docs: multi-brand admin support design spec

Adds a design document for supporting admins who manage 2+ specific brands (e.g., franchise / multi-brand tenant use cases). Current model: admin_users.brand_id is a single UUID | null, and the effectiveBrandId = brandId ?? adminUser.brand_id ?? null pattern silently does the wrong thing for multi-brand admins. There is no central validation that an admin is acting in a brand they have access to. Proposed: admin_user_brands junction table (m:n), kept admin_users.brand_id for backwards compat, a new multi_brand_admin role, a cookie-based active brand, a centralized brand-scope helper, and a BrandSelector dropdown in the admin header. ~30 server actions and ~10 page server components get a mechanical one-line swap to use the new helper. Follow-up migration 220_drop_legacy_brand_id.sql will drop the legacy column after we verify nothing reads it. Out of scope for this spec. See docs/superpowers/specs/2026-06-04-multi-brand-admin-design.md
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+# Multi-Brand Admin Support
+
+**Date:** 2026-06-04
+**Status:** Draft → Approved
+**Author:** Grok (brainstorming session)
+**Migration file:** `supabase/migrations/204_multi_brand_admin.sql`
+**Follow-up migration (out of scope):** `220_drop_legacy_brand_id.sql`
+
+## Problem
+
+`admin_users.brand_id` is a single `UUID | null`. The platform supports a `platform_admin` role (no brand) and a `brand_admin` role (one brand). There is no representation for an admin who legitimately needs access to 2+ specific brands — e.g., a parent company operating multiple storefronts with shared operations staff.
+
+The current `effectiveBrandId = brandId ?? adminUser.brand_id ?? null` pattern silently does the wrong thing for multi-brand use cases:
+
+- Data model can't represent "Jane is admin for Brand A AND Brand B" — would require two `admin_users` rows (and the auth-user→admin-user join gets messy).
+- No central validation that an admin is acting in a brand they actually have access to.
+- No persistent "current brand" context — every page re-derives it from scratch.
+- No per-brand permission overrides possible (locks in flexibility for the future).
+
+This spec addresses multi-brand tenants / franchises: same staff managing multiple brands under a parent org, where brands are separate for storefront/billing but share operations.
+
+## Goals
+
+- An admin can be associated with multiple brands via a junction table.
+- A persistent "active brand" is stored in a cookie, switchable via UI, and used as the default when no explicit brand is requested.
+- A new `multi_brand_admin` role makes the relationship explicit in the data and the UI.
+- `platform_admin` continues to work unchanged (gets all brands implicitly).
+- Existing single-brand `brand_admin`, `store_employee`, and `staff` users continue to work with zero behavior change.
+- Server actions get a single, central place to resolve and validate the active brand.
+
+## Non-Goals (YAGNI)
+
+- Per-(admin, brand) permission overrides. The user explicitly chose "same perms across all brands."
+- Brand-group / parent-org concept. The junction table makes this possible later, but it's not built now.
+- "Last accessed brand" auto-redirect. The cookie is the source of truth; no extra logic.
+- UI for managing `admin_user_brands` rows. Use Supabase Studio or a follow-up admin UI PR.
+- Dropping the legacy `admin_users.brand_id` column. A follow-up migration `220_drop_legacy_brand_id.sql` will do this after we verify nothing reads it. Out of scope for this spec.
+
+## Approach: Junction Table + Backwards-Compat `brand_id`
+
+Selected from among three options:
+
+| Option | Why not |
+|---|---|
+| A. Junction + keep `brand_id` (selected) | — |
+| B. Junction only, drop `brand_id` | High migration risk; every server action reference must change. |
+| C. `brand_ids UUID[]` on `admin_users` | No FK, awkward reverse lookups, locks out per-brand metadata. |
+
+A is the lowest-risk additive path that solves the problem.
+
+## Data Model
+
+### New table: `admin_user_brands`
+
+```sql
+CREATE TABLE admin_user_brands (
+  admin_user_id UUID NOT NULL REFERENCES admin_users(id) ON DELETE CASCADE,
+  brand_id      UUID NOT NULL REFERENCES brands(id)     ON DELETE CASCADE,
+  added_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  added_by      UUID REFERENCES admin_users(id),
+  PRIMARY KEY (admin_user_id, brand_id)
+);
+CREATE INDEX admin_user_brands_brand_id_idx ON admin_user_brands(brand_id);
+```
+
+- Composite PK enforces uniqueness.
+- Index on `brand_id` makes "which admins are in Brand X?" queries fast.
+- `added_at` / `added_by` for audit trail.
+- `ON DELETE CASCADE` for both FKs — deleting an admin or brand cleans up the junction.
