Enforce tenant isolation in the data layer instead of per route

Every route had to remember to add the business filter to every query; nothing stopped one that forgot. The audit for this change found several that had: the M-Pesa status re-check, the stock ledger's duplicate checks, the daily-inventory and branch-price upserts, a cash-sale replay lookup, several load-by-id lookups, and every populate(). - tenantGuard: a Mongoose plugin on all ten business-scoped models. Any find/update/delete/count/distinct, or an aggregate whose first stage is not a $match, that does not pin exactly one businessId throws TenantScopeError before reaching the database ($in, $exists and other operators do not count). - crossTenant("reason", fn): the explicit, documented exemption for the queries that must span businesses - login's email lookup, refresh and invite-token lookups, the M-Pesa callback, the platform console and the maintenance scripts. git grep crossTenant lists them all. - scopedPopulate: populated branch, product and staff names are also restricted to the business. - Every flagged query site now names the business (or is exempted with a reason). - Tests: a check that every model with a businessId field carries the guard; the guard refusing unscoped queries of every kind; and a route sweep where business A sends business B's ids to every read route (nothing of B's comes back) and every write route (all refused, B's data unchanged). Test-side database inspections go through db(), an explicit test exemption. Removing one route's business filter makes the suite fail. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Merge remote-tracking branch 'origin/fix/per-business-identity' into fix/enforced-tenant-isolation
2026-10-12 11:52:35 +03:00 · 2026-10-12 11:40:38 +03:00 · 2026-10-12 11:31:45 +03:00
47 changed files with 849 additions and 124 deletions
@@ -13,8 +13,10 @@ JWT_REFRESH_TTL=30d
 DELIVERY_MAX_DEVICES=2

 # ---- Platform operator ----
-# Comma-separated emails with cross-tenant access to /platform. Create these
-# accounts with `npm run seed`; public signup refuses these addresses.
+# Comma-separated emails with cross-tenant access to /platform. The account
+# must also carry the platformAdmin flag, set only by `npm run seed` or
+# `npm run migrate:identity`. Removing an email here revokes access.
+# Public signup refuses these addresses.
 PLATFORM_ADMIN_EMAILS=

 # ---- Invite links ----
@@ -131,12 +131,57 @@ prices read-only.
  mismatch.
 - The Products page always shows default prices.

+## People in more than one business
+
+Email and phone are unique **within a business**, not across the platform,
+so one person can work for two businesses. Each account has its own
+password and role.
+
+- Login looks the email up in every business. If the password matches one
+  account, it signs straight in; if it matches several, the login page asks
+  which business. Someone with a wrong password learns nothing about which
+  businesses an email belongs to, and a wrong guess never resets the
+  failed-login count of another business's account.
+- Signup and staff creation only check for duplicates inside the business,
+  so they no longer reveal whether an email or phone is registered
+  elsewhere.
+- Platform-operator access now needs the `platformAdmin` flag on the
+  account as well as the email in `PLATFORM_ADMIN_EMAILS`. Without the
+  flag, any owner could create a staff account with the operator's email
+  in their own business. The flag is only set by `npm run seed` and
+  `npm run migrate:identity`, never through the app.
+
+**Deploying this change:** run `npm run migrate:identity` straight after
+the deploy. It flags the existing operator accounts and swaps the old
+platform-wide unique indexes for per-business ones. Until it runs,
+operators cannot open the Platform console and a second business cannot
+reuse an email. It is safe to re-run.
+
+## Tenant isolation is enforced
+
+Every model that holds one business's data carries a guard
+(`src/lib/server/tenantGuard.ts`). A query that does not name exactly one
+business (`businessId: <id>`) throws `TenantScopeError` before it reaches
+the database, so a route that forgets the business filter fails loudly in
+development and in the tests instead of reading or changing another
+business's data.
+
+- Guarded: User, Branch, Product, BranchPricing, Transaction,
+  DailyInventory, Expense, Purchase, StockMovement, StockTransfer. A test
+  fails if a new model with a `businessId` field is added without the guard.
+- Queries that genuinely span businesses must be wrapped in
+  `crossTenant("reason", ...)`: login's email lookup, refresh-session and
+  invite-token lookups, the M-Pesa callback, the platform console, and the
+  maintenance scripts. `git grep crossTenant` lists every one.
+- Related records are loaded with `scopedPopulate`, so a populated branch,
+  product or staff name is also restricted to the business.
+- `tests/isolation.test.ts` sweeps every read route with another business's
+  ids (nothing of theirs comes back) and every write route (all refused,
+  their data unchanged).
+- Not guarded, by design: Business (the tenant itself, always looked up by
+  the session's id), UserSession, MpesaCallbackLog and StockLock.
+
 ## Still open
- **Global email and phone uniqueness.** One person cannot work for two
-  businesses, and signup reveals whether an address is already registered.
- **Isolation by convention.** Tenant filters are still written per route.
-  The tests cover the sales, stock, transfer and access paths, not every
-  route.
 - **Cost of goods is an average.** It uses each product's average buying
  price across the business, not first-in-first-out per branch. Units sold
  with no purchase on record are counted and flagged, but have no cost.
@@ -11,7 +11,8 @@
    "migrate:multitenant": "tsx scripts/migrate-multitenant.ts",
    "test": "vitest run",
    "typecheck": "tsc --noEmit",
-    "backfill:stock": "tsx scripts/backfill-stock-from-purchases.ts"
+    "backfill:stock": "tsx scripts/backfill-stock-from-purchases.ts",
+    "migrate:identity": "tsx scripts/migrate-per-business-identity.ts"
  },
  "dependencies": {
    "axios": "^1.7.7",
@@ -13,6 +13,7 @@ import { Expense } from "../src/lib/server/models/Expense";
 import { Purchase } from "../src/lib/server/models/Purchase";
 import { Business } from "../src/lib/server/models/Business";
 import { DEFAULT_TIER, TRIAL_DAYS } from "../src/lib/tiers";
+import { crossTenant } from "../src/lib/server/tenantGuard";

 async function migrate() {
  await connectDb();
@@ -75,7 +76,7 @@ async function migrate() {
  process.exit(0);
 }

-migrate().catch((err) => {
+crossTenant("one-off migration of data from before businesses existed", migrate).catch((err) => {
  console.error("migration failed:", err.message);
  process.exit(1);
 });
@@ -0,0 +1,50 @@
+import dotenv from "dotenv";
+import path from "path";
+dotenv.config({ path: path.resolve(__dirname, "../.env.local") });
+
+import mongoose from "mongoose";
+import { connectDb } from "../src/lib/server/db";
+import { User } from "../src/lib/server/models/User";
+import { platformAdminEmails } from "../src/lib/server/platform";
+import { crossTenant } from "../src/lib/server/tenantGuard";
+
+/**
+ * One-off, safe to re-run. Moves user identity from platform-wide to
+ * per-business uniqueness:
+ *
+ *  1. Marks today's platform operators. Until now an operator was anyone
+ *     whose email was in PLATFORM_ADMIN_EMAILS; emails were unique, so
+ *     that was one account each. From now on emails are only unique per
+ *     business, so access also needs the platformAdmin flag on the account.
+ *     Run this BEFORE dropping the old index, while each listed email
+ *     still matches exactly one account.
+ *  2. Syncs the User indexes: drops the old unique `email_1` and
+ *     `phoneNumber_1`, creates unique (businessId, email) and
+ *     (businessId, phoneNumber), and a plain email lookup index.
+ *
+ *   npm run migrate:identity
+ */
+async function main() {
+  await connectDb();
+
+  for (const email of platformAdminEmails()) {
+    const accounts = await User.find({ email }).select("_id").lean();
+    if (accounts.length === 1) {
+      await User.updateOne({ _id: accounts[0]._id }, { $set: { platformAdmin: true } });
+      console.log(`Platform operator: ${email}`);
+    } else if (accounts.length === 0) {
+      console.warn(`No account for ${email} - create it with npm run seed.`);
+    } else {
+      console.warn(`${email} has ${accounts.length} accounts - set platformAdmin on the right one by hand.`);
+    }
+  }
+
+  const dropped = await User.syncIndexes();
+  console.log(`User indexes synced. Dropped: ${dropped.length ? dropped.join(", ") : "none"}.`);
+  await mongoose.disconnect();
+}
+
+crossTenant("identity migration spans every business", main).catch((err) => {
+  console.error("migration failed:", err.message);
+  process.exit(1);
+});
@@ -13,6 +13,8 @@ import { connectDb } from "../src/lib/server/db";
 import { User } from "../src/lib/server/models/User";
 import { Product } from "../src/lib/server/models/Product";
 import { Business } from "../src/lib/server/models/Business";
+import { isPlatformAdminEmail } from "../src/lib/server/platform";
+import { crossTenant } from "../src/lib/server/tenantGuard";

 /**
 * Run once against a fresh database: `npm run seed`.
@@ -39,10 +41,23 @@ async function seed() {
  }

  let business = await Business.findOne({ name: demoBusinessName });
-  const existing = await User.findOne({ email });
+  // Emails are unique per business, so look in the seeded business (or, for
+  // a legacy single-tenant database, for its one super admin).
+  const existing = business
+    ? await User.findOne({ email, businessId: business._id })
+    : await User.findOne({ email, role: "SUPER_ADMIN" });
+  // The seed is the only way (besides the identity migration) to make an
+  // operator: the flag is honoured only while the email is also listed in
+  // PLATFORM_ADMIN_EMAILS.
+  const platformAdmin = isPlatformAdminEmail(email);

  if (existing) {
    console.log(`Super admin (${email}) already exists, skipping`);
+    if (platformAdmin && !existing.platformAdmin) {
+      existing.platformAdmin = true;
+      await existing.save();
+      console.log(`Marked ${email} as a platform operator`);
+    }
    if (!business) {
      // Backfill a business for a legacy single-tenant admin if needed.
      business = await Business.create({ name: demoBusinessName, ownerId: existing._id });
@@ -61,6 +76,7 @@ async function seed() {
      phoneNumber: "254700000000",
      email,
      passwordHash,
+      platformAdmin,
      businessId: new mongoose.Types.ObjectId(), // temporary, overwritten below
    });
    business = await Business.create({ name: demoBusinessName, ownerId: owner._id });
@@ -92,7 +108,7 @@ async function seed() {
  process.exit(0);
 }

-seed().catch((err) => {
+crossTenant("seeding may find a legacy admin outside any business", seed).catch((err) => {
  console.error("seed failed:", err.message);
  process.exit(1);
 });
@@ -7,7 +7,9 @@ import { Branch } from "@/lib/server/models/Branch";
 import { Business } from "@/lib/server/models/Business";
 import { signAccessToken, generateRefreshToken, hashRefreshToken, refreshTtlMs } from "@/lib/server/jwt";
 import { ACCESS_COOKIE, REFRESH_COOKIE, accessCookieOptions, refreshCookieOptions } from "@/lib/server/auth";
-import { isPlatformAdminEmail } from "@/lib/server/platform";
+import { isPlatformAdmin } from "@/lib/server/platform";
+import { objectId } from "@/lib/server/validation";
+import { crossTenant } from "@/lib/server/tenantGuard";
 import { getEnv } from "@/lib/server/env";
 import { tenantAccessError } from "@/lib/server/subscription";

