Built-in Groups admin screen (todo §5); /admin/groups list (search/sort/paginate) + create/delete + membership (add/remove users & nested groups), writing only to Keto — gated admin-only + CSRF-guarded like Users (Kratos read only to label pickers). A group = Keto subject set Group:<name>#members, exists while it has ≥1 member: create writes the first-member tuple, delete removes all by partial-filter. Extracted shared admin-nav.ts (Dashboard·Users·Groups); new generic rowHeader <th scope=row> data-table cell. Stability-reviewer run as a local PR: symmetric subject UUID-validation, duplicate-name rejection, malformed-%→404. 228→237 units + typecheck green; core Keto interactions boot-verified live

src/admin-groups.test.ts

@@ -0,0 +1,112 @@
+// Built-in Groups admin screen (§5): the pure view-model + Keto-tuple builders. A group is a
+// Keto subject set (Group:<name>#members); membership tuples carry users (subject_id) or nested
+// groups (subject_set). The HTTP routing/gate/CSRF + live Keto/Kratos calls are exercised over
+// HTTP in app.test.ts.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import {
+  buildGroupDetailModel,
+  buildGroupFormModel,
+  buildGroupsListModel,
+  groupsFromTuples,
+  isValidGroupName,
+  memberTuple,
+  memberView,
+  parseSubject,
+} from "./admin-groups.ts";
+import type { RelationTuple } from "./keto-client.ts";
+
+const uid = (n: number) => `01902d5e-7b6c-7e3a-9f21-3c8d1e0a4b${String(n).padStart(2, "0")}`;
+const userTuple = (group: string, n: number): RelationTuple =>
+  ({ namespace: "Group", object: group, relation: "members", subject_id: `user:${uid(n)}` });
+const groupTuple = (group: string, child: string): RelationTuple =>
+  ({ namespace: "Group", object: group, relation: "members", subject_set: { namespace: "Group", object: child, relation: "members" } });
+
+test("isValidGroupName accepts URL-safe names, rejects empties/spaces/uppercase/leading punctuation", () => {
+  for (const ok of ["eng", "team-a", "a1_b9", "x"]) assert.equal(isValidGroupName(ok), true, ok);
+  for (const bad of ["", "Eng", "a b", "-bad", "_bad", "a/b", "a".repeat(65)]) assert.equal(isValidGroupName(bad), false, bad);
+});
+
+test("parseSubject + memberTuple map the form value to the user/nested-group subject (else null)", () => {
+  assert.deepEqual(parseSubject(`user:${uid(1)}`), { subject_id: `user:${uid(1)}` });
+  assert.deepEqual(parseSubject("group:eng"), { subject_set: { namespace: "Group", object: "eng", relation: "members" } });
+  // Both forms are validated: a non-UUID user / invalid group name is rejected, not written blindly.
+  for (const bad of ["", "user:", "user:not-a-uuid", "group:", "group:Bad Name", "nope:x", "plain"]) assert.equal(parseSubject(bad), null, bad);
+
+  assert.deepEqual(memberTuple("design", `user:${uid(2)}`), { namespace: "Group", object: "design", relation: "members", subject_id: `user:${uid(2)}` });
+  assert.deepEqual(memberTuple("design", "group:eng"), { namespace: "Group", object: "design", relation: "members", subject_set: { namespace: "Group", object: "eng", relation: "members" } });
+  assert.equal(memberTuple("design", "bad"), null);
+});
+
+test("groupsFromTuples collapses membership tuples → distinct groups + member counts, sorted by name", () => {
+  const tuples = [userTuple("eng", 1), userTuple("eng", 2), groupTuple("eng", "design"), userTuple("design", 3)];
+  assert.deepEqual(groupsFromTuples(tuples), [
+    { memberCount: 1, name: "design" },
+    { memberCount: 3, name: "eng" },
+  ]);
+});
+
+test("memberView resolves a user subject to its email (else the raw id) and a subject_set to the group", () => {
+  const emails = new Map([[uid(1), "ada@example.com"]]);
+  assert.deepEqual(memberView(userTuple("eng", 1), emails), { kind: "user", label: "ada@example.com", subject: `user:${uid(1)}` });
+  assert.deepEqual(memberView(userTuple("eng", 9), emails), { kind: "user", label: `user:${uid(9)}`, subject: `user:${uid(9)}` });
+  assert.deepEqual(memberView(groupTuple("eng", "design"), emails), { kind: "group", label: "design", subject: "group:design" });
+});
+
+test("buildGroupsListModel filters by search, sorts, paginates; the name links to the detail page", () => {
+  const groups = Array.from({ length: 30 }, (_, i) => ({ memberCount: i + 1, name: `team-${String(i).padStart(2, "0")}` }));
+
+  const all = buildGroupsListModel({ groups, url: "http://x/admin/groups" });
+  assert.equal(all.pagination.summary.total, 30);
+  assert.equal(all.table.rows.length, 25); // default page size
+  assert.equal(all.shell.title, "Groups");
+  // The group name is the row header, linking to its detail page.
+  const first = all.table.rows[0]!.cells[0] as { rowHeader: { href: string; text: string } };
+  assert.equal(first.rowHeader.text, "team-00");
+  assert.equal(first.rowHeader.href, "/admin/groups/team-00");
+
+  // Search narrows + shows a pill.
+  const one = buildGroupsListModel({ groups, url: "http://x/admin/groups?q=team-07" });
+  assert.equal(one.pagination.summary.total, 1);
+  assert.deepEqual(one.filterBar.pills.map((p) => p.label), ["Search"]);
+
+  // Sort by members descending puts the biggest group first.
+  const desc = buildGroupsListModel({ groups, url: "http://x/admin/groups?sort=-members" });
+  assert.equal((desc.table.rows[0]!.cells[0] as { rowHeader: { text: string } }).rowHeader.text, "team-29");
+});
+
+test("buildGroupFormModel: a create form with a required name field + member options, no group of its own", () => {
+  const options = [{ label: "ada@example.com", value: `user:${uid(1)}` }, { label: "eng (group)", value: "group:eng" }];
+  const m = buildGroupFormModel({ csrfToken: "tok.sig", memberOptions: options });
+  assert.equal(m.shell.title, "New group");
+  assert.equal(m.form.action, "/admin/groups");
+  assert.equal(m.form.submitLabel, "Create group");
+  assert.equal(m.form.csrfToken, "tok.sig");
+  assert.equal(m.form.nameField.name, "name");
+  assert.equal(m.form.nameField.required, true);
+  assert.deepEqual(m.form.memberOptions, options);
+
+  // An error (e.g. a taken/invalid name) re-renders with the submitted values.
+  const err = buildGroupFormModel({ error: "That name is taken.", memberOptions: options, values: { member: "group:eng", name: "Eng" } });
+  assert.equal(err.error, "That name is taken.");
+  assert.equal(err.form.nameField.value, "Eng");
+  assert.equal(err.form.selectedMember, "group:eng");
+});
+
+test("buildGroupDetailModel: members → rows, add-options exclude current members + the group itself, delete/remove wired", () => {
+  const members = [memberView(userTuple("eng", 1), new Map([[uid(1), "ada@example.com"]])), memberView(groupTuple("eng", "design"), new Map())];
+  const candidates = [
+    { label: "ada@example.com", value: `user:${uid(1)}` }, // already a member → excluded
+    { label: "grace@example.com", value: `user:${uid(2)}` },
+    { label: "design (group)", value: "group:design" }, // already a member → excluded
+    { label: "eng (group)", value: "group:eng" }, // the group itself → excluded
+    { label: "ops (group)", value: "group:ops" },
+  ];
+  const m = buildGroupDetailModel({ candidates, group: { name: "eng" }, members });
+  assert.equal(m.shell.title, "eng");
+  assert.equal(m.members.rows.length, 2);
+  assert.equal(m.members.action, "/admin/groups/eng/members/delete");
+  assert.equal(m.add.action, "/admin/groups/eng/members");
+  assert.deepEqual(m.add.options.map((o) => o.value), [`user:${uid(2)}`, "group:ops"]);
+  assert.equal(m.delete.action, "/admin/groups/eng/delete");
+});

