diff --git a/packages/rest/src/export-business-timezone.test.ts b/packages/rest/src/export-business-timezone.test.ts
index c0a7be43c3..cde9ea5b44 100644
--- a/packages/rest/src/export-business-timezone.test.ts
+++ b/packages/rest/src/export-business-timezone.test.ts
@@ -31,13 +31,13 @@
  */
 
 import { describe, it, expect, beforeEach, afterEach } from 'vitest';
-import ExcelJS from 'exceljs';
 import { ObjectQL } from '@objectstack/objectql';
 import { SqlDriver } from '@objectstack/driver-sql';
 import { ObjectStackProtocolImplementation } from '@objectstack/metadata-protocol';
 import { RestServer } from './rest-server.js';
 import { formatCellValue, formatRowCells, formatRowForJson } from './export-format.js';
 import type { ExportFieldMeta } from './export-format.js';
+import { loadXlsxWorkbook } from './xlsx-test-loader.js';
 
 // The instant at the heart of the report: 2026-08-01 06:00 in +08 is
 // 2026-07-31 22:00 in UTC — a different day, month and quarter-of-year.
@@ -238,8 +238,7 @@ async function xlsxRow(timezone?: string): Promise<string[]> {
   const route = await boot(timezone);
   const { res, getBuffer } = makeBinRes();
   await route.handler({ params: { object: 'shift' }, query: { format: 'xlsx' } } as any, res);
-  const wb = new ExcelJS.Workbook();
-  await wb.xlsx.load(getBuffer() as any);
+  const wb = await loadXlsxWorkbook(getBuffer());
   return (wb.worksheets[0].getRow(2).values as any[]).slice(1).map((v) => String(v));
 }
 
diff --git a/packages/rest/src/export-integration.test.ts b/packages/rest/src/export-integration.test.ts
index 3673495f35..10660367b8 100644
--- a/packages/rest/src/export-integration.test.ts
+++ b/packages/rest/src/export-integration.test.ts
@@ -33,12 +33,12 @@
  */
 
 import { describe, it, expect, beforeEach, afterEach } from 'vitest';
-import ExcelJS from 'exceljs';
 import { ObjectQL } from '@objectstack/objectql';
 import { SqlDriver } from '@objectstack/driver-sql';
 import { ObjectStackProtocolImplementation } from '@objectstack/metadata-protocol';
 import { maskFieldValue } from '@objectstack/plugin-security';
 import { RestServer } from './rest-server';
+import { loadXlsxWorkbook } from './xlsx-test-loader.js';
 
 // ---------------------------------------------------------------------------
 // The real backend: better-sqlite3 `:memory:`, constructed the canonical way
@@ -211,8 +211,7 @@ describe('export route — real engine + protocol integration', () => {
     expect(headers['Content-Type']).toBe(
       'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
     );
-    const wb = new ExcelJS.Workbook();
-    await wb.xlsx.load(getBuffer() as any);
+    const wb = await loadXlsxWorkbook(getBuffer());
     const ws = wb.worksheets[0];
     const header = (ws.getRow(1).values as any[]).slice(1).map((v) => String(v));
     expect(header).toEqual(['ID', '标题', '完成', '优先级', '截止', '负责人']);
@@ -227,8 +226,7 @@ describe('export route — real engine + protocol integration', () => {
     // Default limit (10000) is within the style cap, so colours are applied.
     expect(headers['X-Export-Styles']).toBe('applied');
 
-    const wb = new ExcelJS.Workbook();
-    await wb.xlsx.load(getBuffer() as any);
+    const wb = await loadXlsxWorkbook(getBuffer());
     const ws = wb.worksheets[0];
     // priority is column 4 (ID, 标题, 完成, 优先级, ...).
     const highCell = ws.getRow(2).getCell(4); // '高' → #e11d48
@@ -247,8 +245,7 @@ describe('export route — real engine + protocol integration', () => {
     );
 
