feat(auth): wire getAdminUser() to Auth.js v5 Google sign-in

After a user signs in with Google, they land on /admin but see
'Your account does not have admin access' because getAdminUser()
only checked the legacy dev_session and rc_auth_uid cookies.

This completes the Auth.js path:

- New src/lib/db.ts: shared pg.Pool singleton (extracted from
  src/lib/auth.ts). The single connection pool for the whole app
  — server actions, API routes, and Auth.js all import from here.

- src/lib/auth.ts: imports the shared pool, signIn event now calls
  the new upsert_admin_user_for_authjs RPC (idempotent) to
  auto-create a platform_admin row on first sign-in.

- New supabase/migrations/209_authjs_auto_create_admin.sql:
  - Defensive ALTER TABLE ADD COLUMN IF NOT EXISTS for
    can_manage_settings (was likely dashboard-added, not in any
    tracked migration)
  - SECURITY DEFINER RPC upsert_admin_user_for_authjs(p_user_id UUID)
    that inserts a platform_admin row with all permissions true
    and ON CONFLICT (user_id) DO NOTHING
  - NOTIFY pgrst to reload PostgREST schema cache

- src/lib/admin-permissions.ts: new Auth.js session check between
  dev_session and rc_auth_uid. Uses auth() from @/lib/auth to
  decrypt the JWT cookie server-side, then getAdminUserFromPool()
  queries admin_users + admin_user_brands via the shared pool.
  Legacy rc_auth_uid path unchanged (deferred).

- src/middleware.ts: recognizes Auth.js session cookies
  (authjs.session-token and __Secure-authjs.session-token) at the
  edge so signed-in users aren't bounced to /login.

Flow after this change:
  Dev/demo:  visit /admin → middleware auto-issues dev_session → in
  Prod:      click Google → Auth.js OAuth → signIn event creates
             admin_users row → redirect to /admin → getAdminUser()
             reads JWT, queries pool, returns platform_admin.

src/lib/admin-permissions.ts

@@ -1,4 +1,6 @@
 import { cookies } from "next/headers";
+import { auth } from "@/lib/auth";
+import { pool } from "@/lib/db";
 import type { AdminUser } from "./admin-permissions-types";
 export type { AdminUser } from "./admin-permissions-types";
 
@@ -8,7 +10,9 @@ export type { AdminUser } from "./admin-permissions-types";
  * Resolution order:
  *   1. Mock data mode (NEXT_PUBLIC_USE_MOCK_DATA=true) → platform_admin dev.
  *   2. `dev_session` cookie → dev admin (platform_admin/brand_admin/store_employee).
- *   3. Real auth (rc_auth_uid or rc_uid cookie) → load admin_users + brand_ids.
+ *   3. Auth.js v5 session (JWT cookie) → look up `admin_users` by the
+ *      Auth.js user id (the `users.id` UUID managed by @auth/pg-adapter).
+ *   4. Real auth (rc_auth_uid or rc_uid cookie) → load admin_users + brand_ids.
  *
  * `brand_id` is the active brand; `brand_ids` is the full membership list.
  * For dev sessions without a real DB, `brand_ids` is populated by:
@@ -24,12 +28,23 @@ export async function getAdminUser(): Promise<AdminUser | null> {
     return buildDevAdmin("platform_admin");
   }
 
-  // ── Dev session bypass (enabled for testing on all envs) ──────────────
+  // ── Dev session bypass (enabled for testing on all envs) ──────────
   const dev = cookieStore.get("dev_session")?.value;
   if (dev === "platform_admin" || dev === "brand_admin" || dev === "store_employee") {
     return buildDevAdmin(dev);
   }
 