+
+### New role: `multi_brand_admin`
+
+Added to the `role` CHECK constraint. Functionally equivalent to `brand_admin` permission-wise — same `can_manage_*` flags apply. The role label disambiguates intent in the UI ("this person manages 3 brands" vs "this person manages 1 brand") and in audit logs.
+
+### Updated `AdminUser` type
+
+```ts
+// src/lib/admin-permissions-types.ts
+export type AdminUser = {
+  // ... existing fields
+  brand_id: string | null;    // active brand (one of brand_ids, or null for platform_admin)
+  brand_ids: string[];        // all brands this admin can act in
+  role: "platform_admin" | "brand_admin" | "multi_brand_admin" | "store_employee" | "staff";
+};
+```
+
+### Membership rules
+
+| Role | `brand_id` (active) | `brand_ids` (membership) |
+|---|---|---|
+| `platform_admin` | `null` (or cookie-selected brand) | Implicitly all brands; `brand_ids` populated by `listBrandsForAdmin` querying the `brands` table |
+| `multi_brand_admin` | First/selected brand | 2+ brands from `admin_user_brands` |
+| `brand_admin` | Their single brand | `[that one brand]` |
+| `store_employee` | Their single brand | `[that one brand]` |
+| `staff` | Their single brand | `[that one brand]` |
+
+For `platform_admin`, the application layer short-circuits brand-access checks (`if (adminUser.role === "platform_admin") return ...`). The `brand_ids` field is only used by `listBrandsForAdmin` to render the dropdown options; it is not used for permission gating for `platform_admin`.
+
+### `getAdminUser()` resolution order
+
+1. If `dev_session` cookie set → return dev admin. For `platform_admin` dev: `brand_id: null, brand_ids: []` (resolved against `brands` table by `listBrandsForAdmin`). For `store_employee` dev: `brand_id: <first-real-brand-id>, brand_ids: [<that-id>]` — fetched from the `brands` table so dev store_employee can browse a real brand's data. (If no brands exist, dev store_employee sees `<AdminAccessDenied />` — known limitation.)
+2. If `NEXT_PUBLIC_USE_MOCK_DATA=true` → same as `platform_admin` dev.
+3. Real auth → load `admin_users` row, then JOIN `admin_user_brands` to populate `brand_ids`.
+4. Set `brand_id` from (in order): `active_brand_id` cookie (if in `brand_ids` for non-platform-admin, or always for platform-admin) → `admin_users.brand_id` (if in `brand_ids`) → first of `brand_ids`.
+
+## Server Action Patterns
+
+### New file: `src/lib/brand-scope.ts`
+
+```ts
+import { cookies } from "next/headers";
+import type { AdminUser } from "./admin-permissions-types";
+
+const ACTIVE_BRAND_COOKIE = "active_brand_id";
+
+export async function getActiveBrandId(
+  adminUser: AdminUser,
+  requested?: string | null
+): Promise<string | null> {
+  // Cookie is the source of truth for "what brand am I acting in right now"
+  // for everyone — including platform_admin (who can pin a specific brand
+  // or fall back to null = "all brands").
+  const cookieStore = await cookies();
+  const cookieBrand = cookieStore.get(ACTIVE_BRAND_COOKIE)?.value ?? null;
+
+  if (adminUser.role === "platform_admin") {
+    // requested > cookie > null (all brands)
+    return requested ?? cookieBrand ?? null;
+  }
+
+  // Non-platform-admin: requested (if in brand_ids) > cookie (if in brand_ids) > adminUser.brand_id
+  if (requested) {
+    return adminUser.brand_ids.includes(requested) ? requested : null;
+  }
+  if (cookieBrand && adminUser.brand_ids.includes(cookieBrand)) {
+    return cookieBrand;
+  }
+  return adminUser.brand_id;
+}
+
+export async function setActiveBrandCookie(brandId: string): Promise<void> {
+  const cookieStore = await cookies();
+  cookieStore.set(ACTIVE_BRAND_COOKIE, brandId, {
+    httpOnly: true,
+    sameSite: "lax",
+    path: "/",
+    maxAge: 60 * 60 * 24 * 30, // 30 days
+  });
+}
+
+export async function clearActiveBrandCookie(): Promise<void> {
+  const cookieStore = await cookies();
+  cookieStore.delete(ACTIVE_BRAND_COOKIE);
+}
+
+export function assertBrandAccess(adminUser: AdminUser, brandId: string): void {
+  if (adminUser.role === "platform_admin") return;
+  if (!adminUser.brand_ids.includes(brandId)) {
