feat: add budget folder schema and migration

src/export/json.test.ts

@@ -114,6 +114,57 @@ describe("validation", () => {
   });
 });
 
+describe("import rejects invalid folder graph", () => {
+  const folder = (id: string, parentId: string | null, order: number) => ({ id, name: id, parentId, order });
+  const parse = (data: Dataset) => parseDatasetJson(JSON.stringify(data));
+
+  test("valid nested tree parses", () => {
+    const data = populated();
+    data.folders = [folder("home", null, 0), folder("bills", "home", 0)];
+    data.posts[0]!.folderId = "bills";
+    expect(parse(data).posts[0]!.folderId).toBe("bills");
+  });
+
+  test("rejects duplicate folder IDs", () => {
+    const data = populated();
+    data.folders = [folder("same", null, 0), folder("same", null, 1)];
+    expect(() => parse(data)).toThrow(ImportValidationError);
+  });
+
+  test("rejects missing parent", () => {
+    const data = populated();
+    data.folders = [folder("child", "missing", 0)];
+    expect(() => parse(data)).toThrow(ImportValidationError);
+  });
+
+  test("rejects missing item folders", () => {
+    const data = populated();
+    data.posts[0]!.folderId = "missing";
+    expect(() => parse(data)).toThrow(ImportValidationError);
+    data.posts[0]!.folderId = null;
+    data.recurring.push({
+      id: "rent", name: "Rent", order: 3, folderId: "missing", archived: false,
+      amount: { amount: 100, currency: "DKK" }, startDate: "2026-01",
+      recurrence: { kind: "everyNMonths", n: 1 }, anchoring: "calendar",
+      splitMode: "percent", splits: [{ postId: data.posts[0]!.id, value: 100, absorbsRemainder: true }],
+    });
+    expect(() => parse(data)).toThrow(ImportValidationError);
+  });
+
+  test("rejects cycles", () => {
+    const data = populated();
+    data.folders = [folder("a", "b", 0), folder("b", "a", 0)];
+    expect(() => parse(data)).toThrow(ImportValidationError);
+  });
+
+  test("rejects duplicate sibling order across item kinds", () => {
+    const data = populated();
+    data.folders = [folder("bills", null, 0)];
+    data.posts[0]!.order = 0;
+    expect(() => parse(data)).toThrow(ImportValidationError);
+  });
+});
+
 test("describeDataset counts what an import would replace", () => {
   expect(describeDataset(populated())).toEqual({
     posts: 3,
@@ -286,7 +337,8 @@ describe("recurring cost validation", () => {
   const valid = {
     id: "r1",
     name: "Rent",
-    order: 0,
+    order: 3,
+    folderId: null,
     archived: false,
     amount: { amount: 8000, currency: "DKK" },
     startDate: "2026-01",
@@ -530,7 +582,7 @@ describe("Purchase.source validation", () => {
   test("a source with a malformed occurrence date is refused", () => {
     const data: any = JSON.parse(withSource({ recurringId: "r1", occurrenceDate: "nope" }));
     data.recurring = [{
-      id: "r1", name: "Rent", order: 0, archived: false,
+      id: "r1", name: "Rent", order: 3, folderId: null, archived: false,
       amount: { amount: 8000, currency: "DKK" },
       startDate: "2026-01",
       recurrence: { kind: "everyNMonths", n: 1 },