feat(auth): enforce single-owner invariant in bootstrap flow

TODO.md

@@ -26,7 +26,7 @@ This file is the single source of truth for roadmap and delivery progress.
 - [ ] [P1] Locale persistence and switcher base component (cookie/header + UI)
 - [x] [P1] Integrate Better Auth core configuration and session wiring
 - [x] [P1] Bootstrap first-run owner account creation via initial registration flow
-- [ ] [P1] Enforce invariant: exactly one owner user must always exist
+- [x] [P1] Enforce invariant: exactly one owner user must always exist
 - [x] [P1] Create hidden technical support user by default (non-demotable, non-deletable)
 - [~] [P1] Admin registration policy control (allow/deny self-registration for admin panel)
 - [x] [P1] First-start onboarding route for initial owner creation (`/welcome`)

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

@@ -359,7 +359,10 @@ export async function ensureSupportUserBootstrap(): Promise<void> {
     return
   }
 
-  supportBootstrapPromise = bootstrapSystemUsers()
+  supportBootstrapPromise = (async () => {
+    await bootstrapSystemUsers()
+    await enforceOwnerInvariant()
+  })()
 
   try {
     await supportBootstrapPromise
@@ -369,8 +372,88 @@ export async function ensureSupportUserBootstrap(): Promise<void> {
   }
 }
 
-export async function promoteFirstRegisteredUserToOwner(userId: string): Promise<boolean> {
+type OwnerInvariantState = {
+  ownerId: string | null
+  ownerCount: number
+  repaired: boolean
+}
+
+export async function enforceOwnerInvariant(): Promise<OwnerInvariantState> {
   return db.$transaction(async (tx) => {
+    const owners = await tx.user.findMany({
+      where: { role: "owner" },
+      orderBy: [{ createdAt: "asc" }, { id: "asc" }],
+      select: { id: true, isProtected: true, isBanned: true },
+    })
+
+    if (owners.length === 0) {
+      const candidate = await tx.user.findFirst({
+        where: {
+          role: {
+            not: "support",
+          },
+        },
+        orderBy: [{ createdAt: "asc" }, { id: "asc" }],
+        select: { id: true },
+      })
+
+      if (!candidate) {
+        return {
+          ownerId: null,
+          ownerCount: 0,
+          repaired: false,
+        }
+      }
+
+      await tx.user.update({
+        where: { id: candidate.id },
+        data: {
+          role: "owner",
+          isProtected: true,
+          isBanned: false,
+        },
+      })
+
+      return {
+        ownerId: candidate.id,
+        ownerCount: 1,
+        repaired: true,
+      }
+    }
+
+    const canonicalOwner = owners[0]
+    const extraOwnerIds = owners.slice(1).map((owner) => owner.id)
+
+    if (extraOwnerIds.length > 0) {
+      await tx.user.updateMany({
+        where: { id: { in: extraOwnerIds } },
+        data: {
+          role: "admin",
+          isProtected: false,
+        },
+      })
+    }
+
+    if (!canonicalOwner.isProtected || canonicalOwner.isBanned) {
+      await tx.user.update({
+        where: { id: canonicalOwner.id },
+        data: {
+          isProtected: true,
+          isBanned: false,
+        },
+      })
+    }
+
+    return {
+      ownerId: canonicalOwner.id,
+      ownerCount: 1,
+      repaired: extraOwnerIds.length > 0 || !canonicalOwner.isProtected || canonicalOwner.isBanned,
+    }
+  })
+}
+
+export async function promoteFirstRegisteredUserToOwner(userId: string): Promise<boolean> {
+  const promoted = await db.$transaction(async (tx) => {
     const existingOwner = await tx.user.findFirst({
       where: { role: "owner" },
       select: { id: true },
@@ -393,6 +476,12 @@ export async function promoteFirstRegisteredUserToOwner(userId: string): Promise
 
     return true
   })
+
+  if (promoted) {
+    await enforceOwnerInvariant()
+  }
+
+  return promoted
 }
 
 export function resolveRoleFromAuthSession(session: AuthSession | null | undefined): Role | null {

docs/product-engineering/auth-baseline.md

@@ -12,6 +12,7 @@ Implemented in MVP0:
 - Support fallback sign-in page: `/support/<CMS_SUPPORT_LOGIN_KEY>`
 - 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
 
 ## Environment
 
@@ -38,5 +39,5 @@ 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 hardening for all future user-management mutations remains tracked in `TODO.md`.
+- Owner invariant checks for future user-management mutations remain tracked in `TODO.md`.
 - Email verification and forgot/reset password pipelines are tracked for MVP2.