.HandleFunc("GET /rooms/{id}", s.handleGetRoom)
 	s.mux.HandleFunc("POST /blobs", s.handlePutBlob)
 	s.mux.HandleFunc("GET /blobs/{hash}", s.handleGetBlob)
+	// User-management (admin-only) — the HTTP-signed equivalent of the local
+	// `membershipd user` CLI, so the admin panel manages the bus allowlist by
+	// signing as an admin instead of needing direct store/KV access. All three
+	// pass through requireAdmin; they hit the same store the room handlers do.
+	s.mux.HandleFunc("GET /users", s.handleListUsers)
+	s.mux.HandleFunc("POST /users", s.handleAddUser)
+	s.mux.HandleFunc("POST /users/{signpub}/revoke", s.handleRevokeUser)
 }
 
 // ---- wire types -----------------------------------------------------------
@@ -357,6 +410,27 @@ type blobResp struct {
 	Hash string `json:"hash"`
 }
 
+// userJSON is the wire representation of a bus user on the admin endpoints. It
+// carries the full record the panel needs to render the allowlist, including
+// status (so revoked users are visible) and the timestamps. revoked_at is
+// omitted for an active user.
+type userJSON struct {
+	SignPub   string `json:"sign_pub"`
+	Handle    string `json:"handle"`
+	Role      string `json:"role"`
+	Status    string `json:"status"`
+	CreatedAt string `json:"created_at"`
+	RevokedAt string `json:"revoked_at,omitempty"`
+}
+
+// addUserReq is the POST /users body: the new user's Ed25519 signing key
+// (64-hex), human handle, and role. role is optional and defaults to member.
+type addUserReq struct {
+	SignPub string `json:"sign_pub"`
+	Handle  string `json:"handle"`
+	Role    string `json:"role"`
+}
+
 // ---- helpers --------------------------------------------------------------
 
 func writeJSON(w http.ResponseWriter, code int, v any) {
@@ -674,3 +748,95 @@ func (s *Server) handleGetBlob(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusOK)
 	_, _ = w.Write(data)
 }
+
+// ---- user-management handlers (admin-only) --------------------------------
+
+// handleListUsers returns the full bus allowlist, including revoked users, so an
+// admin sees the complete picture (a revoked identity stays auditable). Admin-only.
+func (s *Server) handleListUsers(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireAdmin(w, r); !ok {
+		return
+	}
+	users, err := s.store.ListUsers()
+	if err != nil {
+		writeServerErr(w, r, http.StatusInternalServerError, "internal error", err)
+		return
+	}
+	out := make([]userJSON, 0, len(users))
+	for _, u := range users {
+		out = append(out, userJSON{
+			SignPub:   u.SignPub,
+			Handle:    u.Handle,
+			Role:      u.Role,
+			Status:    u.Status,
+			CreatedAt: u.CreatedAt,
+			RevokedAt: u.RevokedAt,
+		})
+	}
+	writeJSON(w, http.StatusOK, out)
+}
+
+// handleAddUser registers a new bus user from an admin-supplied Ed25519 signing
+// key. It mirrors the `membershipd user add` CLI: the key must be 64-hex, the
+// role must be admin or member (empty defaults to member), and re-adding an
+// already-registered key is a 409 that leaves the existing row untouched — no
+// silent upsert that could flip a role or clobber status. Admin-only.
+func (s *Server) handleAddUser(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireAdmin(w, r); !ok {
+		return
+	}
+	var req addUserReq
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeErr(w, http.StatusBadRequest, "bad json: "+err.Error())
+		return
+	}
+	if req.SignPub == "" || req.Handle == "" {
+		writeErr(w, http.StatusBadRequest, "sign_pub and handle required")
+		return
+	}
+	if err := ValidateSignPubHex(req.SignPub); err != nil {
+		writeErr(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	role := req.Role
+	if role == "" {
+		role = RoleMember
+	}
+	if role != RoleAdmin && role != RoleMember {
+		writeErr(w, http.StatusBadRequest,
+			fmt.Sprintf("invalid role %q (want %q or %q)", role, RoleAdmin, RoleMember))
+		return
+	}
+	if err := s.store.AddUser(req.SignPub, req.Handle, role); err != nil {
+		if errors.Is(err, ErrUserExists) {
+			// Idempotency contract (mirrors the CLI): re-adding a key is an explicit,
+			// non-destructive conflict. To replace a user, revoke then add again.
+			writeErr(w, http.StatusConflict,
+				"user already registered (unchanged); revoke it first to replace")
+			return
+		}
+		writeServerErr(w, r, http.StatusInternalServerError, "internal error", err)
+		return
+	}
+	writeJSON(w, http.StatusCreated, map[string]string{"status": "added"})
+}
+
+// handleRevokeUser revokes a bus user by signing key. Revocation is a status
+// flip (no hard delete) so the identity stays auditable and IsAuthorized denies
+// it on both planes immediately. Revoking an unknown or already-revoked key is a
+// 404. Admin-only.
+func (s *Server) handleRevokeUser(w http.ResponseWriter, r *http.Request) {
+	if _, ok := s.requireAdmin(w, r); !ok {
+		return
+	}
+	signPub := r.PathValue("signpub")
+	if err := ValidateSignPubHex(signPub); err != nil {
+		writeErr(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	if err := s.store.RevokeUser(signPub); err != nil {
+		writeServerErr(w, r, http.StatusNotFound, "no active user with that key", err)
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]string{"status": "revoked"})
+}

