完善借款、编号、付款与预算并发及验收（09-06-release-gate-integrity）

汇总已落盘的借款本金与还款、兼容历史编号的周期化编号、付款责任与回单核验、报销进度和排序、PWA/采购事务、错误原因与日期校验及ERP退役。
统一共享预算池锁序和锁后判断，恢复差旅原预算选择，补原因码固定夹具及反向完整性检查。
纳入配套迁移、测试、受管QA、分层验收合同、规约及任务记录；原始证据留在ignored artifacts。

关联任务：09-17-company-loan-principal-repayment、09-17-erp-exclusive-retirement、09-18-reimbursement-periodic-numbering、09-08-reimbursement-payment-closeout、09-18-local-concurrency-product-fixes、09-19-budget-pool-concurrency、09-05-error-explainability-payment-readiness。
预算补审由Claude定向验证2文件928项通过，原4446/28及r6结果仍仅对应各自历史输入；本轮未重跑测试。
完整新候选门禁、R1真实入口接入与12项公网义务仍开放。生产编号未启用、差旅仍冻结；不推送、不部署，不宣称发布资格。

server/tests/unit/routes/payroll.payslips.test.js

@@ -351,6 +351,7 @@ describe("payroll payslip routes", () => {
     });
 
     expect(frozenResponse.statusCode).toBe(409);
+    expect(frozenResponse.json().error.details).toEqual({ payslip: "payslip_not_editable", reasonCode: "payroll.payslip_not_editable" });
 
     await app.close();
 
@@ -388,8 +389,111 @@ describe("payroll payslip routes", () => {
 
     expect(response.statusCode).toBe(409);
     expect(response.json().error.details.month).toBe("salary_profile_missing");
+    expect(response.json().error.details.reasonCode).toBe("payroll.profiles_missing");
     expect(state.payslips).toHaveLength(0);
 
