feat(auth): block protected account deletion in auth endpoints

TODO.md

@@ -115,7 +115,7 @@ This file is the single source of truth for roadmap and delivery progress.
 - [ ] [P1] Media refinement for artworks (medium, dimensions, year, framing, availability)
 - [ ] [P1] Users management (invite, roles, status)
 - [ ] [P1] Disable/ban user function and enforcement in auth/session checks
-- [ ] [P1] Owner/support protection rules in user management actions (cannot delete/demote)
+- [~] [P1] Owner/support protection rules in user management actions (cannot delete/demote)
 - [ ] [P1] Commissions management (request intake, owner, due date, notes)
 - [ ] [P1] Kanban workflow for commissions (new, scoped, in-progress, review, done)
 - [ ] [P1] Header banner management (message, CTA, active window)
@@ -191,6 +191,7 @@ This file is the single source of truth for roadmap and delivery progress.
 - [2026-02-10] Linux Playwright runtime depends on host packages; browser setup may require `playwright install --with-deps`.
 - [2026-02-10] Next.js 16 deprecates `middleware.ts` convention in favor of `proxy.ts`; admin route guard now lives at `apps/admin/src/proxy.ts`.
 - [2026-02-10] `server-only` imports break Bun CLI scripts; shared auth bootstrap code used by scripts must avoid Next-only runtime markers.
+- [2026-02-10] Auth delete-account endpoints now block protected users (support + canonical owner); admin user-management delete/demote guards remain to be implemented.
 
 ## How We Use This File
 

apps/admin/src/app/api/auth/[...all]/route.ts

@@ -1,5 +1,7 @@
 import {
+  auth,
   authRouteHandlers,
+  canDeleteUserAccount,
   canUserSelfRegister,
   ensureSupportUserBootstrap,
   ensureUserUsername,
@@ -40,6 +42,51 @@ function buildJsonRequest(request: Request, body: Record<string, unknown>): Requ
   })
 }
 
+function isDeleteUserAuthPath(pathname: string): boolean {
+  const actionPrefix = "/api/auth/"
+  const actionIndex = pathname.indexOf(actionPrefix)
+
+  if (actionIndex === -1) {
+    return false
+  }
+
+  const actionPath = pathname.slice(actionIndex + actionPrefix.length)
+  return actionPath === "delete-user" || actionPath.startsWith("delete-user/")
+}
+
+async function guardProtectedAccountDeletion(request: Request): Promise<Response | null> {
+  const pathname = new URL(request.url).pathname
+
+  if (!isDeleteUserAuthPath(pathname)) {
+    return null
+  }
+
+  const session = await auth.api
+    .getSession({
+      headers: request.headers,
+    })
+    .catch(() => null)
+
+  const userId = session?.user?.id
+
+  if (!userId) {
+    return null
+  }
+
+  const allowed = await canDeleteUserAccount(userId)
+
+  if (allowed) {
+    return null
+  }
+
+  return jsonResponse(
+    {
+      message: "This account is protected and cannot be deleted.",
+    },
+    403,
+  )
+}
+
 async function handleSignInPost(request: Request): Promise<Response> {
   await ensureSupportUserBootstrap()
 
@@ -136,6 +183,13 @@ async function handleSignUpPost(request: Request): Promise<Response> {
 
 export async function GET(request: Request): Promise<Response> {
   await ensureSupportUserBootstrap()
+
+  const deletionGuardResponse = await guardProtectedAccountDeletion(request)
+
+  if (deletionGuardResponse) {
+    return deletionGuardResponse
+  }
+
   return authRouteHandlers.GET(request)
 }
 
@@ -151,20 +205,48 @@ export async function POST(request: Request): Promise<Response> {
   }
 
   await ensureSupportUserBootstrap()
+
+  const deletionGuardResponse = await guardProtectedAccountDeletion(request)
+
+  if (deletionGuardResponse) {
+    return deletionGuardResponse
+  }
+
   return authRouteHandlers.POST(request)
 }
 
 export async function PATCH(request: Request): Promise<Response> {
   await ensureSupportUserBootstrap()
+
+  const deletionGuardResponse = await guardProtectedAccountDeletion(request)
+
+  if (deletionGuardResponse) {
+    return deletionGuardResponse
+  }
+
   return authRouteHandlers.PATCH(request)
 }
 
 export async function PUT(request: Request): Promise<Response> {
   await ensureSupportUserBootstrap()
+
+  const deletionGuardResponse = await guardProtectedAccountDeletion(request)
+
+  if (deletionGuardResponse) {
+    return deletionGuardResponse
+  }
+
   return authRouteHandlers.PUT(request)
 }
 
 export async function DELETE(request: Request): Promise<Response> {
   await ensureSupportUserBootstrap()
+
+  const deletionGuardResponse = await guardProtectedAccountDeletion(request)
+
+  if (deletionGuardResponse) {
+    return deletionGuardResponse
+  }
+
   return authRouteHandlers.DELETE(request)
 }

apps/admin/src/lib/auth/server.ts

@@ -452,6 +452,34 @@ export async function enforceOwnerInvariant(): Promise<OwnerInvariantState> {
   })
 }
 
+export async function canDeleteUserAccount(userId: string): Promise<boolean> {
+  const user = await db.user.findUnique({
+    where: { id: userId },
+    select: { role: true, isProtected: true },
+  })
+
+  if (!user) {
+    return false
+  }
+
+  // Protected/system users (support + canonical owner) are never deletable
+  // through self-service endpoints.
+  if (user.isProtected) {
+    return false
+  }
+
+  if (user.role !== "owner") {
+    return true
+  }
+
+  // Defensive fallback for drifted data; normal flow should already keep one owner.
+  const ownerCount = await db.user.count({
+    where: { role: "owner" },
+  })
+
+  return ownerCount > 1
+}
+
 export async function promoteFirstRegisteredUserToOwner(userId: string): Promise<boolean> {
   const promoted = await db.$transaction(async (tx) => {
     const existingOwner = await tx.user.findFirst({

docs/product-engineering/auth-baseline.md

@@ -13,6 +13,7 @@ Implemented in MVP0:
 - Prisma auth models (`user`, `session`, `account`, `verification`)
 - First registration creates owner; subsequent registrations are disabled
 - Owner invariant reconciliation is enforced in auth bootstrap and owner promotion flow
+- Protected accounts (support + canonical owner) are blocked from delete-account auth endpoints
 
 ## Environment
 
@@ -39,5 +40,5 @@ Optional:
 - Support user bootstrap is available via `bun run auth:seed:support`.
 - Root `bun run db:seed` runs DB seed and support-user seed.
 - `CMS_ADMIN_SELF_REGISTRATION_ENABLED` is temporary until admin settings UI manages this policy.
-- Owner invariant checks for future user-management mutations remain tracked in `TODO.md`.
+- Owner/support checks for future admin user-management mutations remain tracked in `TODO.md`.
 - Email verification and forgot/reset password pipelines are tracked for MVP2.