src/admin-groups.ts

@@ -0,0 +1,410 @@
+// Built-in Groups admin screen (todo §5): list / create / delete Keto groups and manage their
+// membership. A group is a Keto subject set `Group:<name>#members`; a membership tuple's subject is
+// a user (`subject_id = user:<id>`) or a nested group (`subject_set = Group:<other>#members`). Writes
+// go only to Keto (README "stateless"); there is no group store. Keto has no "create object" — a
+// group exists exactly while it has ≥1 member, so creating one writes its first-member tuple and
+// deleting one removes every member tuple. The pure builders turn tuples + the request URL into the
+// building-block view models; `handleAdminGroups` is the imperative shell app.ts dispatches to — it
+// gates (admin only), CSRF-guards every mutation, and maps each action to a RouteResult.
+
+import { ADMIN_GROUPS_BASE, ADMIN_PERMISSION, adminNav } from "./admin-nav.ts";
+import type { FieldConfig } from "./admin-users.ts";
+import { readFormBody } from "./body.ts";
+import type { RequestContext, User } from "./context.ts";
+import { CSRF_FIELD, verifyCsrfRequest } from "./csrf.ts";
+import { GuardError } from "./guards.ts";
+import type { KetoClient, RelationQuery, RelationTuple, SubjectSet } from "./keto-client.ts";
+import type { KratosAdmin } from "./kratos-admin.ts";
+import { parseListQuery } from "./list-query.ts";
+import { DEFAULT_MENU, type MenuConfig } from "./menu-config.ts";
+import { paginate } from "./paginate.ts";
+import type { RouteResult } from "./plugin.ts";
+import { buildShellContext } from "./shell-context.ts";
+
+const GROUP_NS = "Group";
+const MEMBERS = "members";
+const DEFAULT_PAGE_SIZE = 25;
+const PAGE_SIZES = [25, 50, 100];
+// One Keto page of candidate users is fetched for the member pickers (mirrors admin-users).
+const LIST_FETCH_SIZE = 250;
+const GROUP_NAME = /^[a-z0-9][a-z0-9_-]*$/; // URL-safe; doubles as the path segment
+const UUID = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i; // a Kratos identity id
+
+export interface GroupView {
+  memberCount: number;
+  name: string;
+}
+
+// A member's view model: a user (label = email) or a nested group (label = group name). `subject`
+// is the form value that round-trips it — `user:<id>` or `group:<name>` (see parseSubject).
+export interface MemberView {
+  kind: "group" | "user";
+  label: string;
+  subject: string;
+}
+
+// One option in a member <select>.
+export interface MemberOption {
+  label: string;
+  value: string; // `user:<id>` | `group:<name>`
+}
+
+export function isValidGroupName(name: string): boolean {
+  return name.length <= 64 && GROUP_NAME.test(name);
+}
+
+// Map a member-picker value → the Keto subject (subject_id for a user, subject_set for a nested
+// group). Returns null for anything unrecognised (a crafted/empty POST).
+export function parseSubject(value: string): { subject_id: string } | { subject_set: SubjectSet } | null {
+  const sep = value.indexOf(":");
+  if (sep <= 0) return null;
+  const rest = value.slice(sep + 1);
+  if (!rest) return null;
+  // Validate both subject forms so a crafted POST can't write a dangling tuple (the pickers only
+  // ever offer real users/groups): a user id is a Kratos UUID, a nested group a valid group name.
+  if (value.slice(0, sep) === "user") return UUID.test(rest) ? { subject_id: `user:${rest}` } : null;
+  if (value.slice(0, sep) === "group") return isValidGroupName(rest) ? { subject_set: { namespace: GROUP_NS, object: rest, relation: MEMBERS } } : null;
+  return null;
+}
+
+// The full membership tuple for adding/removing `value` to/from `group` (null if value is invalid).
+export function memberTuple(group: string, value: string): RelationTuple | null {
+  const subject = parseSubject(value);
+  return subject ? { namespace: GROUP_NS, object: group, relation: MEMBERS, ...subject } : null;
+}
+
+// Collapse the namespace's membership tuples → distinct groups + member counts, sorted by name.
+export function groupsFromTuples(tuples: RelationTuple[]): GroupView[] {
+  const counts = new Map<string, number>();
+  for (const t of tuples) counts.set(t.object, (counts.get(t.object) ?? 0) + 1);
+  return [...counts].map(([name, memberCount]) => ({ memberCount, name })).sort((a, b) => a.name.localeCompare(b.name));
+}
+
+export function memberView(tuple: RelationTuple, emailById: Map<string, string>): MemberView {
+  if (tuple.subject_set) return { kind: "group", label: tuple.subject_set.object, subject: `group:${tuple.subject_set.object}` };
+  const subjectId = tuple.subject_id ?? "";
