Address the 11 October test report findings

The initial test report (run before the pilot-readiness changes) raised
seven findings and a retest plan. This closes the ones still open.

- F-01: a business on its free trial may run 2 active branches whatever
  its tier, so an owner can try transfers and per-branch stock. Only
  active branches count towards any limit.
- F-06: owners can rename branches and deactivate/reactivate them from
  the Branches page. A branch can only be deactivated once it holds no
  stock and no active staff; its history stays in every report, and it
  leaves every picker.
- F-04: the Products page lists deactivated products under a toggle with
  Reactivate. Deactivating warns about stock still on hand, which stays
  on the Stock page so it can be transferred or counted out.
- F-05: products carry a unit (L, ml, kg, g, pcs, tray, pack) instead of
  everything being litres.
- CAT-12: product prices must be above zero and names are unique per
  business, ignoring case.
- F-03: a reversed report period is refused by the page and the API, and
  the page labels which period the cards show. Report dates are Nairobi
  business days.
- F-07: cost of goods sold is units sold x average buying price. Stock
  bought in the period is reported separately, with a cash surplus line,
  so unsold stock no longer shows as a loss.
- STA-04: staff and new branch managers can be invited with a one-time,
  7-day link; the person sets their own password. Managers can issue a
  new link for their own cashiers.
- OFF-02 / POS-02: the till shows each product's stock and deducts every
  sale immediately, online or offline; it warns before selling more than
  the recorded stock, and has a Clear sale button.
- npm run backfill:stock turns purchases recorded before the stock ledger
  into stock, so existing tenants (and the report's ZERRO fixtures) start
  from what they bought.

tests/retest-plan.test.ts runs the report's completion and retest plan
and checks every balance and total it predicts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/api/branches/[id]/route.ts

@@ -3,7 +3,10 @@ import { z } from "zod";
 import { isValidObjectId } from "mongoose";
 import { connectDb } from "@/lib/server/db";
 import { Branch } from "@/lib/server/models/Branch";
+import { User } from "@/lib/server/models/User";
 import { authorize } from "@/lib/server/auth";
+import { branchLimitError } from "@/lib/server/subscription";
+import { getStockLevels } from "@/lib/server/stock";
 
 export const runtime = "nodejs";
 
@@ -11,10 +14,21 @@ const updateSchema = z
   .object({
     branchName: z.string().trim().min(1).max(120).optional(),
     locationCity: z.string().trim().min(1).max(120).optional(),
+    isActive: z.boolean().optional(),
   })
   .refine((v) => Object.keys(v).length > 0, { message: "No fields to update" });
 
-// PATCH /api/branches/:id — owner renames a branch or changes its city.
+/**
+ * PATCH /api/branches/:id — owner renames a branch, or deactivates /
+ * reactivates it. This is how an owner "removes" a branch: nothing is
+ * deleted, so its sales, purchases and stock history stay in every report.
+ *
+ * A branch can only be deactivated once it is empty, so nothing is left
+ * stranded in it:
+ *   - no stock on hand (transfer it out or count it to zero first), and
+ *   - no active staff (move or deactivate them first).
+ * Reactivating counts against the plan's branch limit again.
+ */
 export async function PATCH(req: NextRequest, { params }: { params: { id: string } }) {
   await connectDb();
   const gate = authorize(req, ["SUPER_ADMIN"]);
@@ -28,10 +42,36 @@ export async function PATCH(req: NextRequest, { params }: { params: { id: string
   if (!parsed.success) {
     return NextResponse.json({ error: parsed.error.issues[0]?.message ?? "Invalid request" }, { status: 400 });
   }
+  const { isActive, ...details } = parsed.data;
 
-  const branch = await Branch.findOneAndUpdate({ _id: params.id, businessId: auth.businessId }, parsed.data, {
-    new: true,
-  }).lean();
+  const branch = await Branch.findOne({ _id: params.id, businessId: auth.businessId });
   if (!branch) return NextResponse.json({ error: "Branch not found" }, { status: 404 });
+  const wasActive = branch.isActive !== false;
+
+  if (isActive === false && wasActive) {
+    const stock = (await getStockLevels(auth.businessId, branch._id)).filter((l) => l.quantity !== 0);
+    if (stock.length > 0) {
+      const list = stock.map((l) => `${l.quantity} x ${l.productLabel}`).join(", ");
+      return NextResponse.json(
+        { error: `Move or count out this branch's stock first (${list}).`, stock },
+        { status: 409 }
+      );
+    }
+    const staff = await User.countDocuments({ businessId: auth.businessId, branchId: branch._id, isActive: true });
+    if (staff > 0) {
+      return NextResponse.json(
+        { error: `${staff} active staff member(s) still work at this branch. Move or deactivate them first.` },
+        { status: 409 }
+      );
+    }
+  }
+  if (isActive === true && !wasActive) {
+    const limitError = await branchLimitError(auth.businessId);
+    if (limitError) return NextResponse.json({ error: limitError }, { status: 403 });
+  }
+
+  Object.assign(branch, details);
+  if (isActive !== undefined) branch.isActive = isActive;
+  await branch.save();
   return NextResponse.json({ branch });
 }