+    throw new Error("Brand access denied");
+  }
+}
+```
+
+### Server action: set active brand
+
+```ts
+// src/actions/admin/set-active-brand.ts
+"use server";
+import { getAdminUser } from "@/lib/admin-permissions";
+import { setActiveBrandCookie, clearActiveBrandCookie } from "@/lib/brand-scope";
+
+export async function setActiveBrand(brandId: string | null): Promise<{ success: boolean; error?: string }> {
+  const adminUser = await getAdminUser();
+  if (!adminUser) return { success: false, error: "Not authenticated" };
+
+  // null = "All brands" (platform_admin only)
+  if (brandId === null) {
+    if (adminUser.role !== "platform_admin") {
+      return { success: false, error: "Only platform admins can select 'All brands'" };
+    }
+    await clearActiveBrandCookie();
+    return { success: true };
+  }
+
+  if (adminUser.role !== "platform_admin" && !adminUser.brand_ids.includes(brandId)) {
+    return { success: false, error: "No access to that brand" };
+  }
+  await setActiveBrandCookie(brandId);
+  return { success: true };
+}
+```
+
+### New server function: list brands for admin
+
+```ts
+// src/actions/brands.ts
+import { getAdminUser } from "@/lib/admin-permissions";
+import { svcHeaders } from "@/lib/svc-headers";
+
+export async function listBrandsForAdmin(): Promise<
+  { id: string; name: string; slug: string; logo_url: string | null }[]
+> {
+  const adminUser = await getAdminUser();
+  if (!adminUser) return [];
+
+  const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL!;
+  const serviceKey = process.env.SUPABASE_SERVICE_ROLE_KEY!;
+
+  if (adminUser.role === "platform_admin") {
+    const res = await fetch(
+      `${supabaseUrl}/rest/v1/brands?select=id,name,slug,logo_url&order=name`,
+      { headers: svcHeaders(serviceKey) }
+    );
+    return res.ok ? await res.json() : [];
+  }
+
+  if (adminUser.brand_ids.length === 0) return [];
+
+  const filter = `id=in.(${adminUser.brand_ids.map((id) => `"${id}"`).join(",")})`;
+  const res = await fetch(
+    `${supabaseUrl}/rest/v1/brands?${filter}&select=id,name,slug,logo_url&order=name`,
+    { headers: svcHeaders(serviceKey) }
+  );
+  return res.ok ? await res.json() : [];
+}
+```
+
+### Server action migration pattern
+
+```ts
+// Before:
+const effectiveBrandId = brandId ?? adminUser.brand_id ?? null;
+
+// After:
+import { getActiveBrandId } from "@/lib/brand-scope";
+
+const activeBrandId = await getActiveBrandId(adminUser, brandId);
+if (!activeBrandId && adminUser.role !== "platform_admin") {
+  return { success: false, error: "Brand access required" };
+}
+const effectiveBrandId = activeBrandId;
+```
+
+This is a mechanical one-line swap in ~30 server actions identified by the grep:
+
+- `src/actions/wholesale.ts` (multiple)
+- `src/actions/products.ts`
+- `src/actions/communications/templates.ts`
+- `src/actions/communications/campaigns.ts`
+- `src/actions/orders/create-admin-order.ts`
+- `src/actions/stops.ts`
+- `src/actions/analytics.ts`
+- `src/actions/square-sync-ui.ts`
+- `src/actions/shipping.ts`
+- `src/actions/payments.ts`
+- `src/actions/ai-import.ts`
+- `src/actions/wholesale-register.ts`
+
+### Page server component pattern
+
+```ts
+// Before (src/app/admin/orders/page.tsx):
+const effectiveBrandId = brandIdParam ?? adminUser.brand_id ?? "";
+
+// After:
+import { getActiveBrandId } from "@/lib/brand-scope";
+
+export default async function AdminOrdersPage() {
+  const adminUser = await getAdminUser();
+  if (!adminUser) return <AdminAccessDenied />;
+
+  const activeBrandId = await getActiveBrandId(adminUser, brandIdParam);
+
+  if (!activeBrandId && adminUser.role !== "platform_admin") {
+    return <AdminAccessDenied />;
+  }
+
+  // ... rest of the page
+}
+```
+
+This applies to every page under `src/app/admin/` — including the existing `/admin/taxes/[brandId]` and `/admin/settings/billing/[brandId]` which already do brand param resolution.
+
+## UI Components
+
+### Brand selector
+
+**Location:** `src/components/admin/AdminHeader.tsx` (the top bar already rendered on every `/admin/*` page).