+  const id = subjectId.startsWith("user:") ? subjectId.slice("user:".length) : subjectId;
+  return { kind: "user", label: emailById.get(id) ?? subjectId, subject: subjectId };
+}
+
+// ---- list view model ----
+
+interface ListState {
+  page: number;
+  pageSize: number;
+  q: string;
+  sort: string | null;
+}
+
+const SORT: Record<string, (g: GroupView) => number | string> = {
+  members: (g) => g.memberCount,
+  name: (g) => g.name,
+};
+const COLUMNS = [
+  { key: "name", label: "Group" },
+  { key: "members", label: "Members" },
+];
+
+function detailHref(name: string): string {
+  return `${ADMIN_GROUPS_BASE}/${encodeURIComponent(name)}`;
+}
+
+function listHref(state: ListState, overrides: Partial<ListState> = {}): string {
+  const s = { ...state, ...overrides };
+  const p = new URLSearchParams();
+  if (s.q) p.set("q", s.q);
+  if (s.sort) p.set("sort", s.sort);
+  if (s.page > 1) p.set("page", String(s.page));
+  if (s.pageSize !== DEFAULT_PAGE_SIZE) p.set("pageSize", String(s.pageSize));
+  const qs = p.toString();
+  return qs ? `${ADMIN_GROUPS_BASE}?${qs}` : ADMIN_GROUPS_BASE;
+}
+
+export function buildGroupsListModel(opts: {
+  csrfToken?: string;
+  groups: GroupView[];
+  menu?: MenuConfig;
+  url: URL | URLSearchParams | string;
+  user?: User | null;
+}) {
+  const menu = opts.menu ?? DEFAULT_MENU;
+  const query = parseListQuery(opts.url, { defaultPageSize: DEFAULT_PAGE_SIZE });
+  const sort = query.sort && SORT[query.sort.field] ? query.sort : null;
+  const sortToken = sort ? (sort.dir === "desc" ? `-${sort.field}` : sort.field) : null;
+  const needle = query.q.toLowerCase();
+
+  let list = opts.groups.filter((g) => !needle || g.name.toLowerCase().includes(needle));
+  if (sort) {
+    const get = SORT[sort.field]!;
+    const dir = sort.dir === "desc" ? -1 : 1;
+    list = [...list].sort((a, b) => {
+      const av = get(a), bv = get(b);
+      const cmp = typeof av === "number" && typeof bv === "number" ? av - bv : String(av).localeCompare(String(bv));
+      return cmp * dir;
+    });
+  }
+
+  const page = paginate(list.length, query.page, query.pageSize, { boundaries: 1, siblings: 1 });
+  const start = (page.page - 1) * page.pageSize;
+  const rows = list.slice(start, start + page.pageSize);
+  const state: ListState = { page: page.page, pageSize: page.pageSize, q: query.q, sort: sortToken };
+
+  return {
+    filterBar: listFilterBar(state),
+    nav: adminNav(opts.user?.roles ?? [], menu, "groups"),
+    pagination: listPagination(state, page),
+    shell: buildShellContext({
+      breadcrumbs: [{ href: ADMIN_GROUPS_BASE, label: "Admin" }, { label: "Groups" }],
+      csrfToken: opts.csrfToken ?? "",
+      menu,
+      title: "Groups",
+      user: opts.user ?? null,
+    }),
+    table: listTable(rows, state, sort),
+  };
+}
+
+function listTable(rows: GroupView[], state: ListState, sort: { dir: "asc" | "desc"; field: string } | null) {
+  return {
+    caption: "Groups",
+    columns: COLUMNS.map((c) => {
+      const dir = sort && sort.field === c.key ? sort.dir : undefined;
+      const next = dir === "asc" ? `-${c.key}` : c.key;
+      return { href: listHref(state, { page: 1, sort: next }), label: c.label, sort: dir, sortable: true };
+    }),
+    rows: rows.map((g) => ({
+      cells: [{ rowHeader: { href: detailHref(g.name), text: g.name } }, String(g.memberCount)],
+      name: g.name,
+    })),
+  };
+}
+
+function listFilterBar(state: ListState) {
+  const pills: { label: string; remove: string; value: string }[] = [];
+  if (state.q) pills.push({ label: "Search", remove: listHref(state, { page: 1, q: "" }), value: state.q });
+  return {
+    applyLabel: "Apply",
+    clearHref: ADMIN_GROUPS_BASE,
+    label: "Filter groups",
+    pills,
+    rows: [[
+      { label: "Search groups", name: "q", placeholder: "Search group name…", type: "search", value: state.q },
+      { type: "spacer" },
+    ]],
+  };
+}
+
+function listPagination(state: ListState, page: ReturnType<typeof paginate>) {
+  const hidden: { name: string; value: string }[] = [];
+  if (state.q) hidden.push({ name: "q", value: state.q });
+  if (state.sort) hidden.push({ name: "sort", value: state.sort });
+  return {
+    label: "Groups pagination",
+    next: { href: page.next ? listHref(state, { page: page.next }) : undefined },
+    pages: page.pages.map((p) =>
+      p.ellipsis ? { ellipsis: true }
+        : p.current ? { current: true, label: String(p.page) }
+          : { href: listHref(state, { page: p.page as number }), label: String(p.page) }),