     await app.close();
   });
 });
+
+describe("payroll month guards", () => {
+  it.each(["2026-00", "2026-13", "2026-1", "invalid", ""].flatMap((month) => [
+    ["GET", "/api/payroll/payslips", month],
+    ["POST", "/api/payroll/payslips/generate", month],
+    ["POST", "/api/payroll/payslips/issue", month],
+  ]))("rejects %s %s month=%s before business access", async (method, url, month) => {
+    const { app } = await buildApp();
+    try {
+      const response = await app.inject({ method, url: method === "GET" ? `${url}?month=${month}` : url, ...(method === "POST" ? { payload: { month } } : {}) });
+      expect(response.statusCode).toBe(400);
+      expect(response.json().error.code).toBe("VALID_001");
+      expect(response.json().error.details.reasonCode).toBe("payroll.month_invalid");
+      if (["2026-00", "2026-13"].includes(month)) expect(response.json().error.details).toEqual({ month: "invalid_month", reasonCode: "payroll.month_invalid" });
+      for (const [key, group] of Object.entries(app.prisma)) {
+        if (key === "$transaction") expect(group).not.toHaveBeenCalled();
+        else for (const fn of Object.values(group)) expect(fn).not.toHaveBeenCalled();
+      }
+    } finally { await app.close(); }
+  });
+
+  it.each(["2024-01", "2024-02", "2024-12"])("queries the exact UTC month for %s", async (month) => {
+    const { app } = await buildApp();
+    try {
+      const response = await app.inject({ method: "GET", url: `/api/payroll/payslips?month=${month}` });
+      expect(response.statusCode).toBe(200);
+      expect(response.json().data.month).toBe(month);
+      expect(app.prisma.payslip.findMany.mock.calls[0][0].where.pay_month).toEqual(new Date(`${month}-01T00:00:00.000Z`));
+    } finally { await app.close(); }
+  });
+});
+
+describe("payslip operation reasons", () => {
+  function expectNoWrites(app) {
+    for (const fn of [app.prisma.payslip.create, app.prisma.payslip.update, app.prisma.payslip.updateMany, app.prisma.payslipItem.createMany, app.prisma.payslipItem.deleteMany, app.prisma.auditLog.create]) {
+      expect(fn).not.toHaveBeenCalled();
+    }
+  }
+  it.each([
+    ["already_generated", "month_already_generated", { month: "payslips_month_exists" }],
+    ["no_employees", "active_employees_missing", { month: "no_active_employees" }],
+    ["no_items", "enabled_items_missing", { items: "salary_items_empty" }],
+  ])("explains generation blocker %s before writes", async (scenario, reason, details) => {
+    const { app, state } = await buildApp();
+    if (scenario === "already_generated") state.payslips.push({ pay_month: new Date("2026-04-01T00:00:00.000Z") });
+    if (scenario === "no_employees") state.employees.length = 0;
+    if (scenario === "no_items") state.salaryItems.length = 0;
+    try {
+      const response = await app.inject({ method: "POST", url: "/api/payroll/payslips/generate", payload: { month: "2026-04" } });
+      expect(response.statusCode).toBe(409);
+      expect(response.json().error.details).toEqual({ ...details, reasonCode: `payroll.${reason}` });
+      expectNoWrites(app);
+    } finally { await app.close(); }
+  });
+  it("explains a concurrent month uniqueness conflict without success audit", async () => {
+    const { app } = await buildApp();
+    app.prisma.payslip.create.mockRejectedValueOnce(Object.assign(new Error("synthetic conflict"), { code: "P2002" }));
+    try {
+      const response = await app.inject({ method: "POST", url: "/api/payroll/payslips/generate", payload: { month: "2026-04" } });
+      expect(response.statusCode).toBe(409);
+      expect(response.json().error.details).toEqual({ month: "payslips_month_exists", reasonCode: "payroll.month_already_generated" });
+      expect(app.prisma.payslipItem.createMany).not.toHaveBeenCalled();
+      expect(app.prisma.auditLog.create).not.toHaveBeenCalled();
+    } finally { await app.close(); }
+  });
+  it.each([false, true])("explains issue rejection with existing issued slips=%s", async (existing) => {
+    const { app, state } = await buildApp();
+    if (existing) state.payslips.push({ id: PAYSLIP_IDS[0], pay_month: new Date("2026-04-01T00:00:00.000Z"), status: "issued" });
+    try {
+      const response = await app.inject({ method: "POST", url: "/api/payroll/payslips/issue", payload: { month: "2026-04" } });
+      expect(response.statusCode).toBe(409);
+      expect(response.json().error.details).toEqual({ month: existing ? "payslips_already_issued" : "payslips_not_generated", reasonCode: existing ? "payroll.month_already_issued" : "payroll.month_not_generated" });
+      expectNoWrites(app);
+    } finally { await app.close(); }
+  });
+  it.each([
+    [{ items: [] }, "payroll.payslip_update_input_invalid"],
+    [{ items: [{ salaryItemId: "11111111-1111-4111-8111-111111111111", amount: "1.234" }] }, "payroll.amount_invalid"],
+  ])("explains invalid payslip edit %j before reads", async (payload, reasonCode) => {
+    const { app } = await buildApp();
+    try {
+      const response = await app.inject({ method: "PATCH", url: `/api/payroll/payslips/${PAYSLIP_IDS[0]}`, payload });
+      expect(response.statusCode).toBe(400);
+      expect(response.json().error.details.reasonCode).toBe(reasonCode);
+      if (reasonCode === "payroll.amount_invalid") expect(response.json().error.details).toEqual({ items: { 0: { amount: "invalid_money_amount" } }, reasonCode });
+      expect(app.prisma.payslip.findUnique).not.toHaveBeenCalled();
+      expectNoWrites(app);
+    } finally { await app.close(); }
+  });
+  it("explains an unavailable item in an editable payslip before replacement", async () => {
+    const { app, state } = await buildApp();
+    state.payslips.push({ id: PAYSLIP_IDS[0], pay_month: new Date("2026-04-01T00:00:00.000Z"), employee_id: EMPLOYEE_ID, status: "draft" });
+    app.prisma.salaryItem.findMany.mockResolvedValueOnce([]);
+    try {
+      const response = await app.inject({ method: "PATCH", url: `/api/payroll/payslips/${PAYSLIP_IDS[0]}`, payload: { items: [{ salaryItemId: "11111111-1111-4111-8111-111111111111", amount: 100 }] } });
+      expect(response.statusCode).toBe(400);
+      expect(response.json().error.details).toEqual({ items: "salary_item_not_found", reasonCode: "payroll.item_not_found" });
+      expectNoWrites(app);
+      expect(app.prisma.$transaction).not.toHaveBeenCalled();
+    } finally { await app.close(); }
+  });
+});