+
+**Behavior:** A dropdown showing:
+- Brand logo + name (current active brand)
+- Chevron
+- "All brands" option at the top (only for `platform_admin`)
+- List of accessible brands (`adminUser.brand_ids`)
+- Small badge "Multi-brand manager" next to the user's name when `role === "multi_brand_admin"`
+
+**Visibility matrix:**
+
+| Admin | Show dropdown? | Options |
+|---|---|---|
+| `platform_admin` | Yes | "All brands" + list of all brands |
+| `multi_brand_admin` (2+ brands) | Yes | List of their brands |
+| `brand_admin` / `store_employee` / `staff` (1 brand) | No | — |
+| `platform_admin` (dev_session) | Yes | "All brands" + list of all brands (same UX as production) |
+
+**On select:**
+
+```ts
+// src/components/admin/BrandSelector.tsx (client component)
+"use client";
+async function handleSelect(brandId: string | null) {
+  await setActiveBrand(brandId); // null = "All brands"
+  router.refresh();
+}
+```
+
+`router.refresh()` re-runs server components and re-reads the cookie, so all data on the current page reloads in the new brand context. The URL is **not** changed — the cookie is the source of truth for "what brand am I acting in right now."
+
+### URL-level brand params
+
+Keep URL-level brand as-is — URLs are shareable links. The resolution order for the `brandId` param passed to `getActiveBrandId` is:
+
+1. URL `brandId` param (if present)
+2. `active_brand_id` cookie
+3. `adminUser.brand_id` (legacy single brand)
+4. First of `adminUser.brand_ids`
+5. (platform_admin only) `null` → "all brands"
+
+## Migration: `supabase/migrations/204_multi_brand_admin.sql`
+
+```sql
+-- 1. Add multi_brand_admin to role CHECK constraint
+ALTER TABLE admin_users DROP CONSTRAINT IF EXISTS admin_users_role_check;
+ALTER TABLE admin_users ADD CONSTRAINT admin_users_role_check
+  CHECK (role IN ('platform_admin', 'brand_admin', 'multi_brand_admin', 'store_employee', 'staff'));
+
+-- 2. Create junction table
+CREATE TABLE admin_user_brands (
+  admin_user_id UUID NOT NULL REFERENCES admin_users(id) ON DELETE CASCADE,
+  brand_id      UUID NOT NULL REFERENCES brands(id)     ON DELETE CASCADE,
+  added_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  added_by      UUID REFERENCES admin_users(id),
+  PRIMARY KEY (admin_user_id, brand_id)
+);
+CREATE INDEX admin_user_brands_brand_id_idx ON admin_user_brands(brand_id);
+
+-- 3. Backfill from existing brand_id (single-brand admins)
+INSERT INTO admin_user_brands (admin_user_id, brand_id)
+SELECT id, brand_id FROM admin_users
+WHERE brand_id IS NOT NULL
+ON CONFLICT DO NOTHING;
+
+-- 4. Promote anyone with > 1 brand to multi_brand_admin
+UPDATE admin_users
+SET role = 'multi_brand_admin'
+WHERE role = 'brand_admin'
+  AND id IN (
+    SELECT admin_user_id FROM admin_user_brands
+    GROUP BY admin_user_id HAVING COUNT(*) > 1
+  );
+
+-- 5. New RPCs for adding/removing brand access
+CREATE OR REPLACE FUNCTION add_admin_user_brand(
+  p_admin_user_id UUID, p_brand_id UUID, p_added_by UUID
+) RETURNS void LANGUAGE sql SECURITY DEFINER AS $$
+  INSERT INTO admin_user_brands (admin_user_id, brand_id, added_by)
+  VALUES (p_admin_user_id, p_brand_id, p_added_by)
+  ON CONFLICT DO NOTHING;
+  UPDATE admin_users SET role = 'multi_brand_admin'
+  WHERE id = p_admin_user_id
+    AND role = 'brand_admin'
+    AND (SELECT COUNT(*) FROM admin_user_brands WHERE admin_user_id = p_admin_user_id) > 1;
+$$;
+
+CREATE OR REPLACE FUNCTION remove_admin_user_brand(
+  p_admin_user_id UUID, p_brand_id UUID
+) RETURNS void LANGUAGE sql SECURITY DEFINER AS $$
+  DELETE FROM admin_user_brands
+  WHERE admin_user_id = p_admin_user_id AND brand_id = p_brand_id;
+  UPDATE admin_users SET role = 'brand_admin'
+  WHERE id = p_admin_user_id
+    AND role = 'multi_brand_admin'
+    AND (SELECT COUNT(*) FROM admin_user_brands WHERE admin_user_id = p_admin_user_id) = 1;
+$$;
+```
+
+The `admin_users.brand_id` column is **kept** for backwards compat. A follow-up migration drops it after we verify nothing reads it.