+    prev: { href: page.prev ? listHref(state, { page: page.prev }) : undefined },
+    rows: { hidden, label: "Rows", name: "pageSize", options: PAGE_SIZES, submitLabel: "Go", value: state.pageSize },
+    summary: { from: page.from, to: page.to, total: page.total },
+  };
+}
+
+// ---- create form + detail view models ----
+
+export function buildGroupFormModel(opts: {
+  csrfToken?: string;
+  error?: string;
+  memberOptions: MemberOption[];
+  menu?: MenuConfig;
+  user?: User | null;
+  values?: { member?: string; name?: string };
+}) {
+  const menu = opts.menu ?? DEFAULT_MENU;
+  const nameField: FieldConfig = {
+    autocomplete: "off", hint: "Lowercase letters, digits, dashes and underscores.", icon: "i-layers",
+    id: "name", label: "Group name", name: "name", required: true, value: opts.values?.name ?? "",
+  };
+  return {
+    error: opts.error,
+    form: {
+      action: ADMIN_GROUPS_BASE,
+      cancelHref: ADMIN_GROUPS_BASE,
+      csrfToken: opts.csrfToken ?? "",
+      memberOptions: opts.memberOptions,
+      nameField,
+      selectedMember: opts.values?.member ?? "",
+      submitLabel: "Create group",
+    },
+    nav: adminNav(opts.user?.roles ?? [], menu, "groups"),
+    shell: buildShellContext({
+      breadcrumbs: [{ href: ADMIN_GROUPS_BASE, label: "Groups" }, { label: "New" }],
+      csrfToken: opts.csrfToken ?? "",
+      menu,
+      title: "New group",
+      user: opts.user ?? null,
+    }),
+  };
+}
+
+export function buildGroupDetailModel(opts: {
+  candidates: MemberOption[];
+  csrfToken?: string;
+  error?: string;
+  group: { name: string };
+  members: MemberView[];
+  menu?: MenuConfig;
+  user?: User | null;
+}) {
+  const menu = opts.menu ?? DEFAULT_MENU;
+  const name = opts.group.name;
+  const base = detailHref(name);
+  const taken = new Set(opts.members.map((m) => m.subject));
+  const self = `group:${name}`; // a group can't be a member of itself
+  const options = opts.candidates.filter((c) => c.value !== self && !taken.has(c.value));
+  return {
+    add: { action: `${base}/members`, options },
+    csrfToken: opts.csrfToken ?? "",
+    delete: { action: `${base}/delete` },
+    error: opts.error,
+    group: { name },
+    members: { action: `${base}/members/delete`, rows: opts.members },
+    nav: adminNav(opts.user?.roles ?? [], menu, "groups"),
+    shell: buildShellContext({
+      breadcrumbs: [{ href: ADMIN_GROUPS_BASE, label: "Groups" }, { label: name }],
+      csrfToken: opts.csrfToken ?? "",
+      menu,
+      title: name,
+      user: opts.user ?? null,
+    }),
+  };
+}
+
+// ---- request handler (imperative shell) ----
+
+export interface AdminGroupsDeps {
+  csrfSecret: string;
+  keto: KetoClient;
+  kratosAdmin: KratosAdmin;
+  menu: MenuConfig;
+  render: (view: string, data: Record<string, unknown>) => Promise<string>;
+}
+
+// Drain every page of a relation-tuple query.
+async function pagedTuples(keto: KetoClient, query: RelationQuery): Promise<RelationTuple[]> {
+  const out: RelationTuple[] = [];
+  let pageToken: string | undefined;
+  do {
+    const page = await keto.listRelations({ ...query, ...(pageToken ? { pageToken } : {}) });
+    out.push(...page.tuples);
+    pageToken = page.nextPageToken ?? undefined;
+  } while (pageToken);
+  return out;
+}
+
+// Build the member-picker options (every user by email + every existing group) and the id→email map
+// detail rows render with. One Kratos page + one Keto scan; ample for an admin tool.
+async function memberCandidates(keto: KetoClient, kratosAdmin: KratosAdmin): Promise<{ emailById: Map<string, string>; options: MemberOption[] }> {
+  const { identities } = await kratosAdmin.listIdentities({ pageSize: LIST_FETCH_SIZE });
+  const emailById = new Map<string, string>();
+  const userOptions: MemberOption[] = [];
+  for (const it of identities) {
+    const trait = it.traits?.["email"];
+    const email = typeof trait === "string" ? trait : it.id;
+    emailById.set(it.id, email);
+    userOptions.push({ label: email, value: `user:${it.id}` });
+  }
+  const groups = groupsFromTuples(await pagedTuples(keto, { namespace: GROUP_NS, relation: MEMBERS }));
+  return { emailById, options: [...userOptions, ...groups.map((g) => ({ label: `${g.name} (group)`, value: `group:${g.name}` }))] };
+}
+
+// A group exists exactly while it has ≥1 member.
+async function groupExists(keto: KetoClient, name: string): Promise<boolean> {
+  const page = await keto.listRelations({ namespace: GROUP_NS, object: name, relation: MEMBERS, pageSize: 1 });