@@ -21,6 +23,9 @@ const loginSchema = z.object({
  password: z.string().min(1),
  deviceId: z.string().uuid(),
  deviceLabel: z.string().max(120).optional(),
+  // Which business to sign in to, when the same email and password match
+  // accounts in more than one (the first attempt returns the choices).
+  businessId: objectId.optional(),
 });

 async function enforceDeviceBinding(userId: string, deviceId: string) {
@@ -44,32 +49,72 @@ export async function POST(req: NextRequest) {
  if (!parsed.success) {
    return NextResponse.json({ error: parsed.error.issues[0]?.message ?? "Invalid request" }, { status: 400 });
  }
-  const { email, password, deviceId, deviceLabel } = parsed.data;
+  const { email, password, deviceId, deviceLabel, businessId } = parsed.data;

-  const user = await User.findOne({ email: email.toLowerCase() }).select("+passwordHash");
-  if (!user || !user.isActive) {
+  // An email is unique within a business, so it can belong to accounts in
+  // several businesses, each with its own password.
+  const filter: Record<string, unknown> = { email: email.toLowerCase(), isActive: true };
+  if (businessId) filter.businessId = businessId;
+  const candidates = await crossTenant("login looks an email up in every business", () =>
+    User.find(filter).select("+passwordHash").exec()
+  );
+  if (candidates.length === 0) {
    return NextResponse.json({ error: "Incorrect email or password" }, { status: 401 });
  }

-  if (user.lockedUntil && user.lockedUntil.getTime() > Date.now()) {
-    const minutesLeft = Math.ceil((user.lockedUntil.getTime() - Date.now()) / 60000);
+  const now = Date.now();
+  const unlocked = candidates.filter((u) => !u.lockedUntil || u.lockedUntil.getTime() <= now);
+  if (unlocked.length === 0) {
+    const soonest = Math.min(...candidates.map((u) => u.lockedUntil!.getTime()));
+    const minutesLeft = Math.ceil((soonest - now) / 60000);
    return NextResponse.json({ error: `Account locked. Try again in ${minutesLeft} minute(s).` }, { status: 423 });
  }

-  const validPassword = await user.comparePassword(password);
-  if (!validPassword) {
-    user.failedLoginAttempts += 1;
-    if (user.failedLoginAttempts >= MAX_FAILED_ATTEMPTS) {
-      user.lockedUntil = new Date(Date.now() + LOCKOUT_MS);
-      user.failedLoginAttempts = 0;
+  const matched = [];
+  for (const u of unlocked) {
+    if (await u.comparePassword(password)) matched.push(u);
+  }
+
+  if (matched.length === 0) {
+    // Count the failure against every account this email could have meant.
+    for (const u of unlocked) {
+      u.failedLoginAttempts += 1;
+      if (u.failedLoginAttempts >= MAX_FAILED_ATTEMPTS) {
+        u.lockedUntil = new Date(now + LOCKOUT_MS);
+        u.failedLoginAttempts = 0;
+      }
+      await u.save();
    }
-    await user.save();
    return NextResponse.json({ error: "Incorrect email or password" }, { status: 401 });
  }

-  user.failedLoginAttempts = 0;
-  user.lockedUntil = null;
-  await user.save();
+  // A correct password unlocks only the accounts it belongs to; a person
+  // with a different password in another business is not affected.
+  for (const u of matched) {
+    u.failedLoginAttempts = 0;
+    u.lockedUntil = null;
+    await u.save();
+  }
+
+  if (matched.length > 1) {
+    // Only someone who knows the password learns which businesses it opens.
+    const businesses = await Business.find({ _id: { $in: matched.map((u) => u.businessId) } })
+      .select("name")
+      .lean();
+    const nameById = new Map(businesses.map((b) => [b._id.toString(), b.name]));
+    return NextResponse.json(
+      {
+        error: "This email signs in to more than one business. Choose one.",
+        chooseBusiness: matched.map((u) => ({
+          businessId: u.businessId.toString(),
+          businessName: nameById.get(u.businessId.toString()) ?? "Business",
+          role: u.role,
+        })),
+      },
+      { status: 300 }
+    );
+  }
+  const user = matched[0];

  const tenantError = await tenantAccessError(user.businessId);
  if (tenantError) {
@@ -107,7 +152,7 @@ export async function POST(req: NextRequest) {
    deviceId,
  });

-  const branch = user.branchId ? await Branch.findById(user.branchId).lean() : null;
+  const branch = user.branchId ? await Branch.findOne({ _id: user.branchId, businessId: user.businessId }).lean() : null;
  const business = await Business.findById(user.businessId).lean();

  const res = NextResponse.json({
@@ -123,7 +168,7 @@ export async function POST(req: NextRequest) {
      email: user.email,
    },
    redirectTo: user.role === "DELIVERY" ? "/terminal" : "/admin/dashboard",
-    isPlatformAdmin: isPlatformAdminEmail(user.email),
+    isPlatformAdmin: isPlatformAdmin(user),
  });

  res.cookies.set(ACCESS_COOKIE, accessToken, accessCookieOptions());
@@ -4,7 +4,7 @@ import { User } from "@/lib/server/models/User";
 import { Branch } from "@/lib/server/models/Branch";
 import { Business } from "@/lib/server/models/Business";
 import { getAuth } from "@/lib/server/auth";
-import { isPlatformAdminEmail } from "@/lib/server/platform";
+import { isPlatformAdmin } from "@/lib/server/platform";
 import { isMpesaEnabled } from "@/lib/server/env";
 import { TIERS, effectiveMaxBranches, type TierId, type SubscriptionStatus } from "@/lib/tiers";

@@ -16,11 +16,11 @@ export async function GET(req: NextRequest) {
  const auth = getAuth(req);
  if (!auth) return NextResponse.json({ error: "Not authenticated" }, { status: 401 });

-  const user = await User.findById(auth.sub).lean();
+  const user = await User.findOne({ _id: auth.sub, businessId: auth.businessId }).lean();
  if (!user || !user.isActive) {
    return NextResponse.json({ error: "Not authenticated" }, { status: 401 });
  }
-  const branch = user.branchId ? await Branch.findById(user.branchId).lean() : null;
+  const branch = user.branchId ? await Branch.findOne({ _id: user.branchId, businessId: user.businessId }).lean() : null;
  const business = await Business.findById(user.businessId).lean();

  const tier = (business?.tier as TierId) ?? "STARTER";
@@ -38,7 +38,7 @@ export async function GET(req: NextRequest) {
      branchName: branch?.branchName ?? null,
      phoneNumber: user.phoneNumber,
      email: user.email,
-      isPlatformAdmin: isPlatformAdminEmail(user.email),
+      isPlatformAdmin: isPlatformAdmin(user),
    },
    subscription: {
      tier,
@@ -4,6 +4,7 @@ import { User } from "@/lib/server/models/User";
 import { UserSession } from "@/lib/server/models/UserSession";
 import { signAccessToken, generateRefreshToken, hashRefreshToken, refreshTtlMs } from "@/lib/server/jwt";
 import { tenantAccessError } from "@/lib/server/subscription";
+import { crossTenant } from "@/lib/server/tenantGuard";
 import { ACCESS_COOKIE, REFRESH_COOKIE, accessCookieOptions, refreshCookieOptions } from "@/lib/server/auth";

 export const runtime = "nodejs";
@@ -24,7 +25,9 @@ export async function POST(req: NextRequest) {
    return NextResponse.json({ error: "Session expired. Please log in again." }, { status: 401 });
  }

-  const user = await User.findById(session.userId);
+  const user = await crossTenant("a refresh session identifies its user before the business is known", () =>
+    User.findById(session.userId).exec()
+  );
  if (!user || !user.isActive) {
    await UserSession.deleteOne({ _id: session._id });
    return NextResponse.json({ error: "Account no longer active" }, { status: 401 });
@@ -53,22 +53,16 @@ export async function POST(req: NextRequest) {

  const lowerEmail = email.toLowerCase();

-  // Platform-operator rights are granted by email (PLATFORM_ADMIN_EMAILS)
-  // and signup does not verify email ownership, so an operator address
-  // must never be claimable through public signup. Operator accounts are
-  // created with `npm run seed` instead.
+  // Operator addresses are reserved, so nobody can open a business that
+  // looks like the operator's. (Access itself also needs the platformAdmin
+  // flag, which signup never sets.)
  if (isPlatformAdminEmail(lowerEmail)) {
    return NextResponse.json({ error: "This email cannot be used to sign up." }, { status: 403 });
  }

-  const emailTaken = await User.findOne({ email: lowerEmail }).lean();
-  if (emailTaken) {
-    return NextResponse.json({ error: "An account with this email already exists." }, { status: 409 });
-  }
-  const phoneTaken = await User.findOne({ phoneNumber: normalizedPhone }).lean();
-  if (phoneTaken) {
-    return NextResponse.json({ error: "An account with this phone number already exists." }, { status: 409 });
-  }
+  // No platform-wide duplicate check: a new business has no users yet, and
+  // the same person may already work for another business. (Checking would
+  // also tell anyone whether an email or phone is registered elsewhere.)

  const passwordHash = await bcrypt.hash(password, 12);

@@ -100,7 +94,7 @@ export async function POST(req: NextRequest) {
    await owner.save();
  } catch (e) {
    await Business.deleteOne({ _id: businessId }).catch(() => {});
-    await User.deleteOne({ _id: ownerId }).catch(() => {});
+    await User.deleteOne({ _id: ownerId, businessId }).catch(() => {});
    const msg = (e as Error).message || "";
    if (msg.includes("duplicate key")) {
      return NextResponse.json({ error: "An account with this email or phone already exists." }, { status: 409 });
@@ -106,7 +106,7 @@ export async function PUT(req: NextRequest) {
  }

  const row = await BranchPricing.findOneAndUpdate(
-    { branchId, productId },
+    { businessId: auth.businessId, branchId, productId },
    { businessId: auth.businessId, unitPrice, updatedBy: auth.sub },
    { upsert: true, new: true, setDefaultsOnInsert: true }
  ).lean();
@@ -71,14 +71,15 @@ export async function POST(req: NextRequest) {
    } catch (e) {
      return NextResponse.json({ error: (e as Error).message }, { status: 400 });
    }
+    // Unique within this business only (see the User model).
    const lowerEmail = manager.email.toLowerCase();
-    const emailTaken = await User.findOne({ email: lowerEmail }).lean();
+    const emailTaken = await User.exists({ businessId, email: lowerEmail });
    if (emailTaken) {
-      return NextResponse.json({ error: "An account with this email already exists." }, { status: 409 });
+      return NextResponse.json({ error: "Someone in your business already uses this email." }, { status: 409 });
    }
-    const phoneTaken = await User.findOne({ phoneNumber: managerPhone }).lean();
+    const phoneTaken = await User.exists({ businessId, phoneNumber: managerPhone });
    if (phoneTaken) {
-      return NextResponse.json({ error: "An account with this phone number already exists." }, { status: 409 });
+      return NextResponse.json({ error: "Someone in your business already uses this phone number." }, { status: 409 });
    }
  }