+  // ── Auth.js v5 session (JWT) ─────────────────────────────────────
+  // After Google sign-in, the encrypted JWT cookie is set. `auth()`
+  // decrypts it server-side and returns the session — no DB call here,
+  // just cookie decryption. Then we look up the admin row by the
+  // Auth.js `users.id` UUID (same ID space as `admin_users.user_id`).
+  const session = await auth();
+  if (session?.user?.id) {
+    const admin = await getAdminUserFromPool(session.user.id);
+    if (admin) return admin;
+  }
+
   // ── Main auth: rc_auth_uid (new) or rc_uid (legacy) cookie set by /api/login ─
   const uid = cookieStore.get("rc_auth_uid")?.value ?? cookieStore.get("rc_uid")?.value;
   if (!uid) return null;
@@ -91,6 +106,49 @@ export async function getAdminUser(): Promise<AdminUser | null> {
   return buildAdminUser(admin, brandIds);
 }
 
+/**
+ * Look up an admin user by the Auth.js `users.id` UUID using the shared
+ * `pg` pool. Returns `null` if no active row exists.
+ *
+ * The `admin_users.user_id` column is UUID (see 028_fix_caller_uid_type.sql).
+ * The Auth.js `users.id` is also UUID (see 204_authjs_tables.sql:18). The
+ * @auth/pg-adapter auto-generates a fresh UUID per new user on first
+ * sign-in; the Google `sub` claim is stored separately in
+ * `accounts."providerAccountId"`. So both IDs are in the same UUID space.
+ */
+async function getAdminUserFromPool(userId: string): Promise<AdminUser | null> {
+  try {
+    const { rows } = await pool.query<Record<string, unknown>>(
+      "SELECT * FROM admin_users WHERE user_id = $1 AND active = true LIMIT 1",
+      [userId]
+    );
+    if (rows.length === 0) return null;
+    const admin = rows[0];
+    const brandIds = await fetchAdminUserBrandIdsFromPool(admin.id as string);
+    return buildAdminUser(admin, brandIds);
+  } catch (e) {
+    console.warn("[admin-permissions] getAdminUserFromPool error:", e);
+    return null;
+  }
+}
+
+/**
+ * Load `brand_ids` from the admin_user_brands junction for the given
+ * admin row id, via the shared `pg` pool. Returns an empty array on any
+ * failure.
+ */
+async function fetchAdminUserBrandIdsFromPool(adminRowId: string): Promise<string[]> {
+  try {
+    const { rows } = await pool.query<{ brand_id: string }>(
+      "SELECT brand_id FROM admin_user_brands WHERE admin_user_id = $1",
+      [adminRowId]
+    );
+    return rows.map((r) => r.brand_id).filter((id): id is string => typeof id === "string");
+  } catch {
+    return [];
+  }
+}
+
 /**
  * Load `brand_ids` from the admin_user_brands junction for the given admin row.
  * Returns an empty array on any failure (e.g. before migration 207 is applied).

src/lib/auth.ts

@@ -1,11 +1,8 @@
 import NextAuth from "next-auth";
 import PostgresAdapter from "@auth/pg-adapter";
-import { Pool } from "pg";
 import Credentials from "next-auth/providers/credentials";
-import {
-  authConfig,
-  isDevLoginEnabled,
-} from "@/auth.config";
+import { pool } from "@/lib/db";
+import { authConfig, isDevLoginEnabled } from "@/auth.config";
 
 /**
  * Build the dev Credentials provider. Lives here (Node-only) because
@@ -39,51 +36,11 @@ function buildDevCredentialsProvider() {
   });
 }
 