pkg/membership/users.go

@@ -2,6 +2,7 @@ package membership
 
 import (
 	"database/sql"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"strings"
@@ -35,6 +36,23 @@ type User struct {
 	RevokedAt string // empty unless revoked
 }
 
+// ValidateSignPubHex ensures signPub is exactly a 32-byte Ed25519 public key in
+// hex (64 hex chars). It is the single source of truth for that check, shared by
+// the local admin CLI (which validates before seeding the first admin) and the
+// HTTP user-management handlers (which validate an admin-supplied key before it
+// reaches the store). Catching a malformed key here turns a silent "authorized
+// nobody" into an explicit error at the boundary.
+func ValidateSignPubHex(signPub string) error {
+	b, err := hex.DecodeString(signPub)
+	if err != nil {
+		return fmt.Errorf("sign-pub is not valid hex: %w", err)
+	}
+	if len(b) != 32 {
+		return fmt.Errorf("sign-pub must be a 32-byte Ed25519 public key (64 hex chars), got %d bytes", len(b))
+	}
+	return nil
+}
+
 // normalizeSignPub lowercases the hex key so lookups are case-insensitive: the
 // primary key is stored lowercase and every query normalizes its input the same
 // way, so a caller passing uppercase hex still matches.

pkg/membership/users_http_test.go

@@ -0,0 +1,164 @@
+package membership
+
+import (
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"testing"
+	"time"
+
+	cs "fn-registry/functions/cybersecurity"
+)
+
+// signedJSON is signedReq for a JSON body: it marshals v and signs the request
+// as id with a distinct nonce. It returns the response status and body, reusing
+// the auth_test harness so these tests exercise the real signed wire contract.
+func signedJSON(t *testing.T, h *authHarness, method, path string, v any, id cs.Identity, n int) (int, string) {
+	t.Helper()
+	var body []byte
+	if v != nil {
+		b, err := json.Marshal(v)
+		if err != nil {
+			t.Fatalf("marshal body: %v", err)
+		}
+		body = b
+	}
+	return do(t, signedReq(t, h.ts.URL, method, path, body, id, time.Now().Unix(), nonceN(n)))
+}
+
+// TestUsersHTTP_NonAdminForbidden is the security spine: a REGISTERED but
+// non-admin signer (bob, role member) is denied on every user-management
+// endpoint. His signature clears auth (he is in the allowlist), so each request
+// reaches the handler, where requireAdmin returns 403 — default-deny by role.
+func TestUsersHTTP_NonAdminForbidden(t *testing.T) {
+	h := newAuthHarness(t, AuthEnforce)
+
+	bob, _ := cs.GenerateIdentity()
+	register(t, h, bob, "bob") // role member (see register in authz_test.go)
+	bobPub := hex.EncodeToString(bob.SignPub)
+
+	victim, _ := cs.GenerateIdentity()
+	victimPub := hex.EncodeToString(victim.SignPub)
+
+	checks := []struct {
+		name   string
+		method string
+		path   string
+		body   any
+	}{
+		{"list users", "GET", "/users", nil},
+		{"add user", "POST", "/users", addUserReq{SignPub: victimPub, Handle: "mallory", Role: RoleMember}},
+		{"revoke user", "POST", "/users/" + bobPub + "/revoke", nil},
+	}
+	for i, c := range checks {
+		code, body := signedJSON(t, h, c.method, c.path, c.body, bob, i+1)
+		if code != http.StatusForbidden {
+			t.Fatalf("non-admin %s should be 403, got %d (%s)", c.name, code, body)
+		}
+	}
+}
+
+// TestUsersHTTP_AdminRoundtrip exercises the golden path end to end: alice (the
+// seeded admin) adds carol, sees her in the list as active, revokes her, then
+// sees her status flip to revoked (no hard delete — she stays in the list).
+func TestUsersHTTP_AdminRoundtrip(t *testing.T) {
+	h := newAuthHarness(t, AuthEnforce)
+
+	carol, _ := cs.GenerateIdentity()
+	carolPub := hex.EncodeToString(carol.SignPub)
+
+	// Add carol as a member.
+	if code, body := signedJSON(t, h, "POST", "/users",