@@ -105,9 +106,9 @@ export async function POST(req: NextRequest) {
        { status: 201 }
      );
    } catch (err: any) {
-      await Branch.deleteOne({ _id: branch._id }).catch(() => {});
+      await Branch.deleteOne({ _id: branch._id, businessId }).catch(() => {});
      if (err?.code === 11000) {
-        return NextResponse.json({ error: "A user with this phone number or email already exists." }, { status: 409 });
+        return NextResponse.json({ error: "Someone in your business already uses this phone number or email." }, { status: 409 });
      }
      return NextResponse.json({ error: "Could not create the branch manager. Please try again." }, { status: 500 });
    }
@@ -5,6 +5,7 @@ import { Expense, EXPENSE_CATEGORIES } from "@/lib/server/models/Expense";
 import { Branch } from "@/lib/server/models/Branch";
 import { objectId } from "@/lib/server/validation";
 import { authorize, branchParam, MANAGERS } from "@/lib/server/auth";
+import { scopedPopulate } from "@/lib/server/tenantGuard";

 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
@@ -36,8 +37,8 @@ export async function GET(req: NextRequest) {
  }

  const expenses = await Expense.find(filter)
-    .populate("branchId", "branchName")
-    .populate("recordedBy", "name")
+    .populate(scopedPopulate("branchId", "branchName", auth.businessId))
+    .populate(scopedPopulate("recordedBy", "name", auth.businessId))
    .sort({ createdAt: -1 })
    .limit(500)
    .lean();
@@ -43,7 +43,7 @@ export async function POST(req: NextRequest) {

  const date = parsed.data.date ?? todayNairobi();
  const row = await DailyInventory.findOneAndUpdate(
-    { branchId, productId: parsed.data.productId, date },
+    { businessId: auth.businessId, branchId, productId: parsed.data.productId, date },
    { morningDispatched: parsed.data.morningDispatched, recordedBy: auth.sub, businessId: auth.businessId },
    { upsert: true, new: true, setDefaultsOnInsert: true }
  );
@@ -42,7 +42,7 @@ export async function POST(req: NextRequest) {

  const date = parsed.data.date ?? todayNairobi();
  const row = await DailyInventory.findOneAndUpdate(
-    { branchId, productId: parsed.data.productId, date },
+    { businessId: auth.businessId, branchId, productId: parsed.data.productId, date },
    { eveningPhysicalCount: parsed.data.eveningPhysicalCount, recordedBy: auth.sub, businessId: auth.businessId },
    { upsert: true, new: true, setDefaultsOnInsert: true }
  );
@@ -5,13 +5,16 @@ import { connectDb } from "@/lib/server/db";
 import { User } from "@/lib/server/models/User";
 import { Business } from "@/lib/server/models/Business";
 import { hashInviteToken } from "@/lib/server/invites";
+import { crossTenant } from "@/lib/server/tenantGuard";

 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";

 async function findInvitee(token: string) {
  if (!token || token.length > 100) return null;
-  const user = await User.findOne({ inviteTokenHash: hashInviteToken(token), isActive: true });
+  const user = await crossTenant("an invite token identifies its account before sign-in", () =>
+    User.findOne({ inviteTokenHash: hashInviteToken(token), isActive: true }).exec()
+  );
  if (!user || !user.inviteExpiresAt || user.inviteExpiresAt.getTime() < Date.now()) return null;
  return user;
 }
@@ -3,6 +3,7 @@ import { connectDb } from "@/lib/server/db";
 import { isMpesaEnabled } from "@/lib/server/env";
 import { Transaction } from "@/lib/server/models/Transaction";
 import { recordSaleMovement } from "@/lib/server/stock";
+import { crossTenant } from "@/lib/server/tenantGuard";
 import { MpesaCallbackLog } from "@/lib/server/models/MpesaCallbackLog";

 export const runtime = "nodejs";
@@ -69,7 +70,9 @@ export async function POST(req: NextRequest) {
    mpesaReceiptNumber = receiptItem ? String(receiptItem.Value) : null;
  }

-  const txn = await Transaction.findOne({ "mpesaDetails.checkoutRequestId": checkoutRequestId });
+  const txn = await crossTenant("the payment provider's callback is matched by checkout id", () =>
+    Transaction.findOne({ "mpesaDetails.checkoutRequestId": checkoutRequestId }).exec()
+  );

  if (!txn) {
    await MpesaCallbackLog.create({
@@ -26,7 +26,7 @@ export async function GET(req: NextRequest, { params }: { params: { transactionI
      const result = await queryStkStatus(txn.mpesaDetails.checkoutRequestId);
      const code = Number(result.ResultCode);
      if (!Number.isNaN(code) && code !== 1032) {
-        const fresh = await Transaction.findOne({ _id: txn._id, paymentStatus: "PENDING" });
+        const fresh = await Transaction.findOne({ _id: txn._id, businessId: auth.businessId, paymentStatus: "PENDING" });
        if (fresh) {
          fresh.paymentStatus = code === 0 ? "SUCCESS" : "FAILED";
          fresh.mpesaDetails.resultCode = code;
@@ -4,6 +4,7 @@ import { Business } from "@/lib/server/models/Business";
 import { User } from "@/lib/server/models/User";
 import { Branch } from "@/lib/server/models/Branch";
 import { requirePlatformAdmin } from "@/lib/server/platform";
+import { crossTenant } from "@/lib/server/tenantGuard";
 import { TIERS, effectiveMaxBranches, type TierId, type SubscriptionStatus } from "@/lib/tiers";

 export const runtime = "nodejs";
@@ -23,23 +24,26 @@ export async function GET(req: NextRequest) {
  const businesses = await Business.find({}).sort({ createdAt: -1 }).lean();

  // Usage counts per business in two grouped queries instead of N+1.
-  const [userCounts, branchCounts] = await Promise.all([
-    User.aggregate<{ _id: unknown; count: number }>([
-      { $group: { _id: "$businessId", count: { $sum: 1 } } },
-    ]),
-    Branch.aggregate<{ _id: unknown; count: number }>([
-      { $match: { isActive: { $ne: false } } },
-      { $group: { _id: "$businessId", count: { $sum: 1 } } },
-    ]),
-  ]);
+  const [userCounts, branchCounts] = await crossTenant("the platform console counts every business", () =>
+    Promise.all([
+      User.aggregate<{ _id: unknown; count: number }>([{ $group: { _id: "$businessId", count: { $sum: 1 } } }]).exec(),
+      Branch.aggregate<{ _id: unknown; count: number }>([
+        { $match: { isActive: { $ne: false } } },
+        { $group: { _id: "$businessId", count: { $sum: 1 } } },
+      ]).exec(),
+    ])
+  );
  const userMap = new Map(userCounts.map((u) => [String(u._id), u.count]));
  const branchMap = new Map(branchCounts.map((b) => [String(b._id), b.count]));

  // Owner contact lookup.
  const ownerIds = businesses.map((b) => b.ownerId);
-  const owners = await User.find({ _id: { $in: ownerIds } })
-    .select("name email phoneNumber")
-    .lean();
+  const owners = await crossTenant("the platform console lists every business's owner", () =>
+    User.find({ _id: { $in: ownerIds } })
+      .select("name email phoneNumber")
+      .lean()
+      .exec()
+  );
  const ownerMap = new Map(owners.map((o) => [String(o._id), o]));

  const rows = businesses.map((b) => {
@@ -7,6 +7,7 @@ import { ACTIVE_BRANCH, Branch } from "@/lib/server/models/Branch";
 import { objectId } from "@/lib/server/validation";
 import { recordMovement } from "@/lib/server/stock";
 import { authorize, branchParam, MANAGERS } from "@/lib/server/auth";
+import { scopedPopulate } from "@/lib/server/tenantGuard";

 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
@@ -36,8 +37,8 @@ export async function GET(req: NextRequest) {
  }

  const purchases = await Purchase.find(filter)
-    .populate("branchId", "branchName")
-    .populate("recordedBy", "name")
+    .populate(scopedPopulate("branchId", "branchName", auth.businessId))
+    .populate(scopedPopulate("recordedBy", "name", auth.businessId))
    .sort({ createdAt: -1 })
    .limit(500)
    .lean();
@@ -64,7 +64,7 @@ export async function POST(req: NextRequest) {
  const lockedBranch = branchId;
  try {
    const quantity = await withStockLock(auth.businessId, lockedBranch, data.productId, async () => {
-      const already = await StockMovement.exists({ type: "ADJUSTMENT", refId });
+      const already = await StockMovement.exists({ type: "ADJUSTMENT", refId, businessId: auth.businessId });
      if (!already) {
        const before = await stockOf(auth.businessId, lockedBranch, data.productId);
        const delta = data.mode === "COUNT" ? data.quantity - before : data.quantity;
@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { connectDb } from "@/lib/server/db";
 import { StockMovement } from "@/lib/server/models/StockMovement";
 import { authorize, branchParam, MANAGERS } from "@/lib/server/auth";
+import { scopedPopulate } from "@/lib/server/tenantGuard";

 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
@@ -23,9 +24,9 @@ export async function GET(req: NextRequest) {
  const movements = await StockMovement.find(filter)
    .sort({ createdAt: -1 })
    .limit(limit)
-    .populate("branchId", "branchName")
-    .populate("productId", "label unit")
-    .populate("recordedBy", "name")
+    .populate(scopedPopulate("branchId", "branchName", auth.businessId))
+    .populate(scopedPopulate("productId", "label unit", auth.businessId))
+    .populate(scopedPopulate("recordedBy", "name", auth.businessId))
    .lean();
  return NextResponse.json({ movements });
 }
@@ -5,6 +5,7 @@ import { ACTIVE_BRANCH, Branch } from "@/lib/server/models/Branch";
 import { Product } from "@/lib/server/models/Product";
 import { StockTransfer, IStockTransfer } from "@/lib/server/models/StockTransfer";
 import { authorize, branchParam, MANAGERS } from "@/lib/server/auth";
+import { scopedPopulate } from "@/lib/server/tenantGuard";
 import { objectId } from "@/lib/server/validation";
 import { recordMovement, stockOf, StockBusyError, withStockLock } from "@/lib/server/stock";