-/**
- * Shared Postgres pool for Auth.js. Reuses the same database the rest of
- * the app talks to (via `pg`). Lives behind a module-level singleton so
- * Next.js hot reload doesn't open a new pool on every request.
- *
- * Note: in production, `DATABASE_URL` should be the only DB env var. The
- * Supabase project URL / service role key are no longer required for auth
- * (they are still used elsewhere until the rest of the app is migrated off
- * the @supabase client — see CLAUDE.md).
- */
-const globalForPool = globalThis as unknown as { __pgPool?: Pool };
-
-function getPool(): Pool {
-  if (globalForPool.__pgPool) return globalForPool.__pgPool;
-
-  const connectionString =
-    process.env.DATABASE_URL ??
-    process.env.SUPABASE_DB_URL ??
-    process.env.POSTGRES_URL;
-
-  if (!connectionString) {
-    // Don't throw at module load — let route handlers return a clean 500
-    // if env is missing. The smoke test instructions tell the user to
-    // set DATABASE_URL.
-    // eslint-disable-next-line no-console
-    console.warn(
-      "[auth] No DATABASE_URL / SUPABASE_DB_URL / POSTGRES_URL set — Auth.js database adapter will not be wired up."
-    );
-  }
-
-  const pool = new Pool({
-    connectionString,
-    // Reasonable defaults; override via connection string if you need more
-    max: 10,
-    idleTimeoutMillis: 30_000,
-  });
-  globalForPool.__pgPool = pool;
-  return pool;
-}
-
 /**
  * Final server-side Auth.js config.
  *
  * Builds on `authConfig` (edge-safe) and layers on:
- *   1. The Postgres database adapter
+ *   1. The Postgres database adapter (uses the shared `pool` from @/lib/db)
  *   2. The dev Credentials provider (only in development)
  *
  * Note: when using a database adapter the session strategy is fixed to
@@ -96,7 +53,7 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
   // must use JWT. The Postgres adapter is still wired up so that user
   // records are created/updated when a new OAuth sign-in happens — but
   // the session itself is stored in the cookie as an encrypted JWT.
-  adapter: PostgresAdapter(getPool()),
+  adapter: PostgresAdapter(pool),
   // `session.strategy` is inherited from `authConfig` ("jwt")
   providers: [
     // Re-declare the providers from authConfig and append the dev
@@ -108,27 +65,23 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
   events: {
     /**
      * First-time sign-in: auto-create a `platform_admin` row in
-     * `admin_users` keyed to this auth.js user id, mirroring the legacy
-     * `rc_auth_uid` flow. This is the seam between the new auth layer
-     * and the existing admin authorization model.
+     * `admin_users` keyed to this Auth.js user id. The RPC is
+     * idempotent (ON CONFLICT DO NOTHING) so repeat sign-ins are no-ops.
+     *
+     * This is the seam between the new Auth.js auth layer and the
+     * existing admin authorization model. After this fires, the user
+     * is recognized by `getAdminUser()` in `src/lib/admin-permissions.ts`.
      */
     async signIn({ user }) {
       try {
-        const pool = getPool();
         const userId = user.id;
         if (!userId) return;
-        // Fire and forget — don't block sign-in on a missing admin_users row.
         await pool.query(
-          `SELECT id FROM admin_users WHERE user_id = $1 LIMIT 1`,
+          "SELECT * FROM upsert_admin_user_for_authjs($1)",
           [userId]
         );
-        // Note: we don't auto-create here; the existing `getAdminUser()`
-        // in `src/lib/admin-permissions.ts` is the source of truth for
-        // role lookups and is unchanged. After this migration the user
-        // is authenticated; the existing `dev_session` demo path still
-        // works for the smoke test.
       } catch (e) {
-        // eslint-disable-next-line no-console
+        // Don't block sign-in on a missing admin_users row.
         console.warn("[auth] signIn event error (non-fatal):", e);
       }
     },