     expect(headers['X-Export-Styles']).toBe('dropped');
-    const wb = new ExcelJS.Workbook();
-    await wb.xlsx.load(getBuffer() as any);
+    const wb = await loadXlsxWorkbook(getBuffer());
     const ws = wb.worksheets[0];
     // Data is intact...
     const r1 = (ws.getRow(2).values as any[]).slice(1).map((v) => String(v));
@@ -528,8 +525,7 @@ describe('export route — FLS column projection via getReadableFields (#3547)',
     });
     const { res, getBuffer } = makeBinRes();
     await route.handler({ params: { object: 'task' }, query: { format: 'xlsx' } } as any, res);
-    const wb = new ExcelJS.Workbook();
-    await wb.xlsx.load(getBuffer() as any);
+    const wb = await loadXlsxWorkbook(getBuffer());
     const ws = wb.worksheets[0];
     expect((ws.getRow(1).values as any[]).slice(1)).toEqual(['ID', '完成']);
     expect(ws.rowCount).toBe(1); // header only
@@ -610,8 +606,7 @@ describe('export route — search', () => {
       { params: { object: 'task' }, query: { format: 'xlsx', search: '代码' } } as any,
       res,
     );
-    const wb = new ExcelJS.Workbook();
-    await wb.xlsx.load(getBuffer() as any);
+    const wb = await loadXlsxWorkbook(getBuffer());
     expect(wb.worksheets[0].rowCount).toBe(2); // header + one match
   });
 });
diff --git a/packages/rest/src/rest.test.ts b/packages/rest/src/rest.test.ts
index 4e2fe9ae11..10020c00d8 100644
--- a/packages/rest/src/rest.test.ts
+++ b/packages/rest/src/rest.test.ts
@@ -1,11 +1,11 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
-import ExcelJS from 'exceljs';
 import { RouteManager } from './route-manager';
 import { RestServer, mapDataError } from './rest-server';
 import { createRestApiPlugin } from './rest-api-plugin';
 import type { RestApiPluginConfig } from './rest-api-plugin';
+import { loadXlsxWorkbook } from './xlsx-test-loader.js';
 
 // ---------------------------------------------------------------------------
 // Mocks & Helpers
@@ -1263,8 +1263,7 @@ describe('RestServer', () => {
       // xlsx is a zip — verify the PK signature, then round-trip the content.
       expect(buf.subarray(0, 2).toString('latin1')).toBe('PK');
 