@@ -27,10 +28,10 @@ export async function GET(req: NextRequest) {
  const transfers = await StockTransfer.find(filter)
    .sort({ createdAt: -1 })
    .limit(100)
-    .populate("fromBranchId", "branchName")
-    .populate("toBranchId", "branchName")
-    .populate("productId", "label unit")
-    .populate("recordedBy", "name")
+    .populate(scopedPopulate("fromBranchId", "branchName", auth.businessId))
+    .populate(scopedPopulate("toBranchId", "branchName", auth.businessId))
+    .populate(scopedPopulate("productId", "label unit", auth.businessId))
+    .populate(scopedPopulate("recordedBy", "name", auth.businessId))
    .lean();
  return NextResponse.json({ transfers });
 }
@@ -167,10 +167,8 @@ export async function POST(req: NextRequest) {
      } catch (err: unknown) {
        if ((err as { code?: number })?.code !== 11000) throw err;
        // Already recorded by an earlier attempt: reuse it.
-        const existing = await Transaction.findOne({ clientUuid: `${sale.clientUuid}:${index}` });
-        if (!existing || existing.businessId.toString() !== auth.businessId) {
-          return reject("This sale id is already in use.");
-        }
+        const existing = await Transaction.findOne({ clientUuid: `${sale.clientUuid}:${index}`, businessId: auth.businessId });
+        if (!existing) return reject("This sale id is already in use.");
        txn = existing;
      }
      // Idempotent, and also repairs a line whose stock movement was not
@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { connectDb } from "@/lib/server/db";
 import { Transaction } from "@/lib/server/models/Transaction";
 import { authorize, branchParam } from "@/lib/server/auth";
+import { scopedPopulate } from "@/lib/server/tenantGuard";
 import { startOfTodayNairobi } from "@/lib/server/businessDay";

 export const runtime = "nodejs";
@@ -26,7 +27,7 @@ export async function GET(req: NextRequest) {
  const transactions = await Transaction.find(filter)
    .sort({ createdAt: -1 })
    .limit(limit)
-    .populate("branchId", "branchName")
+    .populate(scopedPopulate("branchId", "branchName", auth.businessId))
    .lean();

  return NextResponse.json({ transactions });
@@ -115,7 +115,7 @@ export async function POST(req: NextRequest) {
    return NextResponse.json({ user: obj, inviteUrl }, { status: 201 });
  } catch (err: any) {
    if (err?.code === 11000) {
-      return NextResponse.json({ error: "A user with this phone number or email already exists" }, { status: 409 });
+      return NextResponse.json({ error: "Someone in your business already uses this phone number or email" }, { status: 409 });
    }
    throw err;
  }
@@ -12,6 +12,18 @@ interface ActiveDevice {
  lastUsedAt: string;
 }

+interface BusinessChoice {
+  businessId: string;
+  businessName: string;
+  role: string;
+}
+
+const ROLE_LABELS: Record<string, string> = {
+  SUPER_ADMIN: "Owner",
+  BRANCH_MANAGER: "Branch manager",
+  DELIVERY: "Cashier",
+};
+
 export default function LoginPage() {
  const router = useRouter();
  const [email, setEmail] = useState("");
@@ -21,6 +33,8 @@ export default function LoginPage() {
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const [deviceConflict, setDeviceConflict] = useState<ActiveDevice[] | null>(null);
+  // Set when this email and password open accounts in more than one business.
+  const [choices, setChoices] = useState<BusinessChoice[] | null>(null);
  const [invited, setInvited] = useState(false);

  useEffect(() => {
@@ -29,6 +43,10 @@ export default function LoginPage() {

  async function handleSubmit(e: React.FormEvent) {
    e.preventDefault();
+    await signIn();
+  }
+
+  async function signIn(businessId?: string) {
    setError(null);
    setDeviceConflict(null);
    setLoading(true);
@@ -41,11 +59,15 @@ export default function LoginPage() {
          password,
          deviceId: getDeviceId(),
          deviceLabel: getDeviceLabel(),
+          businessId,
        }),
      });
      router.replace(result.redirectTo);
+      return;
    } catch (err) {
-      if (err instanceof ApiError && err.status === 409) {
+      if (err instanceof ApiError && err.status === 300) {
+        setChoices((err.body?.chooseBusiness as BusinessChoice[]) ?? []);
+      } else if (err instanceof ApiError && err.status === 409) {
        setDeviceConflict((err.body?.activeDevices as ActiveDevice[]) ?? []);
        setError(err.message);
      } else if (err instanceof ApiError) {
@@ -75,7 +97,35 @@ export default function LoginPage() {
            Run every branch with confidence — sales, stock, M-Pesa and cash.
          </p>

-          {deviceConflict ? (
+          {choices && !deviceConflict ? (
+            <div className="mt-8">
+              <p className="text-sm font-medium text-depth-800">Which business do you want to sign in to?</p>
+              {error && choices.length === 0 && <p className="mt-2 text-sm text-alert-600">{error}</p>}
+              <ul className="mt-3 space-y-2">
+                {choices.map((c) => (
+                  <li key={c.businessId}>
+                    <button
+                      onClick={() => signIn(c.businessId)}
+                      disabled={loading}
+                      className="tap-target flex w-full items-center justify-between rounded-xl2 border border-depth-200 bg-white px-4 text-left transition hover:border-flow-500 disabled:opacity-60"
+                    >
+                      <span className="font-medium text-depth-900">{c.businessName}</span>
+                      <span className="text-xs text-depth-500">{ROLE_LABELS[c.role] ?? c.role}</span>
+                    </button>
+                  </li>
+                ))}
+              </ul>
+              <button
+                onClick={() => {
+                  setChoices(null);
+                  setError(null);
+                }}
+                className="mt-4 text-sm text-depth-500 underline underline-offset-2"
+              >
+                Use a different email
+              </button>
+            </div>
+          ) : deviceConflict ? (
            <div className="mt-8 rounded-xl2 border border-alert-500/30 bg-alert-500/10 p-4">
              <p className="text-sm font-medium text-alert-600">{error}</p>
              <ul className="mt-3 space-y-2">
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 export interface IBranch extends Document {
@@ -30,5 +31,7 @@ const branchSchema = new Schema<IBranch>(
 /** Filter for branches that are in use. */
 export const ACTIVE_BRANCH = { isActive: { $ne: false } } as const;

+branchSchema.plugin(tenantGuard);
+
 export const Branch =
  (models.Branch as Model<IBranch>) || model<IBranch>("Branch", branchSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 export interface IDailyInventory extends Document {
@@ -40,6 +41,8 @@ dailyInventorySchema.index({ branchId: 1, date: 1 });
 // One ledger row per branch+product+day.
 dailyInventorySchema.index({ branchId: 1, productId: 1, date: 1 }, { unique: true });

+dailyInventorySchema.plugin(tenantGuard);
+
 export const DailyInventory =
  (models.DailyInventory as Model<IDailyInventory>) ||
  model<IDailyInventory>("DailyInventory", dailyInventorySchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 // Business expense categories. Kept as a constrained string set so the UI
@@ -46,5 +47,7 @@ expenseSchema.index({ category: 1 });

 // `models.Expense` guard avoids OverwriteModelError on serverless warm
 // re-invocations where the module is evaluated more than once.
+expenseSchema.plugin(tenantGuard);
+
 export const Expense =
  (models.Expense as Model<IExpense>) || model<IExpense>("Expense", expenseSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 export interface IProduct extends Document {
@@ -32,6 +33,8 @@ const productSchema = new Schema<IProduct>(
  { timestamps: true }
 );

+productSchema.plugin(tenantGuard);
+
 export const Product =
  (models.Product as Model<IProduct>) || model<IProduct>("Product", productSchema);

@@ -57,6 +60,8 @@ const branchPricingSchema = new Schema<IBranchPricing>(
 );
 branchPricingSchema.index({ branchId: 1, productId: 1 }, { unique: true });

+branchPricingSchema.plugin(tenantGuard);
+
 export const BranchPricing =
  (models.BranchPricing as Model<IBranchPricing>) ||
  model<IBranchPricing>("BranchPricing", branchPricingSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 // A recorded stock purchase from a supplier. Completing a purchase is what
@@ -40,5 +41,7 @@ const purchaseSchema = new Schema<IPurchase>(
 purchaseSchema.index({ branchId: 1, createdAt: -1 });
 purchaseSchema.index({ productId: 1 });

+purchaseSchema.plugin(tenantGuard);
+
 export const Purchase =
  (models.Purchase as Model<IPurchase>) || model<IPurchase>("Purchase", purchaseSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 export const MOVEMENT_TYPES = ["SALE", "PURCHASE", "TRANSFER_OUT", "TRANSFER_IN", "ADJUSTMENT"] as const;
@@ -46,6 +47,8 @@ stockMovementSchema.index({ type: 1, refId: 1 }, { unique: true });
 stockMovementSchema.index({ businessId: 1, branchId: 1, productId: 1 });
 stockMovementSchema.index({ businessId: 1, branchId: 1, createdAt: -1 });

+stockMovementSchema.plugin(tenantGuard);
+
 export const StockMovement =
  (models.StockMovement as Model<IStockMovement>) ||
  model<IStockMovement>("StockMovement", stockMovementSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 export interface IStockTransfer extends Document {
@@ -35,6 +36,8 @@ const stockTransferSchema = new Schema<IStockTransfer>(
 stockTransferSchema.index({ businessId: 1, clientUuid: 1 }, { unique: true });
 stockTransferSchema.index({ businessId: 1, createdAt: -1 });

+stockTransferSchema.plugin(tenantGuard);
+
 export const StockTransfer =
  (models.StockTransfer as Model<IStockTransfer>) ||
  model<IStockTransfer>("StockTransfer", stockTransferSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";

 export type PaymentMethod = "CASH" | "MPESA";
@@ -105,6 +106,8 @@ transactionSchema.index({ businessId: 1, createdAt: -1 });
 transactionSchema.index({ paymentStatus: 1 });
 transactionSchema.index({ businessId: 1, saleId: 1 });

+transactionSchema.plugin(tenantGuard);
+
 export const Transaction =
  (models.Transaction as Model<ITransaction>) ||
  model<ITransaction>("Transaction", transactionSchema);
@@ -1,3 +1,4 @@
+import { tenantGuard } from "@/lib/server/tenantGuard";
 import { Schema, model, models, Model, Types, Document } from "mongoose";
 import bcrypt from "bcryptjs";

