实现报销材料连续预览（07-27-yang-jun-reimbursement-readiness）

server/tests/unit/services/reimbursementMaterialPreview.test.js

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+const {
+  MaterialPreviewError,
+  createReimbursementMaterialPreviewStore,
+} = require("../../../src/services/reimbursementMaterialPreview");
+
+describe("reimbursement material preview store", () => {
+  it("keeps material and PDF page order in a bounded short-lived bundle", async () => {
+    let currentTime = 1_000;
+    const store = createReimbursementMaterialPreviewStore({
+      now: () => currentTime,
+      randomUUID: () => "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa",
+      rasterizePdf: vi.fn().mockResolvedValue([Buffer.from("pdf-page-1"), Buffer.from("pdf-page-2")]),
+      normalizeImage: vi.fn().mockResolvedValue(Buffer.from("image-page")),
+    });
+
+    const created = await store.createBundle({
+      actorId: "actor-1",
+      reimbursementId: "reimbursement-1",
+      expiresAt: 2_000,
+      materials: [
+        { id: "invoice-1", materialType: "invoice", materialIndex: 1, mimeType: "application/pdf", fileSize: 10 },
+        { id: "attachment-1", materialType: "attachment", materialIndex: 1, mimeType: "image/png", fileSize: 10 },
+      ],
+      readSource: async (material) => Buffer.from(material.id),
+    });
+
+    expect(created.bundle.pages.map((page) => [page.materialType, page.materialIndex, page.pageNumber])).toEqual([
+      ["invoice", 1, 1],
+      ["invoice", 1, 2],
+      ["attachment", 1, 1],
+    ]);
+    expect(store.getPage({ bundleId: created.bundleId, pageIndex: 1 })?.page.buffer.toString()).toBe("pdf-page-2");
+
+    currentTime = 2_001;
+    expect(store.getPage({ bundleId: created.bundleId, pageIndex: 0 })).toBeNull();
+  });
+
+  it("rejects source and page limits without keeping a partial bundle", async () => {
+    const store = createReimbursementMaterialPreviewStore({
+      limits: { maxMaterials: 1, maxSourceBytes: 10, maxPages: 1 },
+      rasterizePdf: vi.fn().mockResolvedValue([Buffer.from("one"), Buffer.from("two")]),
+    });
+
+    await expect(store.createBundle({
+      actorId: "actor-1",
+      reimbursementId: "reimbursement-1",
+      expiresAt: Date.now() + 1_000,
+      materials: [
+        { id: "one", materialType: "invoice", materialIndex: 1, mimeType: "application/pdf", fileSize: 6 },
+        { id: "two", materialType: "attachment", materialIndex: 1, mimeType: "image/png", fileSize: 6 },
+      ],
+      readSource: async () => Buffer.from("source"),
+    })).rejects.toMatchObject({ code: "material_preview_material_limit" });
+
+    await expect(store.createBundle({
+      actorId: "actor-1",
+      reimbursementId: "reimbursement-1",
+      expiresAt: Date.now() + 1_000,
+      materials: [
+        { id: "one", materialType: "invoice", materialIndex: 1, mimeType: "application/pdf", fileSize: 6 },
+      ],
+      readSource: async () => Buffer.from("source"),
+    })).rejects.toBeInstanceOf(MaterialPreviewError);
+  });
+});