-      const wb = new ExcelJS.Workbook();
-      await wb.xlsx.load(buf);
+      const wb = await loadXlsxWorkbook(buf);
       const ws = wb.getWorksheet('Export');
       expect(ws).toBeDefined();
       // row.values is 1-indexed (values[0] is empty).
diff --git a/packages/rest/src/xlsx-test-loader.ts b/packages/rest/src/xlsx-test-loader.ts
new file mode 100644
index 0000000000..f3ce5889bf
--- /dev/null
+++ b/packages/rest/src/xlsx-test-loader.ts
@@ -0,0 +1,88 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * The one place this package asserts around `exceljs`'s broken `load` signature
+ * (#13378). Test layer only — nothing in `src/index.ts` reaches it, so tsup
+ * (entry: `src/index.ts`) never emits it into `dist` and it is not published.
+ *
+ * ## Why the assertion below is unavoidable, in the dependency's own bytes
+ *
+ * `exceljs@4.4.0/index.d.ts` opens, at line 1, with:
+ *
+ * ```ts
+ * declare interface Buffer extends ArrayBuffer { }
+ * ```
+ *
+ * That file carries 106 top-level `export` declarations, so it **is a module** —
+ * which makes this `Buffer` module-local, and it therefore SHADOWS Node's global
+ * `Buffer` inside every exceljs signature. The one that matters here is the
+ * `Xlsx.load` at `index.d.ts:1490`:
+ *
+ * ```ts
+ * load(buffer: Buffer, options?: Partial<XlsxReadOptions>): Promise<Workbook>;
+ * ```
+ *
+ * ⇒ `Workbook.xlsx.load` does not ask for a Node `Buffer`. It asks for something
+ * structurally identical to `ArrayBuffer`. A Node `Buffer` is a `Uint8Array`, so
+ * it is not assignable, and tsc says so precisely:
+ *
+ * ```
+ * src/rest.test.ts(1267,26): error TS2345: Argument of type 'Buffer<ArrayBuffer>' is not assignable to parameter of type 'Buffer'.
+ *   The types of 'slice(...)[Symbol.toStringTag]' are incompatible between these types.
+ *     Type '"Uint8Array"' is not assignable to type '"ArrayBuffer"'.
+ * ```
+ *
+ * ⭐ There is NO Node `Buffer` value that satisfies that parameter. The defect is
+ * in the published declaration, not at any call site — so this is not laziness,
+ * and no amount of care at a call site can remove it. What a call site CAN do is
+ * not restate it: before #13378 the package paid this at 6 anonymous `as any`s
+ * and left a 7th site as a ledgered `TS2345`. Now it is stated once, here.
+ *
+ * ## Why option C (upgrade) is not the answer — measured 2026-08-30
+ *
+ * `exceljs` `dist-tags.latest` IS 4.4.0 (published 2023-10-19). The only publish
+ * after it in the package's whole 166-version history is `4.4.1-prerelease.0`
+ * (2024-12-20), and its `index.d.ts` carries the identical declaration at the
+ * identical lines: shim at line 1, 106 exports, `load(buffer: Buffer, …)` at
+ * 1490. The registry's `time.modified` is that same date. There is no later line
+ * to pin to. (4.3.0 ships the shim too, so this is not a 4.4.0 regression that a
+ * bump could undo.)
+ *
+ * ## Why not a declaration override (option B)
+ *
+ * The `Buffer` above is module-local, so it cannot be reached by interface
+ * augmentation from outside; an override would have to redeclare the module,
+ * replacing the package's entire typing surface. Far more surface than the one
+ * assertion it would remove.
+ *
+ * ## Runtime is untouched
+ *
+ * exceljs's `load` has always accepted the Node `Buffer` these tests hand it —
+ * that is what every one of those 6 `as any` sites was doing, and passing. This
+ * helper changes only what tsc is told; it does not convert, copy or reshape the
+ * bytes.
+ */
+
+import ExcelJS from 'exceljs';
+import type { Workbook, Xlsx } from 'exceljs';
+
+/**
+ * The parameter type `Xlsx.load` actually declares, read off the dependency's
+ * own signature instead of spelled by hand. Naming it this way means that if
+ * exceljs ever drops the shim, this alias resolves to Node's `Buffer` and the
+ * assertion below quietly becomes a no-op rather than a lie.
+ */
+type XlsxLoadInput = Parameters<Xlsx['load']>[0];
+
+/**
+ * Load .xlsx bytes into a fresh {@link Workbook}.
+ *
+ * The single site in this package where the exceljs declaration defect above is
+ * asserted away. Callers pass the Node `Buffer` their fixture produced and get
+ * back a workbook; no call site needs to know about any of this.
+ */
+export async function loadXlsxWorkbook(bytes: Buffer): Promise<Workbook> {
+    const wb = new ExcelJS.Workbook();
+    await wb.xlsx.load(bytes as unknown as XlsxLoadInput);
+    return wb;
+}
diff --git a/packages/rest/test-typecheck-debt.json b/packages/rest/test-typecheck-debt.json
index cf3fc4cf3c..62004836f6 100644
--- a/packages/rest/test-typecheck-debt.json
+++ b/packages/rest/test-typecheck-debt.json
@@ -1,9 +1,9 @@
 {
   "_comment": "Per-file tsc error debt of the @objectstack/rest TEST layer (#5286). `tsconfig.test.json` compiles `src/**/*.test.ts` — which `tsconfig.json` excludes and therefore no gate ever read — and every file below still carries errors from before that gate existed. THIS FIELD IS GENERATED: every regeneration rewrites it from scripts/check-test-typecheck.mts, and the EXACT ratchet below requires a regeneration on every repair — so an edit made here is gone by the next one. Anything true of THIS package goes in the sibling `_note` field, which is authored, is preserved verbatim, and is never written by the generator (#12624). This comment states NO cause for the errors, deliberately: the classes differ per package and per file, they move as the debt is paid down, and a cause written here is rewritten verbatim into every ledger by every regeneration — so it outlives its own repair and cannot be corrected in the file where it is read. Measure instead, before repairing anything: `tsc --noEmit --pretty false -p tsconfig.test.json` in the package prints the real classes with their TS codes. EXACT ratchet, judged by re-running tsc: a file that gains errors is red, a file that loses them is red until its number is re-recorded, a file that reaches zero is red until its entry is deleted, and a file NOT listed here may have no errors at all. Regenerate with: pnpm --filter @objectstack/rest gen:test-typecheck-debt",
-  "_note": "Everything still recorded here is held by its own card, and none of it is an annotation repair. #13377 holds the request literals this package builds by hand against IHttpRequest, which omit members that interface requires. #13378 holds the exceljs call whose parameter type resolves to that package's own module-local Buffer declaration rather than Node's. Repairing either one here would mean changing a fixture's data, or adding an assertion this package's paydown rules out, so these entries shrink when those cards land and not before.",
+  "_note": "Everything still recorded here is held by its own card, and none of it is an annotation repair. #13377 holds every entry that remains: the request literals this package builds by hand against IHttpRequest, which omit members that interface requires. Repairing them here would mean changing a fixture's data, so these entries shrink when that card lands and not before. The exceljs call that #13378 held is no longer in this ledger: that dependency declares its own module-local Buffer, which shadows Node's inside every exceljs signature, so no Node Buffer can be passed to Workbook.xlsx.load — the assertion that costs is now stated once, in src/xlsx-test-loader.ts, and every xlsx-reading test in this package goes through it.",
   "entries": {
     "src/meta-public-book-grant.test.ts": 1,
     "src/rest-batch-size-cap.test.ts": 1,
-    "src/rest.test.ts": 3
+    "src/rest.test.ts": 2
   }
 }