@@ -10,8 +11,16 @@ export interface IUser extends Document {
  name: string;
  role: UserRole;
  branchId: Types.ObjectId | null; // null only valid for SUPER_ADMIN (business owner)
+  // Email and phone are unique WITHIN a business, not across the platform,
+  // so one person can work for two businesses (each account has its own
+  // password and role). Login asks which business when the same email and
+  // password match accounts in more than one.
  phoneNumber: string; // E.164-ish normalized Kenyan format — kept for contact/M-Pesa reference, not used for login
  email: string; // login identifier for every role, via the single /login page
+  // Platform operator (cross-tenant console). Only set by `npm run seed` or
+  // the identity migration, never through the app, and only honoured while
+  // the email is also listed in PLATFORM_ADMIN_EMAILS.
+  platformAdmin: boolean;
  passwordHash: string;
  isActive: boolean;
  failedLoginAttempts: number;
@@ -33,8 +42,9 @@ const userSchema = new Schema<IUser>(
    name: { type: String, required: true, trim: true },
    role: { type: String, enum: USER_ROLES, required: true, default: "DELIVERY" },
    branchId: { type: Schema.Types.ObjectId, ref: "Branch", default: null },
-    phoneNumber: { type: String, required: true, unique: true, index: true },
-    email: { type: String, required: true, unique: true, lowercase: true, trim: true },
+    phoneNumber: { type: String, required: true },
+    email: { type: String, required: true, lowercase: true, trim: true },
+    platformAdmin: { type: Boolean, default: false },
    passwordHash: { type: String, required: true, select: false },
    isActive: { type: Boolean, default: true },
    failedLoginAttempts: { type: Number, default: 0 },
@@ -45,6 +55,13 @@ const userSchema = new Schema<IUser>(
  { timestamps: true }
 );

+userSchema.index({ businessId: 1, email: 1 }, { unique: true });
+userSchema.index({ businessId: 1, phoneNumber: 1 }, { unique: true });
+// Login looks an email up across businesses. Named so it never clashes with
+// the old platform-wide unique `email_1` index, which the identity
+// migration (npm run migrate:identity) drops.
+userSchema.index({ email: 1 }, { name: "email_lookup" });
+
 // Enforce role/branch invariants at the model layer — belt-and-braces
 // alongside API-level validation. Every role authenticates the same way
 // now (email + password on the single /login page), so there is no
@@ -64,5 +81,7 @@ userSchema.methods.comparePassword = async function (password: string): Promise<
  return bcrypt.compare(password, this.passwordHash);
 };

+userSchema.plugin(tenantGuard);
+
 export const User =
  (models.User as Model<IUser>) || model<IUser>("User", userSchema);
@@ -26,21 +26,32 @@ import type { NextRequest } from "next/server";
 import { getAuth } from "@/lib/server/auth";
 import { User } from "@/lib/server/models/User";

+/**
+ * Whether this account is a platform operator. Two conditions, because
+ * emails are only unique within a business: any owner can create a staff
+ * account with any email in their own business, so an email match alone
+ * must never grant cross-tenant access. The account must also carry the
+ * platformAdmin flag, which the app never sets (seed/migration only).
+ * Removing an email from PLATFORM_ADMIN_EMAILS revokes access at once.
+ */
+export function isPlatformAdmin(user: { email?: string | null; platformAdmin?: boolean | null }): boolean {
+  return user.platformAdmin === true && isPlatformAdminEmail(user.email);
+}
+
 /**
 * Resolve and authorize the current request as a platform operator.
 * Returns the authenticated User's id/email on success, or null if the
 * caller is not a platform admin. The DB must already be connected.
- *
- * The JWT has no email, so we re-read the User and match its email
- * against PLATFORM_ADMIN_EMAILS.
 */
 export async function requirePlatformAdmin(
  req: NextRequest
 ): Promise<{ userId: string; email: string } | null> {
  const auth = getAuth(req);
  if (!auth) return null;
-  const user = await User.findById(auth.sub).select("email isActive").lean();
+  const user = await User.findOne({ _id: auth.sub, businessId: auth.businessId })
+    .select("email isActive platformAdmin")
+    .lean();
  if (!user || !user.isActive) return null;
-  if (!isPlatformAdminEmail(user.email)) return null;
+  if (!isPlatformAdmin(user)) return null;
  return { userId: auth.sub, email: user.email };
 }
@@ -4,6 +4,7 @@ import { ACTIVE_BRANCH, Branch } from "@/lib/server/models/Branch";
 import { Product } from "@/lib/server/models/Product";
 import { Purchase } from "@/lib/server/models/Purchase";
 import { StockLock } from "@/lib/server/models/StockLock";
+import { crossTenant } from "@/lib/server/tenantGuard";
 import type { ITransaction } from "@/lib/server/models/Transaction";

 type Id = Types.ObjectId | string;
@@ -26,7 +27,7 @@ export interface MovementInput {
 */
 export async function recordMovement(m: MovementInput): Promise<void> {
  await StockMovement.updateOne(
-    { type: m.type, refId: m.refId },
+    { type: m.type, refId: m.refId, businessId: m.businessId },
    {
      $setOnInsert: {
        businessId: m.businessId,
@@ -155,11 +156,14 @@ export async function getStockLevels(businessId: Id, branchId?: Id | null): Prom
 export async function backfillPurchaseMovements(businessId?: Id): Promise<number> {
  const filter: Record<string, unknown> = { productId: { $ne: null } };
  if (businessId) filter.businessId = new mongoose.Types.ObjectId(businessId.toString());
+  const purchases = businessId
+    ? await Purchase.find(filter).lean()
+    : await crossTenant("the backfill runs over every business", () => Purchase.find(filter).lean().exec());

  let added = 0;
-  for await (const p of Purchase.find(filter).lean().cursor()) {
+  for (const p of purchases) {
    const refId = p._id.toString();
-    if (await StockMovement.exists({ type: "PURCHASE", refId })) continue;
+    if (await StockMovement.exists({ type: "PURCHASE", refId, businessId: p.businessId })) continue;
    await recordMovement({
      businessId: p.businessId,
      branchId: p.branchId,
@@ -0,0 +1,114 @@
+import { AsyncLocalStorage } from "async_hooks";
+import { Types, type MongooseQueryMiddleware, type Schema } from "mongoose";
+
+/**
+ * Tenant isolation, enforced instead of remembered.
+ *
+ * Every model that holds one business's data is guarded: a query against
+ * it that does not name exactly one business (`businessId: <id>`) throws
+ * TenantScopeError before it reaches the database. A route that forgets
+ * the business filter therefore fails loudly in development and in the
+ * test suite, instead of quietly reading or changing another business's
+ * data in production.
+ *
+ * The few queries that legitimately span businesses (login looking an
+ * email up everywhere, an invite token, the payment provider's callback,
+ * the platform console, maintenance scripts) must say so explicitly:
+ *
+ *   await crossTenant("login looks the email up in every business", () => User.find(...));
+ *
+ * Guarded: find, findOne (and findById / exists), findOneAndUpdate /
+ * Delete / Replace, updateOne / updateMany, replaceOne, deleteOne /
+ * deleteMany, countDocuments, distinct, and aggregate (its first stage
+ * must be a $match naming the business). populate() runs a find on the
+ * referenced model, so populate through `scopedPopulate` below.
+ *
+ * Not guarded, by design: Business (the tenant itself, always looked up by
+ * the id from the session), UserSession (keyed by the signed-in user),
+ * MpesaCallbackLog (provider audit log), StockLock (key already contains
+ * the business). Document saves and inserts are covered by `businessId`
+ * being a required field.
+ */
+
+export class TenantScopeError extends Error {
+  constructor(model: string, op: string) {
+    super(
+      `Tenant isolation: ${model}.${op} must filter by a single businessId ` +
+        `(or run inside crossTenant("why", ...) if it really spans businesses).`
+    );
+    this.name = "TenantScopeError";
+  }
+}
+
+const crossTenantReason = new AsyncLocalStorage<string>();
+
+/**
+ * Run `fn`, whose queries deliberately span businesses. `reason` documents
+ * why. The result is awaited inside the scope, so a lazy Mongoose query
+ * returned by `fn` executes while the exemption applies.
+ */
+export function crossTenant<T>(reason: string, fn: () => PromiseLike<T>): Promise<T> {
+  if (!reason.trim()) throw new Error("crossTenant needs a reason");
+  return crossTenantReason.run(reason, async () => await fn());
+}
+
+/** True when the filter pins exactly one business. */
+export function namesOneBusiness(filter: unknown): boolean {
+  if (!filter || typeof filter !== "object") return false;
+  const f = filter as Record<string, unknown>;
+  const v = f.businessId;
+  if (typeof v === "string" || v instanceof Types.ObjectId) return true;
+  if (v && typeof v === "object" && "$eq" in (v as object)) {
+    const eq = (v as { $eq: unknown }).$eq;
+    return typeof eq === "string" || eq instanceof Types.ObjectId;
+  }
+  return Array.isArray(f.$and) && f.$and.some(namesOneBusiness);
+}
+
+const QUERY_OPS: MongooseQueryMiddleware[] = [
+  "find",
+  "findOne",
+  "findOneAndUpdate",
+  "findOneAndDelete",
+  "findOneAndReplace",
+  "updateOne",
+  "updateMany",
+  "replaceOne",
+  "deleteOne",
+  "deleteMany",
+  "countDocuments",
+  "distinct",
+];
+
+const guardedSchemas = new WeakSet<Schema>();
+
+/** Whether a schema has the guard (the test suite checks every business-scoped model does). */
+export function isTenantGuarded(schema: Schema): boolean {
+  return guardedSchemas.has(schema);
+}
+
+/** Mongoose plugin: apply to every schema with a `businessId` path. */
+export function tenantGuard(schema: Schema): void {
+  guardedSchemas.add(schema);
+
+  schema.pre(QUERY_OPS, function (this: any) {
+    if (crossTenantReason.getStore()) return;
+    if (!namesOneBusiness(this.getFilter())) throw new TenantScopeError(this.model.modelName, this.op);
+  });
+
+  schema.pre("aggregate", function (this: any) {
+    if (crossTenantReason.getStore()) return;
+    const first = this.pipeline()[0];
+    if (!first || !namesOneBusiness(first.$match)) {
+      throw new TenantScopeError(this._model?.modelName ?? "Model", "aggregate");
+    }
+  });
+}
+
+/**
+ * populate() options that keep the referenced documents inside the
+ * business too (populate queries the referenced model, which is guarded).
+ */
+export function scopedPopulate(path: string, select: string, businessId: string | Types.ObjectId) {
+  return { path, select, match: { businessId } };
+}
@@ -15,7 +15,7 @@ import * as login from "@/app/api/auth/login/route";
 import * as signup from "@/app/api/auth/signup/route";
 import * as stkpush from "@/app/api/mpesa/stkpush/route";
 import * as callback from "@/app/api/mpesa/callback/route";
-import { json, makeTenant, params, req, uuid } from "./helpers";
+import { json, makeTenant, params, req, uuid, db } from "./helpers";

 describe("role-based access on the backend", () => {
  it("blocks cashiers from owner-level money endpoints with 403", async () => {
@@ -78,7 +78,7 @@ describe("user deactivation", () => {
      params({ id: t.cashierA.id })
    );
    expect(res.status).toBe(200);
-    expect((await User.findById(t.cashierA.id))!.isActive).toBe(false);
+    expect((await db(() => User.findById(t.cashierA.id)))!.isActive).toBe(false);
    expect(await UserSession.countDocuments({ userId: t.cashierA.id })).toBe(0);
  });