+		addUserReq{SignPub: carolPub, Handle: "carol", Role: RoleMember}, h.alice, 1); code != http.StatusCreated {
+		t.Fatalf("admin add carol should be 201, got %d (%s)", code, body)
+	}
+
+	// List: carol present and active; alice (the seed admin) also present.
+	users := listUsers(t, h, 2)
+	carolRow, ok := findUser(users, carolPub)
+	if !ok {
+		t.Fatalf("carol missing from list after add: %+v", users)
+	}
+	if carolRow.Status != StatusActive || carolRow.Role != RoleMember || carolRow.Handle != "carol" {
+		t.Fatalf("carol row wrong after add: %+v", carolRow)
+	}
+	if _, ok := findUser(users, h.alicePub); !ok {
+		t.Fatalf("seeded admin alice missing from list: %+v", users)
+	}
+
+	// Revoke carol.
+	if code, body := signedJSON(t, h, "POST", "/users/"+carolPub+"/revoke", nil, h.alice, 3); code != http.StatusOK {
+		t.Fatalf("admin revoke carol should be 200, got %d (%s)", code, body)
+	}
+
+	// List again: carol still present, now revoked (status flip, not delete).
+	users = listUsers(t, h, 4)
+	carolRow, ok = findUser(users, carolPub)
+	if !ok {
+		t.Fatalf("carol vanished from list after revoke (should be a status flip): %+v", users)
+	}
+	if carolRow.Status != StatusRevoked {
+		t.Fatalf("carol should be revoked, got status %q", carolRow.Status)
+	}
+}
+
+// TestUsersHTTP_Validation covers the input-validation contract: a malformed hex
+// key is 400, an unknown role is 400, and re-adding an already-registered key is
+// 409 (the existing row is left untouched — no silent upsert).
+func TestUsersHTTP_Validation(t *testing.T) {
+	h := newAuthHarness(t, AuthEnforce)
+
+	good, _ := cs.GenerateIdentity()
+	goodPub := hex.EncodeToString(good.SignPub)
+
+	// Invalid hex (too short) -> 400.
+	if code, body := signedJSON(t, h, "POST", "/users",
+		addUserReq{SignPub: "abcd", Handle: "shorty", Role: RoleMember}, h.alice, 1); code != http.StatusBadRequest {
+		t.Fatalf("malformed sign_pub should be 400, got %d (%s)", code, body)
+	}
+
+	// Invalid role -> 400.
+	if code, body := signedJSON(t, h, "POST", "/users",
+		addUserReq{SignPub: goodPub, Handle: "weirdrole", Role: "superuser"}, h.alice, 2); code != http.StatusBadRequest {
+		t.Fatalf("invalid role should be 400, got %d (%s)", code, body)
+	}
+
+	// Re-adding the seeded admin's own key -> 409 (idempotency, no overwrite).
+	if code, body := signedJSON(t, h, "POST", "/users",
+		addUserReq{SignPub: h.alicePub, Handle: "alice-again", Role: RoleMember}, h.alice, 3); code != http.StatusConflict {
+		t.Fatalf("re-adding an existing key should be 409, got %d (%s)", code, body)
+	}
+	// And the existing row is untouched: alice is still an active admin.
+	u, err := h.store.GetUser(h.alicePub)
+	if err != nil {
+		t.Fatalf("get alice after conflicting re-add: %v", err)
+	}
+	if u.Role != RoleAdmin || u.Status != StatusActive || u.Handle != "alice" {
+		t.Fatalf("conflicting re-add mutated the existing row: %+v", u)
+	}
+}
+
+// listUsers signs a GET /users as alice and decodes the response.
+func listUsers(t *testing.T, h *authHarness, n int) []userJSON {
+	t.Helper()
+	code, body := signedJSON(t, h, "GET", "/users", nil, h.alice, n)
+	if code != http.StatusOK {
+		t.Fatalf("admin list users should be 200, got %d (%s)", code, body)
+	}
+	var users []userJSON
+	if err := json.Unmarshal([]byte(body), &users); err != nil {
+		t.Fatalf("decode users: %v (%s)", err, body)
+	}
+	return users
+}
+
+// findUser returns the row with the given signing key (case-insensitive).
+func findUser(users []userJSON, signPub string) (userJSON, bool) {
+	want := normalizeSignPub(signPub)
+	for _, u := range users {
+		if normalizeSignPub(u.SignPub) == want {
+			return u, true
+		}
+	}
+	return userJSON{}, false
+}