+  return page.tuples.length > 0;
+}
+
+// Decode a path segment without letting malformed %-encoding throw (→ caller treats it as not found).
+function safeDecode(seg: string): string | null {
+  try { return decodeURIComponent(seg); } catch { return null; }
+}
+
+export async function handleAdminGroups(ctx: RequestContext, csrfToken: string, deps: AdminGroupsDeps): Promise<RouteResult | null> {
+  const path = ctx.url.pathname;
+  if (path !== ADMIN_GROUPS_BASE && !path.startsWith(`${ADMIN_GROUPS_BASE}/`)) return null;
+
+  if (!ctx.user) throw new GuardError(401, "authentication required", "/login");
+  if (!ctx.roles.includes(ADMIN_PERMISSION)) throw new GuardError(403, "admin role required");
+
+  const { keto, kratosAdmin, menu, render } = deps;
+  const user = ctx.user;
+  const method = (ctx.req.method ?? "GET").toUpperCase();
+  const seg = path.slice(ADMIN_GROUPS_BASE.length).split("/").filter(Boolean);
+
+  let form: URLSearchParams | undefined;
+  if (method === "POST") {
+    form = await readFormBody(ctx.req);
+    if (!verifyCsrfRequest({ cookieHeader: ctx.req.headers.cookie, secret: deps.csrfSecret, submitted: form.get(CSRF_FIELD) })) {
+      throw new GuardError(403, "invalid CSRF token");
+    }
+  }
+
+  const renderList = async (): Promise<RouteResult> => {
+    const groups = groupsFromTuples(await pagedTuples(keto, { namespace: GROUP_NS, relation: MEMBERS }));
+    return { html: await render("admin/groups", { model: buildGroupsListModel({ csrfToken, groups, menu, url: ctx.url, user }) }) };
+  };
+  const renderForm = async (extra: { error?: string; values?: { member?: string; name?: string } }): Promise<RouteResult> => {
+    const { options } = await memberCandidates(keto, kratosAdmin);
+    return { html: await render("admin/group-form", { model: buildGroupFormModel({ csrfToken, memberOptions: options, menu, user, ...extra }) }) };
+  };
+  const renderDetail = async (name: string): Promise<RouteResult> => {
+    const { emailById, options } = await memberCandidates(keto, kratosAdmin);
+    const members = (await pagedTuples(keto, { namespace: GROUP_NS, object: name, relation: MEMBERS })).map((t) => memberView(t, emailById));
+    return { html: await render("admin/group-detail", { model: buildGroupDetailModel({ candidates: options, csrfToken, group: { name }, members, menu, user }) }) };
+  };
+
+  // /admin/groups — list (GET) · create (POST)
+  if (seg.length === 0) {
+    if (method === "GET") return renderList();
+    if (method === "POST") {
+      const name = (form!.get("name") ?? "").trim();
+      const tuple = memberTuple(name, (form!.get("member") ?? "").trim());
+      const reject = (error: string): Promise<RouteResult> =>
+        renderForm({ error, values: { member: form!.get("member") ?? "", name } }).then((r) => ({ ...r, status: 400 }));
+      if (!isValidGroupName(name)) return reject("Group names use lowercase letters, digits, dashes and underscores.");
+      if (!tuple) return reject("Pick a member to add as the group's first member.");
+      if (await groupExists(keto, name)) return reject("A group with that name already exists.");
+      await keto.writeTuple(tuple);
+      return { redirect: detailHref(name) };
+    }
+    return null;
+  }
+
+  // /admin/groups/new — create form
+  if (seg.length === 1 && seg[0] === "new" && method === "GET") return renderForm({});
+
+  // /admin/groups/:name …
+  const name = safeDecode(seg[0]!);
+  if (name === null || !isValidGroupName(name)) return { html: await render("404", { title: "Not found" }), status: 404 };
+  const base = detailHref(name);
+
+  if (seg.length === 1 && method === "GET") return renderDetail(name);
+
+  if (seg.length === 2 && seg[1] === "members" && method === "POST") {
+    const tuple = memberTuple(name, (form!.get("member") ?? "").trim());
+    // Skip an invalid member or a self-nest (the picker already excludes both).
+    if (tuple && tuple.subject_set?.object !== name) await keto.writeTuple(tuple);
+    return { redirect: base };
+  }
+  if (seg.length === 2 && seg[1] === "delete" && method === "POST") {
+    await keto.deleteTuple({ namespace: GROUP_NS, object: name, relation: MEMBERS }); // removes every member tuple
+    return { redirect: ADMIN_GROUPS_BASE };
+  }
+  if (seg.length === 3 && seg[1] === "members" && seg[2] === "delete" && method === "POST") {
+    const tuple = memberTuple(name, (form!.get("member") ?? "").trim());
+    if (tuple) await keto.deleteTuple(tuple);
+    return { redirect: base };
+  }
+  return null;
+}