src/lib/db.ts

@@ -0,0 +1,49 @@
+import { Pool } from "pg";
+
+/**
+ * Shared `pg.Pool` for direct Postgres access.
+ *
+ * This is the single connection pool for the entire app — server actions,
+ * API routes, and Auth.js all import `pool` from here. No more ad-hoc pools
+ * in individual files.
+ *
+ * Replaces the Supabase JS client (see CLAUDE.md "Supabase is being
+ * removed in favor of a direct Postgres connection"). SECURITY DEFINER
+ * RPCs are the recommended way to do reads/writes; this pool is the
+ * transport.
+ *
+ * Connection resolution:
+ *   1. `DATABASE_URL` — preferred, single connection string
+ *   2. `SUPABASE_DB_URL` — legacy, for projects still on Supabase
+ *   3. `POSTGRES_URL` — alternative
+ *
+ * Singleton pattern: `globalThis.__pgPool` so Next.js hot reload doesn't
+ * open a new pool on every request.
+ */
+
+const globalForPool = globalThis as unknown as { __pgPool?: Pool };
+
+function createPool(): Pool {
+  const connectionString =
+    process.env.DATABASE_URL ??
+    process.env.SUPABASE_DB_URL ??
+    process.env.POSTGRES_URL;
+
+  if (!connectionString) {
+    // Don't throw at module load — let route handlers return a clean 500
+    // if env is missing. The deploy workflow and `.env.example` document
+    // the required vars.
+    console.warn(
+      "[db] No DATABASE_URL / SUPABASE_DB_URL / POSTGRES_URL set — pg pool will fail on first query."
+    );
+  }
+
+  return new Pool({
+    connectionString,
+    max: 10,
+    idleTimeoutMillis: 30_000,
+  });
+}
+
+export const pool: Pool =
+  globalForPool.__pgPool ?? (globalForPool.__pgPool = createPool());

src/middleware.ts

@@ -3,18 +3,18 @@ import { NextResponse, type NextRequest } from "next/server";
 /**
  * Middleware for /admin/* and /login routes.
  *
- * Two responsibilities:
- *   1. Gate /admin/* — only authenticated users (by dev_session, rc_auth_uid,
- *      or rc_uid cookie) can access. Unauthenticated users are redirected
- *      to /login.
- *   2. Demo / dev auto-login — when ALLOW_DEV_LOGIN is enabled (on by
+ * Recognises three auth sources at the edge:
+ *   1. Auth.js v5 JWT cookie (`authjs.session-token` or the `__Secure-`
+ *      variant in prod) — set after Google sign-in.
+ *   2. `dev_session`, `rc_auth_uid`, `rc_uid` — legacy / dev cookies.
+ *   3. Demo / dev auto-login — when ALLOW_DEV_LOGIN is enabled (on by
  *      default in non-prod) and the user has no auth cookie, automatically
  *      issue `dev_session=platform_admin` so visiting /admin just works.
  *      No buttons, no demo page, no client-side cookie games.
  *
  * This is the single source of truth for "am I allowed in?" at the edge.
- * The page-level `getAdminUser()` re-checks the same cookies, so the two
- * stay in sync.
+ * The page-level `getAdminUser()` re-checks the same cookies (and reads
+ * the Auth.js JWT) to resolve the role.
  */
 export function middleware(request: NextRequest) {
   const { nextUrl } = request;
@@ -25,12 +25,20 @@ export function middleware(request: NextRequest) {
   const dev = request.cookies.get("dev_session")?.value;
   const rcAuthUid = request.cookies.get("rc_auth_uid")?.value;
   const rcUid = request.cookies.get("rc_uid")?.value;
+  // Auth.js v5 sets an encrypted JWT cookie. Names differ by transport:
+  //   `authjs.session-token` (dev / HTTP) and `__Secure-authjs.session-token`
+  //   (prod / HTTPS). The presence of either cookie is sufficient to
+  //   consider the request authenticated at the edge — the page-level
+  //   `getAdminUser()` re-reads the JWT and resolves the role.
+  const authJsSessionToken = request.cookies.get("authjs.session-token")?.value;
+  const authJsSecureToken = request.cookies.get("__Secure-authjs.session-token")?.value;
   const hasDevSession =
     dev === "platform_admin" ||
     dev === "brand_admin" ||
     dev === "store_employee";
   const hasRealAuth = Boolean(rcAuthUid || rcUid);
-  const isAuthenticated = hasDevSession || hasRealAuth;
+  const hasAuthJsSession = Boolean(authJsSessionToken || authJsSecureToken);
+  const isAuthenticated = hasDevSession || hasRealAuth || hasAuthJsSession;
 
   // ── /admin/* ──────────────────────────────────────────────────────
   if (isOnAdmin) {