@@ -105,7 +105,7 @@ describe("tenant status", () => {
  it("refuses login for a suspended business", async () => {
    const t = await makeTenant();
    const passwordHash = await bcrypt.hash("correct-horse", 4);
-    await User.updateOne({ _id: t.cashierA.id }, { passwordHash });
+    await db(() => User.updateOne({ _id: t.cashierA.id }, { passwordHash }));
    await Business.updateOne({ _id: t.businessId }, { subscriptionStatus: "SUSPENDED" });

    const res = await login.POST(
@@ -119,7 +119,7 @@ describe("tenant status", () => {
  it("still allows login for an active business", async () => {
    const t = await makeTenant();
    const passwordHash = await bcrypt.hash("correct-horse", 4);
-    await User.updateOne({ _id: t.managerA.id }, { passwordHash });
+    await db(() => User.updateOne({ _id: t.managerA.id }, { passwordHash }));
    const res = await login.POST(
      req("POST", "/api/auth/login", {
        body: { email: t.managerA.email, password: "correct-horse", deviceId: uuid() },
@@ -4,7 +4,7 @@ import { BranchPricing } from "@/lib/server/models/Product";
 import * as prices from "@/app/api/branch-prices/route";
 import * as products from "@/app/api/products/route";
 import * as cash from "@/app/api/transactions/cash/route";
-import { json, makeTenant, req, uuid, type Actor, type Tenant } from "./helpers";
+import { json, makeTenant, req, uuid, type Actor, type Tenant, db } from "./helpers";

 const setPrice = (as: Actor, branchId: string, productId: string, unitPrice: number) =>
  prices.PUT(req("PUT", "/api/branch-prices", { as, body: { branchId, productId, unitPrice } }));
@@ -44,7 +44,7 @@ describe("branch prices", () => {
    const t = await makeTenant();
    await setPrice(t.owner, t.branchA, t.water20, 180);
    await setPrice(t.owner, t.branchA, t.water20, 200);
-    expect(await BranchPricing.countDocuments({})).toBe(0);
+    expect(await db(() => BranchPricing.countDocuments({}))).toBe(0);

    await setPrice(t.owner, t.branchA, t.water5, 55);
    const reset = await prices.DELETE(
@@ -85,6 +85,6 @@ describe("branch prices", () => {
    expect((await setPrice(t.owner, other.branchA, t.water20, 150)).status).toBe(404);
    expect((await setPrice(t.owner, t.branchA, other.water20, 150)).status).toBe(404);
    expect((await prices.GET(req("GET", "/api/branch-prices?branchId=" + other.branchA, { as: t.owner }))).status).toBe(404);
-    expect(await BranchPricing.countDocuments({})).toBe(0);
+    expect(await db(() => BranchPricing.countDocuments({}))).toBe(0);
  });
 });
@@ -4,7 +4,7 @@ import { StockTransfer } from "@/lib/server/models/StockTransfer";
 import { StockLock } from "@/lib/server/models/StockLock";
 import * as adjustments from "@/app/api/stock/adjustments/route";
 import * as transfers from "@/app/api/stock/transfers/route";
-import { makeTenant, req, uuid, type Tenant } from "./helpers";
+import { makeTenant, req, uuid, type Tenant, db } from "./helpers";

 async function openingStock(t: Tenant, quantity: number) {
  await adjustments.POST(
@@ -35,7 +35,7 @@ describe("concurrent stock changes", () => {
    expect(statuses.filter((s) => s === 409)).toHaveLength(3);
    expect(await stockOf(t.businessId, t.branchA, t.water20)).toBe(2);
    expect(await stockOf(t.businessId, t.branchB, t.water20)).toBe(8);
-    expect(await StockTransfer.countDocuments({})).toBe(2);
+    expect(await db(() => StockTransfer.countDocuments({}))).toBe(2);
  });

  it("holds across repeated races, not just once", async () => {
@@ -19,7 +19,7 @@ import * as profit from "@/app/api/reports/profit/route";
 import * as cash from "@/app/api/transactions/cash/route";
 import * as adjustments from "@/app/api/stock/adjustments/route";
 import * as transfers from "@/app/api/stock/transfers/route";
-import { json, makeTenant, params, req, uuid, type Tenant } from "./helpers";
+import { json, makeTenant, params, req, uuid, type Tenant, db } from "./helpers";

 async function setPlan(t: Tenant, tier: string, subscriptionStatus: string) {
  await Business.updateOne({ _id: t.businessId }, { tier, subscriptionStatus });
@@ -39,7 +39,7 @@ describe("F-01 trial branch allowance", () => {
  it("counts only active branches, and a paid Starter plan allows one", async () => {
    const t = await makeTenant();
    await setPlan(t, "STARTER", "TRIALING");
-    await Branch.updateOne({ _id: t.branchB }, { isActive: false });
+    await db(() => Branch.updateOne({ _id: t.branchB }, { isActive: false }));
    expect((await branches.POST(req("POST", "/x", { as: t.owner, body: newBranch("C") }))).status).toBe(201);

    await setPlan(t, "STARTER", "ACTIVE");
@@ -70,7 +70,7 @@ describe("F-06 branch deactivation", () => {
    expect(withStaff.status).toBe(409);
    expect((await withStaff.json()).error).toMatch(/active staff/);

-    await User.updateOne({ _id: t.cashierB.id }, { isActive: false });
+    await db(() => User.updateOne({ _id: t.cashierB.id }, { isActive: false }));
    expect((await deactivate()).status).toBe(200);

    // Hidden from pickers, kept on the Branches page.
@@ -82,7 +82,7 @@ describe("F-06 branch deactivation", () => {

  it("will not reactivate a branch past the plan's limit", async () => {
    const t = await makeTenant();
-    await Branch.updateOne({ _id: t.branchB }, { isActive: false });
+    await db(() => Branch.updateOne({ _id: t.branchB }, { isActive: false }));
    await setPlan(t, "STARTER", "ACTIVE");
    const res = await branchById.PATCH(req("PATCH", "/x", { as: t.owner, body: { isActive: true } }), params({ id: t.branchB }));
    expect(res.status).toBe(403);
@@ -152,7 +152,7 @@ describe("F-04 / F-05 / CAT-12 catalogue", () => {
    await adjustments.POST(
      req("POST", "/x", { as: t.owner, body: { clientUuid: uuid(), branchId: t.branchA, productId: t.water5, mode: "DELTA", quantity: 7 } })
    );
-    await Product.updateOne({ _id: t.water5 }, { isActive: false });
+    await db(() => Product.updateOne({ _id: t.water5 }, { isActive: false }));

    const forManager = await json(await products.GET(req("GET", "/api/products?includeInactive=1", { as: t.managerA })));
    const forCashier = await json(await products.GET(req("GET", "/api/products?includeInactive=1", { as: t.cashierA })));
@@ -228,13 +228,13 @@ describe("STA-04 staff invites", () => {
    expect((await invites.GET(req("GET", "/x"), params({ token }))).status).toBe(404);
    expect((await invites.GET(req("GET", "/x"), params({ token: fresh }))).status).toBe(200);

-    await User.updateOne({ _id: new mongoose.Types.ObjectId(userId) }, { inviteExpiresAt: new Date(Date.now() - 1000) });
+    await db(() => User.updateOne({ _id: new mongoose.Types.ObjectId(userId) }, { inviteExpiresAt: new Date(Date.now() - 1000) }));
    expect((await invites.GET(req("GET", "/x"), params({ token: fresh }))).status).toBe(404);
  });

  it("does not let a manager re-invite another branch's staff", async () => {
    const t = await makeTenant();
-    await User.updateOne({ _id: t.cashierB.id }, { inviteExpiresAt: new Date(Date.now() + 60_000) });
+    await db(() => User.updateOne({ _id: t.cashierB.id }, { inviteExpiresAt: new Date(Date.now() + 60_000) }));
    const res = await reinvite.POST(req("POST", "/x", { as: t.managerA }), params({ id: t.cashierB.id }));
    expect(res.status).toBe(403);
  });
@@ -7,6 +7,7 @@ import { User, UserRole } from "@/lib/server/models/User";
 import { Product } from "@/lib/server/models/Product";
 import { signAccessToken } from "@/lib/server/jwt";
 import { ACCESS_COOKIE } from "@/lib/server/auth";
+import { crossTenant } from "@/lib/server/tenantGuard";