src/admin-nav.ts

@@ -0,0 +1,23 @@
+// Shared sidebar nav for the built-in admin screens (todo §5). Both the Users and Groups
+// screens render the same admin section (Dashboard · Users · Groups), with `current` set on the
+// active item. Extracted so the two screens can't drift. The global config-driven menu wiring
+// (an admin section gated per user) is the separate §5 menu item; this is the local in-screen nav.
+
+import { type MenuConfig } from "./menu-config.ts";
+import { composeNav, type NavNode } from "./nav.ts";
+
+export const ADMIN_PERMISSION = "admin"; // role token gating every admin screen
+export const ADMIN_USERS_BASE = "/admin/users";
+export const ADMIN_GROUPS_BASE = "/admin/groups";
+
+type AdminScreen = "dashboard" | "groups" | "users";
+
+export function adminNav(roles: string[], menu: MenuConfig, current: AdminScreen): NavNode[] {
+  const gated = (id: AdminScreen, href: string, icon: string, label: string): NavNode =>
+    ({ ...(current === id ? { current: true } : {}), href, icon, id, label, permission: ADMIN_PERMISSION });
+  return composeNav([[
+    { href: "/", icon: "i-grid", id: "dashboard", label: "Dashboard" },
+    gated("users", ADMIN_USERS_BASE, "i-users", "Users"),
+    gated("groups", ADMIN_GROUPS_BASE, "i-layers", "Groups"),
+  ]], menu.override, roles);
+}

src/admin-users.ts

@@ -5,6 +5,7 @@
 // imperative shell app.ts dispatches to — it gates (admin only), CSRF-guards every mutation, and
 // maps each action to a RouteResult (render a page, or redirect after a write — PRG).
 
+import { ADMIN_PERMISSION, ADMIN_USERS_BASE, adminNav } from "./admin-nav.ts";
 import { readFormBody } from "./body.ts";
 import type { RequestContext, User } from "./context.ts";
 import { CSRF_FIELD, verifyCsrfRequest } from "./csrf.ts";
@@ -13,13 +14,10 @@ import type { Identity, KratosAdmin, RecoveryCode } from "./kratos-admin.ts";
 import { KratosError } from "./kratos-public.ts";
 import { parseListQuery } from "./list-query.ts";
 import { DEFAULT_MENU, type MenuConfig } from "./menu-config.ts";
-import { composeNav, type NavNode } from "./nav.ts";
 import { paginate } from "./paginate.ts";
 import type { RouteResult } from "./plugin.ts";
 import { buildShellContext } from "./shell-context.ts";
 
-export const ADMIN_USERS_BASE = "/admin/users";
-export const ADMIN_PERMISSION = "admin"; // role token gating every admin screen
 const SCHEMA_ID = "default"; // matches kratos.yml identity.default_schema_id
 const DEFAULT_PAGE_SIZE = 25;
 const PAGE_SIZES = [25, 50, 100];
@@ -106,13 +104,6 @@ const COLUMNS = [
   { key: "status", label: "Status" },
 ];
 
-function adminNav(roles: string[], menu: MenuConfig, currentId: string): NavNode[] {
-  return composeNav([[
-    { href: "/", icon: "i-grid", id: "dashboard", label: "Dashboard" },
-    { ...(currentId === "users" ? { current: true } : {}), href: ADMIN_USERS_BASE, icon: "i-users", id: "users", label: "Users", permission: ADMIN_PERMISSION },
-  ]], menu.override, roles);
-}
-
 // Canonical list URL from the current state + per-link overrides; omits defaults so links stay tidy.
 function listHref(state: ListState, overrides: Partial<ListState> = {}): string {
   const s = { ...state, ...overrides };

src/app.test.ts

@@ -10,7 +10,7 @@ import { createApp } from "./app.ts";
 import { CSRF_COOKIE, issueCsrfToken } from "./csrf.ts";
 import { can, check, GuardError, requireSession } from "./guards.ts";
 import { staticJwks } from "./jwks.ts";
-import type { KetoClient } from "./keto-client.ts";
+import type { KetoClient, RelationTuple, SubjectSet } from "./keto-client.ts";
 import type { Identity, KratosAdmin } from "./kratos-admin.ts";
 import { KratosError, type Flow, type FlowType, type KratosPublic, type Session, type UiNode } from "./kratos-public.ts";
 import { SESSION_COOKIE } from "./login.ts";
@@ -532,6 +532,90 @@ test("admin Users screen: gate, list/filter, create, edit, deactivate, delete, r
   assert.equal((await get(`/admin/users/${randomUUID()}`)).status, 404);
 });
 