+
+## Error Handling & Security Boundaries
+
+### Three failure modes
+
+1. **Requested brand not in `brand_ids`** (e.g., URL param has a brand the admin doesn't have):
+   - `getActiveBrandId()` returns `null`
+   - Server action returns `{ success: false, error: "Brand access required" }`
+   - Page renders `<AdminAccessDenied />` with: "You don't have access to that brand. [Switch to a brand you have access to]"
+
+2. **Cookie brand no longer in `brand_ids`** (admin's access was revoked while cookie was still set):
+   - `getActiveBrandId()` falls through to `adminUser.brand_id`, then first of `brand_ids`
+   - Silent recovery — no error, no UI flash
+   - The dropped brand just disappears from the dropdown next page load
+
+3. **Platform admin acting on a brand they don't own:**
+   - Platform admin: `brand_ids = ["*"]` (sentinel) — RPCs treat as "all brands"
+   - Server action: never blocks platform admin from any brand
+   - This is intentional — platform admin = superuser
+
+### Validation placement (defense in depth)
+
+- Server action: `getActiveBrandId(adminUser, requested)` validates.
+- Server action: `assertBrandAccess(adminUser, brandIdFromUrl)` validates (separate, for cases where the brandId comes from URL/form/RPC return rather than `getActiveBrandId`).
+- RPC: still trusts `p_brand_id` (SECURITY DEFINER) — application layer is the gate, matching the existing architecture.
+
+### Audit logging (additive)
+
+- `admin_user_brands.added_by` column tracks who added an admin to a brand.
+- Audit log entry on add/remove: out of scope for v1; documented for follow-up.
+
+## Testing
+
+### Unit tests (`vitest` — new dev dependency)
+
+- `src/lib/brand-scope.test.ts`:
+  - `resolveActiveBrandId(platformAdmin, "X")` → `"X"`
+  - `resolveActiveBrandId(brandAdmin, "X")` where X is their brand → `"X"`
+  - `resolveActiveBrandId(brandAdmin, "Y")` where Y is not their brand → `null`
+  - `getActiveBrandId(multiBrandAdmin)` with cookie set to valid brand → that brand
+  - `getActiveBrandId(multiBrandAdmin)` with cookie set to revoked brand → first of `brand_ids`
+  - `assertBrandAccess(...)` throws for non-platform-admin with invalid brand
+  - `setActiveBrand(null)` rejected for non-platform-admin
+  - `setActiveBrand("X")` rejected for admin without X in `brand_ids`
+
+### Integration tests (Playwright — already in repo)
+
+- `tests/admin/multi-brand.spec.ts`:
+  - As `multi_brand_admin`, dropdown shows 2+ brands
+  - Click brand B → URL stays, cookie updates, page data refreshes to brand B
+  - Direct-navigate to `/admin/orders?brand=<other-brand>` for a brand admin returns access denied
+  - As `platform_admin`, "All brands" option is present and works
+  - As `brand_admin` with 1 brand, no dropdown is shown
+
+### Migration smoke test (manual, documented in MEMORY.md)
+
+- Before migration: 5 brand_admins exist, each with 1 brand
+- After migration: 5 rows in `admin_user_brands`, all `role = 'brand_admin'`
+- Create a 6th admin with 2 brands via `add_admin_user_brand` → `role = 'multi_brand_admin'`, 2 rows in junction
+- Remove one of their brands via `remove_admin_user_brand` → `role` demotes to `brand_admin`, 1 row in junction
+
+## Out of Scope (v1)
+
+- Per-(admin, brand) permission overrides
+- Brand-group / parent-org concept
+- "Last accessed brand" auto-redirect
+- UI for managing `admin_user_brands` rows (Supabase Studio works for now)
+- Dropping the legacy `admin_users.brand_id` column (follow-up `220_*` migration)
+- Audit log entries for add/remove (junction's `added_by` column is the seed)
+
+## Implementation Order
+
+1. Migration `204_multi_brand_admin.sql` applied
+2. `src/lib/brand-scope.ts` + unit tests (TDD)
+3. `AdminUser` type updated; `getAdminUser()` returns `brand_ids`
+4. `setActiveBrand` server action + tests
+5. `listBrandsForAdmin` server function + tests
+6. BrandSelector UI component
+7. Wire BrandSelector into AdminHeader
+8. Server action migration (~30 actions) — mechanical one-line swap each
+9. Page server component migration (~10+ pages) — same pattern
+10. Playwright integration tests
+11. Manual smoke test of the migration on dev DB