 let phoneSeq = 0;
 function nextPhone(): string {
@@ -131,3 +132,8 @@ export async function json<T = any>(res: Response): Promise<{ status: number; bo
 export function uuid(): string {
  return randomUUID();
 }
+
+/** Tests may inspect and arrange any business's data directly. */
+export function db<T>(fn: () => PromiseLike<T>): Promise<T> {
+  return crossTenant("test inspects the database directly", fn);
+}
@@ -0,0 +1,152 @@
+import { describe, expect, it } from "vitest";
+import bcrypt from "bcryptjs";
+import { User } from "@/lib/server/models/User";
+import * as users from "@/app/api/users/route";
+import * as login from "@/app/api/auth/login/route";
+import * as me from "@/app/api/auth/me/route";
+import * as platformBusinesses from "@/app/api/platform/businesses/route";
+import { ACCESS_COOKIE } from "@/lib/server/auth";
+import { json, makeTenant, req, uuid, type Actor, type Tenant, db } from "./helpers";
+
+const PERSON = { name: "Wanjiru", email: "wanjiru@aquaflow.test", phoneNumber: "0722000111" };
+const OPERATOR = "operator@aquaflow.test"; // listed in PLATFORM_ADMIN_EMAILS by tests/setup.ts
+
+async function hire(t: Tenant, as: Actor, person = PERSON) {
+  return users.POST(
+    req("POST", "/api/users", { as, body: { ...person, role: "DELIVERY", branchId: t.branchA, password: "password-123" } })
+  );
+}
+
+const signIn = (email: string, password: string, businessId?: string) =>
+  login.POST(req("POST", "/api/auth/login", { body: { email, password, deviceId: uuid(), businessId } }));
+
+async function setPassword(email: string, businessId: string, password: string) {
+  await User.updateOne({ email, businessId }, { passwordHash: await bcrypt.hash(password, 4) });
+}
+
+function accessCookie(res: Response): string {
+  const cookie = res.headers.get("set-cookie") ?? "";
+  return cookie.match(new RegExp(`${ACCESS_COOKIE}=([^;]+)`))![1];
+}
+
+describe("email and phone are unique per business", () => {
+  it("lets one person work for two businesses with the same email and phone", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    expect((await hire(a, a.owner)).status).toBe(201);
+    expect((await hire(b, b.owner)).status).toBe(201);
+    expect(await db(() => User.countDocuments({ email: PERSON.email }))).toBe(2);
+  });
+
+  it("still refuses a duplicate inside the same business", async () => {
+    const a = await makeTenant("Alpha");
+    await hire(a, a.owner);
+    const sameEmail = await hire(a, a.owner, { ...PERSON, phoneNumber: "0733000222" });
+    const samePhone = await hire(a, a.owner, { ...PERSON, email: "other@aquaflow.test" });
+    expect([sameEmail.status, samePhone.status]).toEqual([409, 409]);
+  });
+});
+
+describe("login when an email exists in several businesses", () => {
+  it("signs straight in when only one account's password matches", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    await hire(a, a.owner);
+    await hire(b, b.owner);
+    await setPassword(PERSON.email, a.businessId, "alpha-secret");
+    await setPassword(PERSON.email, b.businessId, "beta-secret");
+
+    const res = await json(await signIn(PERSON.email, "beta-secret"));
+    expect(res.status).toBe(200);
+    expect(res.body.user.businessId).toBe(b.businessId);
+  });
+
+  it("asks which business when the same password opens both, then signs in to the one chosen", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    await hire(a, a.owner);
+    await hire(b, b.owner);
+    await setPassword(PERSON.email, a.businessId, "same-secret");
+    await setPassword(PERSON.email, b.businessId, "same-secret");
+
+    const ask = await json(await signIn(PERSON.email, "same-secret"));
+    expect(ask.status).toBe(300);
+    expect(ask.body.chooseBusiness.map((c: any) => c.businessName).sort()).toEqual(["Alpha", "Beta"]);
+
+    const chosen = await json(await signIn(PERSON.email, "same-secret", a.businessId));
+    expect(chosen.status).toBe(200);
+    expect(chosen.body.user.businessId).toBe(a.businessId);
+  });
+
+  it("reveals nothing about other businesses to a wrong password", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    await hire(a, a.owner);
+    await hire(b, b.owner);
+    const res = await json(await signIn(PERSON.email, "wrong-password"));
+    expect(res.status).toBe(401);
+    expect(res.body.chooseBusiness).toBeUndefined();
+    expect(res.body.error).toBe("Incorrect email or password");
+  });
+
+  it("does not let a wrong guess at one business unlock or reset the other", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    await hire(a, a.owner);
+    await hire(b, b.owner);
+    await setPassword(PERSON.email, a.businessId, "alpha-secret");
+    await setPassword(PERSON.email, b.businessId, "beta-secret");
+    for (let i = 0; i < 2; i++) await signIn(PERSON.email, "wrong");
+    await signIn(PERSON.email, "alpha-secret"); // resets Alpha's counter only
+    const [alpha, beta] = await Promise.all([
+      User.findOne({ email: PERSON.email, businessId: a.businessId }),
+      User.findOne({ email: PERSON.email, businessId: b.businessId }),
+    ]);
+    expect([alpha!.failedLoginAttempts, beta!.failedLoginAttempts]).toEqual([0, 2]);
+  });
+});
+
+describe("platform operator access", () => {
+  it("is not granted by an email match alone: another business cannot mint an operator", async () => {
+    const mallory = await makeTenant("Mallory Water");
+    await hire(mallory, mallory.owner, { name: "Fake operator", email: OPERATOR, phoneNumber: "0744000333" });
+    await setPassword(OPERATOR, mallory.businessId, "i-am-the-operator");
+
+    const res = await signIn(OPERATOR, "i-am-the-operator");
+    expect(res.status).toBe(200);
+    expect((await res.clone().json()).isPlatformAdmin).toBe(false);
+
+    const consoleRes = await platformBusinesses.GET(
+      req("GET", "/api/platform/businesses", { cookies: { [ACCESS_COOKIE]: accessCookie(res) } })
+    );
+    expect(consoleRes.status).toBe(403);
+  });
+
+  it("is granted to the flagged account whose email is listed", async () => {
+    const home = await makeTenant("Operator Co");
+    await hire(home, home.owner, { name: "Operator", email: OPERATOR, phoneNumber: "0755000444" });
+    await User.updateOne({ email: OPERATOR, businessId: home.businessId }, { platformAdmin: true });
+    await setPassword(OPERATOR, home.businessId, "real-operator");
+
+    const res = await signIn(OPERATOR, "real-operator");
+    const cookies = { [ACCESS_COOKIE]: accessCookie(res) };
+    expect((await platformBusinesses.GET(req("GET", "/x", { cookies }))).status).toBe(200);
+    expect((await json(await me.GET(req("GET", "/x", { cookies })))).body.user.isPlatformAdmin).toBe(true);
+  });
+
+  it("is revoked by removing the email from PLATFORM_ADMIN_EMAILS, even with the flag", async () => {
+    const home = await makeTenant("Operator Co");
+    await hire(home, home.owner, { name: "Operator", email: OPERATOR, phoneNumber: "0755000444" });
+    await User.updateOne({ email: OPERATOR, businessId: home.businessId }, { platformAdmin: true });
+    await setPassword(OPERATOR, home.businessId, "real-operator");
+    const cookies = { [ACCESS_COOKIE]: accessCookie(await signIn(OPERATOR, "real-operator")) };
+
+    const listed = process.env.PLATFORM_ADMIN_EMAILS;
+    process.env.PLATFORM_ADMIN_EMAILS = "";
+    try {
+      expect((await platformBusinesses.GET(req("GET", "/x", { cookies }))).status).toBe(403);
+    } finally {
+      process.env.PLATFORM_ADMIN_EMAILS = listed;
+    }
+  });
+});
@@ -0,0 +1,172 @@
+import { describe, expect, it } from "vitest";
+import mongoose from "mongoose";
+import { readdirSync } from "fs";
+import path from "path";
+import { crossTenant, isTenantGuarded, TenantScopeError } from "@/lib/server/tenantGuard";
+import { User } from "@/lib/server/models/User";
+import { Transaction } from "@/lib/server/models/Transaction";
+import { Expense } from "@/lib/server/models/Expense";
+import { StockMovement } from "@/lib/server/models/StockMovement";
+import { stockOf } from "@/lib/server/stock";
+import * as cash from "@/app/api/transactions/cash/route";
+import * as transactions from "@/app/api/transactions/route";
+import * as expenses from "@/app/api/expenses/route";
+import * as purchases from "@/app/api/purchases/route";
+import * as stock from "@/app/api/stock/route";
+import * as movements from "@/app/api/stock/movements/route";
+import * as transfers from "@/app/api/stock/transfers/route";
+import * as adjustments from "@/app/api/stock/adjustments/route";
+import * as summary from "@/app/api/dashboard/summary/route";
+import * as reconciliation from "@/app/api/dashboard/reconciliation/route";
+import * as profit from "@/app/api/reports/profit/route";
+import * as users from "@/app/api/users/route";
+import * as userById from "@/app/api/users/[id]/route";
+import * as reinvite from "@/app/api/users/[id]/invite/route";
+import * as branchById from "@/app/api/branches/[id]/route";
+import * as productById from "@/app/api/products/[id]/route";
+import * as branchPrices from "@/app/api/branch-prices/route";
+import * as dispatch from "@/app/api/inventory/dispatch/route";
+import * as eveningCount from "@/app/api/inventory/evening-count/route";
+import { db, json, makeTenant, params, req, uuid, type Tenant } from "./helpers";
+
+// Models that hold one business's data but are deliberately unguarded (see tenantGuard.ts).
+const UNGUARDED = new Set(["Business", "UserSession", "MpesaCallbackLog", "StockLock"]);
+
+describe("the tenant guard", () => {
+  it("is on every model that stores a businessId", async () => {
+    // Load every model file so none can be skipped by accident.
+    const dir = path.resolve(__dirname, "../src/lib/server/models");
+    for (const file of readdirSync(dir)) await import(path.join(dir, file));
+
+    const scoped = Object.values(mongoose.models).filter((m) => m.schema.path("businessId") && !UNGUARDED.has(m.modelName));
+    expect(scoped.length).toBeGreaterThanOrEqual(10);
+    const unguarded = scoped.filter((m) => !isTenantGuarded(m.schema)).map((m) => m.modelName);
+    expect(unguarded).toEqual([]);
+  });
+
+  it("refuses queries that do not name exactly one business", async () => {
+    const t = await makeTenant();
+    const attempts: [string, () => PromiseLike<unknown>][] = [
+      ["find", () => Transaction.find({ branchId: t.branchA })],
+      ["findById", () => User.findById(t.cashierA.id)],
+      ["exists", () => StockMovement.exists({ type: "SALE" })],
+      ["updateMany", () => Expense.updateMany({}, { amount: 0 })],
+      ["deleteMany", () => Transaction.deleteMany({ paymentMethod: "CASH" })],
+      ["countDocuments", () => User.countDocuments({})],
+      ["$in over businesses", () => User.find({ businessId: { $in: [t.businessId, new mongoose.Types.ObjectId()] } })],
+      ["$exists", () => User.find({ businessId: { $exists: true } })],
+      ["aggregate without $match", () => Transaction.aggregate([{ $group: { _id: "$businessId" } }])],
+      ["aggregate matching later", () => Transaction.aggregate([{ $sort: { createdAt: -1 } }, { $match: { businessId: t.businessId } }])],
+      ["unscoped populate", () => Expense.find({ businessId: t.businessId }).populate("branchId")],
+    ];
+    await Expense.create({ businessId: t.businessId, branchId: t.branchA, category: "Rent", amount: 1, description: "x", recordedBy: t.owner.id });
+    for (const [label, run] of attempts) {
+      await expect(Promise.resolve().then(run), label).rejects.toBeInstanceOf(TenantScopeError);
+    }
+  });
+
+  it("allows scoped queries, and cross-business ones only with a stated reason", async () => {
+    const t = await makeTenant();
+    expect(await User.countDocuments({ businessId: t.businessId })).toBe(4);
+    expect(await User.countDocuments({ $and: [{ businessId: t.businessId }, { role: "DELIVERY" }] })).toBe(2);
+    expect(await crossTenant("test", () => User.countDocuments({}))).toBe(4);
+    expect(() => crossTenant(" ", () => User.countDocuments({}))).toThrow(/reason/);
+    // The exemption ends with the callback.
+    await expect(Promise.resolve().then(() => User.countDocuments({}))).rejects.toBeInstanceOf(TenantScopeError);
+  });
+});
+
+/** Give tenant B one of everything, so a leak into tenant A's view would show. */
+async function seedVictim(b: Tenant) {
+  await adjustments.POST(
+    req("POST", "/x", { as: b.owner, body: { clientUuid: uuid(), branchId: b.branchA, productId: b.water20, mode: "DELTA", quantity: 50 } })
+  );
+  await cash.POST(
+    req("POST", "/x", { as: b.cashierA, body: { sales: [{ clientUuid: uuid(), lines: [{ productId: b.water20, quantity: 3 }] }] } })
+  );
+  await expenses.POST(req("POST", "/x", { as: b.owner, body: { branchId: b.branchA, category: "Rent", amount: 7777, description: "B rent" } }));
+  await purchases.POST(
+    req("POST", "/x", { as: b.owner, body: { branchId: b.branchA, supplierName: "B supplier", productId: b.water20, quantity: 5, unitCost: 99 } })
+  );
+  await transfers.POST(
+    req("POST", "/x", { as: b.owner, body: { clientUuid: uuid(), fromBranchId: b.branchA, toBranchId: b.branchB, productId: b.water20, quantity: 2 } })
+  );
+}
+
+describe("route sweep: another business's ids get nothing", () => {
+  it("every read route returns none of business B's data to business A, whatever ids A sends", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    await seedVictim(b);
+
+    const reads: [string, Response][] = [];
+    const get = async (label: string, handler: (r: any) => Promise<Response>, url: string) =>
+      reads.push([label, await handler(req("GET", url, { as: a.owner }))]);
+    const q = "?branchId=" + b.branchA;
+    await get("transactions", transactions.GET, "/api/transactions" + q);
+    await get("expenses", expenses.GET, "/api/expenses" + q);
+    await get("purchases", purchases.GET, "/api/purchases" + q);
+    await get("stock", stock.GET, "/api/stock" + q);
+    await get("movements", movements.GET, "/api/stock/movements" + q);
+    await get("transfers", transfers.GET, "/api/stock/transfers" + q);
+    await get("summary", summary.GET, "/api/dashboard/summary" + q);
+    await get("reconciliation", reconciliation.GET, "/api/dashboard/reconciliation" + q);
+    await get("profit", profit.GET, "/api/reports/profit" + q);
+    await get("users", users.GET, "/api/users" + q);
+    await get("branch prices", branchPrices.GET, "/api/branch-prices" + q);
+
+    const bIds = [b.businessId, b.branchA, b.branchB, b.water20, b.owner.id, b.cashierA.id];
+    for (const [label, res] of reads) {
+      const text = await res.text();
+      for (const id of bIds) expect(text.includes(id), `${label} leaked ${id}`).toBe(false);
+      expect(text.includes("7777") || text.includes("B supplier"), `${label} leaked B's figures`).toBe(false);
+    }
+    // Totals A sees are A's own (zero), not B's sale.
+    const totals = JSON.parse(await (await summary.GET(req("GET", "/api/dashboard/summary" + q, { as: a.owner }))).text());
+    expect(totals.totals.cashTotal).toBe(0);
+  });
+
+  it("every write route refuses business B's ids and leaves B's data untouched", async () => {
+    const a = await makeTenant("Alpha");
+    const b = await makeTenant("Beta");
+    await seedVictim(b);
+    const before = {
+      stockA: await stockOf(b.businessId, b.branchA, b.water20),
+      cashier: await db(() => User.findById(b.cashierA.id).lean()),
+      sales: await Transaction.countDocuments({ businessId: b.businessId }),
+    };
+
+    const as = a.owner;
+    const writes: [string, Response][] = [
+      ["deactivate B's cashier", await userById.PATCH(req("PATCH", "/x", { as, body: { isActive: false } }), params({ id: b.cashierA.id }))],
+      ["move B's cashier", await userById.PATCH(req("PATCH", "/x", { as, body: { branchId: a.branchA } }), params({ id: b.cashierA.id }))],
+      ["re-invite B's cashier", await reinvite.POST(req("POST", "/x", { as }), params({ id: b.cashierA.id }))],
+      ["rename B's branch", await branchById.PATCH(req("PATCH", "/x", { as, body: { branchName: "Pwned" } }), params({ id: b.branchA }))],
+      ["reprice B's product", await productById.PATCH(req("PATCH", "/x", { as, body: { unitPrice: 1 } }), params({ id: b.water20 }))],
+      ["branch price on B", await branchPrices.PUT(req("PUT", "/x", { as, body: { branchId: b.branchA, productId: b.water20, unitPrice: 1 } }))],
+      ["adjust B's stock", await adjustments.POST(req("POST", "/x", { as, body: { clientUuid: uuid(), branchId: b.branchA, productId: b.water20, mode: "COUNT", quantity: 0 } }))],
+      ["transfer out of B", await transfers.POST(req("POST", "/x", { as, body: { clientUuid: uuid(), fromBranchId: b.branchA, toBranchId: a.branchA, productId: b.water20, quantity: 1 } }))],
+      ["transfer into B", await transfers.POST(req("POST", "/x", { as, body: { clientUuid: uuid(), fromBranchId: a.branchA, toBranchId: b.branchA, productId: a.water20, quantity: 1 } }))],
+      ["expense on B", await expenses.POST(req("POST", "/x", { as, body: { branchId: b.branchA, category: "Rent", amount: 1, description: "x" } }))],
+      ["purchase into B", await purchases.POST(req("POST", "/x", { as, body: { branchId: b.branchA, supplierName: "x", productId: b.water20, quantity: 1, unitCost: 1 } }))],
+      ["dispatch at B", await dispatch.POST(req("POST", "/x", { as, body: { branchId: b.branchA, productId: b.water20, morningDispatched: 1 } }))],
+      ["count at B", await eveningCount.POST(req("POST", "/x", { as, body: { branchId: b.branchA, productId: b.water20, eveningPhysicalCount: 1 } }))],
+      ["sale of B's product", await cash.POST(req("POST", "/x", { as: a.cashierA, body: { sales: [{ clientUuid: uuid(), lines: [{ productId: b.water20, quantity: 1 }] }] } }))],
+    ];
+    for (const [label, res] of writes) {
+      if (label.startsWith("sale")) {
+        expect((await json(res)).body.results[0].status, label).toBe("rejected");
+      } else {
+        expect(res.status, label).toBeGreaterThanOrEqual(400);
+      }
+    }
+
+    expect(await stockOf(b.businessId, b.branchA, b.water20)).toBe(before.stockA);
+    expect(await db(() => User.findById(b.cashierA.id).lean())).toMatchObject({
+      isActive: before.cashier!.isActive,
+      branchId: before.cashier!.branchId,
+    });
+    expect(await Transaction.countDocuments({ businessId: b.businessId })).toBe(before.sales);
+    expect(await Expense.countDocuments({ businessId: b.businessId })).toBe(1);
+  });
+});
@@ -4,7 +4,7 @@ import { Product, BranchPricing } from "@/lib/server/models/Product";
 import { stockOf } from "@/lib/server/stock";
 import * as cash from "@/app/api/transactions/cash/route";
 import type { SaleResult } from "@/lib/syncProtocol";
-import { json, makeTenant, req, uuid, type Actor, type Tenant } from "./helpers";
+import { json, makeTenant, req, uuid, type Actor, type Tenant, db } from "./helpers";