+// Built-in Groups admin screen (§5): gate + list/create/membership/delete over HTTP against a
+// fake in-memory Keto (tuples are the only state) and a stub Kratos admin (resolves member emails).
+const sameSet = (a?: SubjectSet, b?: SubjectSet): boolean =>
+  (!a && !b) || (!!a && !!b && a.namespace === b.namespace && a.object === b.object && a.relation === b.relation);
+const matchesTuple = (t: RelationTuple, f: Partial<RelationTuple>): boolean =>
+  (f.namespace === undefined || t.namespace === f.namespace) &&
+  (f.object === undefined || t.object === f.object) &&
+  (f.relation === undefined || t.relation === f.relation) &&
+  (f.subject_id === undefined || t.subject_id === f.subject_id) &&
+  (f.subject_set === undefined || sameSet(t.subject_set, f.subject_set));
+
+test("admin Groups screen: gate, list, create, detail/membership, delete (CSRF-guarded)", async (t) => {
+  const ada = "01902d5e-7b6c-7e3a-9f21-3c8d1e0a4b01";
+  const grace = "01902d5e-7b6c-7e3a-9f21-3c8d1e0a4b02";
+  const identities: Identity[] = [
+    { id: ada, schema_id: "default", state: "active", traits: { email: "ada@example.com" } },
+    { id: grace, schema_id: "default", state: "active", traits: { email: "grace@example.com" } },
+  ];
+  const tuples: RelationTuple[] = [{ namespace: "Group", object: "eng", relation: "members", subject_id: `user:${ada}` }];
+  const keto: KetoClient = {
+    check: async () => false,
+    deleteTuple: async (f) => { for (let i = tuples.length - 1; i >= 0; i--) if (matchesTuple(tuples[i]!, f)) tuples.splice(i, 1); },
+    expand: async () => ({ type: "leaf" }),
+    listRelations: async (q = {}) => ({ nextPageToken: null, tuples: tuples.filter((t) => matchesTuple(t, q)) }),
+    writeTuple: async (tp) => { if (!tuples.some((t) => matchesTuple(t, tp) && sameSet(t.subject_set, tp.subject_set))) tuples.push(tp); },
+  };
+  const kratosAdmin = stubAdmin({ listIdentities: async () => ({ identities, nextPageToken: null }) });
+  const csrfSecret = "groups-secret";
+  const app = createApp({ csrfSecret, jwks: staticJwks([ecJwk]), keto, kratosAdmin });
+  await new Promise<void>((r) => app.listen(0, r));
+  t.after(() => app.close());
+  const url = `http://localhost:${(app.address() as AddressInfo).port}`;
+  const nowSec = Math.floor(Date.now() / 1000);
+  const token = issueCsrfToken(csrfSecret);
+  const cookie = (roles: string[]) => `${SESSION_COOKIE}=${mintJwt({ email: "admin@x", exp: nowSec + 600, roles, sub: "admin1" })}; ${CSRF_COOKIE}=${token}`;
+  const get = (path: string, roles: string[] = ["admin"]) => fetch(url + path, { headers: { cookie: cookie(roles) }, redirect: "manual" });
+  const post = (path: string, body: string) =>
+    fetch(url + path, { body, headers: { "content-type": "application/x-www-form-urlencoded", cookie: cookie(["admin"]) }, method: "POST", redirect: "manual" });
+
+  // Gate: anonymous → /login; a signed-in non-admin → 403.
+  const anon = await fetch(url + "/admin/groups", { redirect: "manual" });
+  assert.equal(anon.status, 303);
+  assert.equal(anon.headers.get("location"), "/login");
+  assert.equal((await get("/admin/groups", [])).status, 403);
+
+  // List: the existing group shows + the "add" link.
+  const listHtml = await (await get("/admin/groups")).text();
+  assert.match(listHtml, /href="\/admin\/groups\/eng"/);
+  assert.match(listHtml, /href="\/admin\/groups\/new"/);
+
+  // Create: the form renders; a valid post writes the first-member tuple and redirects to the detail.
+  assert.match(await (await get("/admin/groups/new")).text(), /Create group/);
+  const created = await post("/admin/groups", `_csrf=${token}&name=design&member=user:${grace}`);
+  assert.equal(created.status, 303);
+  assert.equal(created.headers.get("location"), "/admin/groups/design");
+  assert.ok(tuples.some((tp) => tp.object === "design" && tp.subject_id === `user:${grace}`));
+
+  // An invalid name, a duplicate name, or a missing CSRF token are all refused, nothing written.
+  const before = tuples.length;
+  assert.equal((await post("/admin/groups", `_csrf=${token}&name=Bad Name&member=user:${grace}`)).status, 400);
+  assert.equal((await post("/admin/groups", `_csrf=${token}&name=eng&member=user:${grace}`)).status, 400); // already exists
+  assert.equal((await post("/admin/groups", `name=x&member=user:${grace}`)).status, 403);
+  assert.equal(tuples.length, before);
+
+  // Detail: lists the current member by email.
+  assert.match(await (await get("/admin/groups/eng")).text(), /ada@example\.com/);
+
+  // Add a member, then remove it.
+  await post("/admin/groups/eng/members", `_csrf=${token}&member=user:${grace}`);
+  assert.ok(tuples.some((tp) => tp.object === "eng" && tp.subject_id === `user:${grace}`));
+  await post("/admin/groups/eng/members/delete", `_csrf=${token}&member=user:${grace}`);
+  assert.ok(!tuples.some((tp) => tp.object === "eng" && tp.subject_id === `user:${grace}`));
+
+  // Delete the group: removes every member tuple, back to the list.
+  const del = await post("/admin/groups/eng/delete", `_csrf=${token}`);
+  assert.equal(del.status, 303);
+  assert.equal(del.headers.get("location"), "/admin/groups");
+  assert.ok(!tuples.some((tp) => tp.object === "eng"));
+
+  // An invalid group name in the path → 404; malformed %-encoding doesn't 500.
+  assert.equal((await get("/admin/groups/Bad%20Name")).status, 404);
+  assert.equal((await get("/admin/groups/%ZZ")).status, 404);
+});
+
 test("resolveStaticPath blocks traversal and control chars, allows nested files", () => {
   assert.equal(resolveStaticPath("/srv/public", "../app.ts"), null);
   assert.equal(resolveStaticPath("/srv/public", "a\x00b"), null);

