fix: keep unassigned purchases visible in budget

src/ui/components/BudgetTree.test.tsx

@@ -6,7 +6,7 @@ import { act } from "react";
 import { createRoot } from "react-dom/client";
 import { MemoryRouter } from "react-router";
 import { createSeedDataset } from "../../domain/seed.ts";
-import { addBudgetFolder, addRecurringCost, confirmOccurrence, placeRecurringUnderPost } from "../../store/actions.ts";
+import { addBudgetFolder, addPurchase, addRecurringCost, confirmOccurrence, placeRecurringUnderPost } from "../../store/actions.ts";
 import { monthView } from "../../domain/views.ts";
 import { store } from "../../store/index.ts";
 import { PostTableLegend } from "./PostTable.tsx";
@@ -81,3 +81,24 @@ test("bills beneath a post are hidden until its post is expanded", () => {
     act(() => root.unmount()); container.remove(); Object.assign(store, original);
   }
 });
+
+test("Unassigned is a permanent Budget section with a create-post action", () => {
+  const data = createSeedDataset("2026-09");
+  const purchase = addPurchase(data, { date: "2026-09", description: "Train ticket", total: { amount: 50, currency: "DKK" }, splitMode: "percent", splits: [], schedule: null });
+  const original = { get: store.get, subscribe: store.subscribe };
+  store.get = () => data;
+  store.subscribe = () => () => {};
+  const container = document.createElement("div"); document.body.append(container);
+  const root = createRoot(container);
+  try {
+    act(() => root.render(<MemoryRouter><BudgetTree monthId="2026-09" rows={monthView(data, "2026-09").rows} /></MemoryRouter>));
+    for (const scope of [container.querySelector("table")!, container.querySelector("ul")!]) {
+      expect(scope.textContent).toContain("Unassigned");
+      const row = scope.querySelector(`[data-budget-item="${purchase.id}"]`)!;
+      expect(row.textContent).toContain("Train ticket");
+      expect(row.querySelector("button[aria-label='Create post for Train ticket']")).not.toBeNull();
+    }
+  } finally {
+    act(() => root.unmount()); container.remove(); Object.assign(store, original);
+  }
+});