 function sale(t: Tenant, cashier: Actor, lines: { productId: string; quantity: number; unitPrice?: number }[], extra = {}) {
  return {
@@ -31,7 +31,7 @@ describe("offline sale sync", () => {
    const { status, body } = await post(t.cashierA, [s]);
    expect(status).toBe(200);
    expect(body.results).toEqual([{ clientUuid: s.clientUuid, status: "saved", amountTotal: 580, priceMismatch: false }]);
-    expect(await Transaction.countDocuments({ saleId: s.clientUuid })).toBe(2);
+    expect(await db(() => Transaction.countDocuments({ saleId: s.clientUuid }))).toBe(2);
    expect(await stockOf(t.businessId, t.branchA, t.water20)).toBe(-2);
    expect(await stockOf(t.businessId, t.branchA, t.water5)).toBe(-3);
  });
@@ -42,7 +42,7 @@ describe("offline sale sync", () => {
    await post(t.cashierA, [s]);
    const replay = await post(t.cashierA, [s]);
    expect(replay.body.results[0]).toMatchObject({ clientUuid: s.clientUuid, status: "duplicate" });
-    expect(await Transaction.countDocuments({ saleId: s.clientUuid })).toBe(1);
+    expect(await db(() => Transaction.countDocuments({ saleId: s.clientUuid }))).toBe(1);
    expect(await stockOf(t.businessId, t.branchA, t.water20)).toBe(-1);
  });

@@ -78,7 +78,7 @@ describe("offline sale sync", () => {
    const otherCashiersSale = sale(t, t.cashierB, [{ productId: t.water20, quantity: 1 }]);
    const { body } = await post(t.cashierA, [otherCashiersSale]);
    expect(body.results[0].status).toBe("rejected");
-    expect(await Transaction.countDocuments({})).toBe(0);
+    expect(await db(() => Transaction.countDocuments({}))).toBe(0);
  });

  it("keeps a sale at the branch where it happened after the cashier is moved", async () => {
@@ -86,7 +86,7 @@ describe("offline sale sync", () => {
    const s = sale(t, t.cashierA, [{ productId: t.water20, quantity: 1 }]); // recorded at branch A
    const moved = { ...t.cashierA, branchId: t.branchB };
    await post(moved, [s]);
-    const txn = await Transaction.findOne({ saleId: s.clientUuid });
+    const txn = await db(() => Transaction.findOne({ saleId: s.clientUuid }));
    expect(txn!.branchId.toString()).toBe(t.branchA);
  });

@@ -97,13 +97,13 @@ describe("offline sale sync", () => {
    const foreignBranch = sale(t, t.cashierA, [{ productId: t.water20, quantity: 1 }], { branchId: other.branchA });
    const { body } = await post(t.cashierA, [foreignProduct, foreignBranch]);
    expect(body.results.map((r) => r.status)).toEqual(["rejected", "rejected"]);
-    expect(await Transaction.countDocuments({})).toBe(0);
+    expect(await db(() => Transaction.countDocuments({}))).toBe(0);
  });

  it("uses the branch price, flags a price the device showed differently, and keeps deactivated products sellable", async () => {
    const t = await makeTenant();
    await BranchPricing.create({ businessId: t.businessId, branchId: t.branchA, productId: t.water20, unitPrice: 180 });
-    await Product.updateOne({ _id: t.water5 }, { isActive: false });
+    await db(() => Product.updateOne({ _id: t.water5 }, { isActive: false }));
    const s = sale(t, t.cashierA, [
      { productId: t.water20, quantity: 1, unitPrice: 200 }, // stale price on the device
      { productId: t.water5, quantity: 1, unitPrice: 60 },