src/app.ts

@@ -3,7 +3,9 @@ import { createServer, type Server, type ServerResponse } from "node:http";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 import * as ejs from "ejs";
-import { ADMIN_USERS_BASE, type AdminUsersDeps, handleAdminUsers } from "./admin-users.ts";
+import { ADMIN_GROUPS_BASE, ADMIN_USERS_BASE } from "./admin-nav.ts";
+import { type AdminGroupsDeps, handleAdminGroups } from "./admin-groups.ts";
+import { type AdminUsersDeps, handleAdminUsers } from "./admin-users.ts";
 import { readFormBody } from "./body.ts";
 import { buildContext, type User } from "./context.ts";
 import { CSRF_FIELD, csrfCookie, ensureCsrfToken, verifyCsrfRequest } from "./csrf.ts";
@@ -72,9 +74,11 @@ export function createApp(options: AppOptions = {}): Server {
   // building-block partials (resolved from viewsDir) and their own partials/subfolders.
   const renderView = renderPluginView({ cache, coreViewsDir: viewsDir, pluginsDir });
 
-  // Built-in admin screens (§5) — wired only when the Kratos admin client is present (the writes
-  // go there). They render core views via `render` and are gated/CSRF-guarded inside the handler.
+  // Built-in admin screens (§5) — wired only when their Ory clients are present (the writes go
+  // there). They render core views via `render` and are gated/CSRF-guarded inside the handler.
+  // Users writes to Kratos; Groups writes to Keto and reads users from Kratos for the pickers.
   const adminDeps: AdminUsersDeps | null = kratosAdmin ? { csrfSecret, kratosAdmin, menu, render } : null;
+  const adminGroupsDeps: AdminGroupsDeps | null = kratosAdmin && keto ? { csrfSecret, keto, kratosAdmin, menu, render } : null;
 
   const sendHtml = (res: ServerResponse, status: number, html: string): void => {
     res.writeHead(status, { "content-type": "text/html; charset=utf-8" });
@@ -143,9 +147,9 @@ export function createApp(options: AppOptions = {}): Server {
         return;
       }
 
-      // Built-in Users admin screens (§5). The handler gates (admin only; throws GuardError the
-      // catch maps), CSRF-guards mutations, and returns html/redirect. Set the page's CSRF cookie
-      // when freshly minted (its forms carry the matching token); null ⇒ unknown subpath → 404.
+      // Built-in admin screens (§5). Each handler gates (admin only; throws GuardError the catch
+      // maps), CSRF-guards mutations, and returns html/redirect. Set the page's CSRF cookie when
+      // freshly minted (its forms carry the matching token); null ⇒ unknown subpath → 404.
       if (adminDeps && pathname.startsWith(ADMIN_USERS_BASE)) {
         const result = await handleAdminUsers(ctx, csrf.token, adminDeps);
         if (result) {
@@ -154,6 +158,14 @@ export function createApp(options: AppOptions = {}): Server {
           return;
         }
       }
+      if (adminGroupsDeps && pathname.startsWith(ADMIN_GROUPS_BASE)) {
+        const result = await handleAdminGroups(ctx, csrf.token, adminGroupsDeps);
+        if (result) {
+          if (csrf.fresh) res.appendHeader("set-cookie", csrfCookie(csrf.token, { secure: secureCookies }));
+          await sendResult(res, result, () => Promise.reject(new Error("admin screens return html, not view")));
+          return;
+        }
+      }
 
       // Themed Kratos self-service pages (login/registration/recovery/verification/settings).
       const flowType = AUTH_FLOWS[pathname];

src/data-table.test.ts

@@ -68,6 +68,13 @@ test("data-table renders sortable headers, row-select, typed cells, badges and k
   assert.match(html, /<div class="menu-sep"><\/div><button class="menu-item danger" type="button"><svg class="ico"><use href="#i-trash"\s*\/?><\/svg>Delete<\/button>/);
 });
 
+test("data-table rowHeader cell is a <th scope=row> identifier — a link when given href, else plain text", async () => {
+  const linked = flat(await render({ columns: [{ label: "Group" }], rows: [{ cells: [{ rowHeader: { href: "/admin/groups/eng", text: "eng" } }] }] }));
+  assert.match(linked, /<th scope="row"><a class="cell-strong" href="\/admin\/groups\/eng">eng<\/a><\/th>/);
+  const plain = flat(await render({ columns: [{ label: "Group" }], rows: [{ cells: [{ rowHeader: { text: "eng" } }] }] }));
+  assert.match(plain, /<th scope="row"><span class="cell-strong">eng<\/span><\/th>/);
+});
+
 test("data-table renders a minimal table (plain string cells, no select/actions) and never throws", async () => {
   const html = flat(await render({ columns: [{ label: "Name" }], rows: [{ cells: ["Plain"] }] }));
   assert.match(html, /<table class="table"><thead><tr><th scope="col">Name<\/th><\/tr><\/thead><tbody><tr><td>Plain<\/td><\/tr><\/tbody><\/table>/);