diff --git a/src/domain/work-orders/api/work-order-board-documents-api.ts b/src/domain/work-orders/api/work-order-board-documents-api.ts
index 99c060fd..fbd7bf77 100644
--- a/src/domain/work-orders/api/work-order-board-documents-api.ts
+++ b/src/domain/work-orders/api/work-order-board-documents-api.ts
@@ -216,10 +216,14 @@ export const workOrderBoardDocumentsApi = {
     workOrderId: string | number,
     mediaId: string | number,
   ): Promise<Blob> => {
+    // No `credentials: "include"`: this endpoint authenticates with the bearer token the ky
+    // beforeRequest hook attaches, not cookies. In credentialed mode the browser rejects the
+    // API's `Access-Control-Allow-Origin: *` outright, so the fetch would throw and the document
+    // would never open.
     const response = await apiRequestRaw(
       "get",
       API_PATHS.workOrder.mediaContent(workOrderId, mediaId),
-      { credentials: "include", throwHttpErrors: false },
+      { throwHttpErrors: false },
       "workOrderBoardDocumentsApi.getMediaContent",
     );
 
diff --git a/src/test/domain/work-orders/api/work-orders-api.test.ts b/src/test/domain/work-orders/api/work-orders-api.test.ts
index e295ed9d..cbfabfa9 100644
--- a/src/test/domain/work-orders/api/work-orders-api.test.ts
+++ b/src/test/domain/work-orders/api/work-orders-api.test.ts
@@ -1022,8 +1022,14 @@ describe("workOrdersApi.getMediaContent", () => {
     expect(result).toBe(blob);
     expect(apiGetFn).toHaveBeenCalledWith(
       API_PATHS.workOrder.mediaContent(10, 12),
-      expect.objectContaining({ credentials: "include", throwHttpErrors: false }),
+      expect.objectContaining({ throwHttpErrors: false }),
     );
+    // Regression guard (SH-382): a credentialed cross-origin fetch is rejected by the browser
+    // against the API's `Access-Control-Allow-Origin: *`, so the content request must not opt
+    // into credentials mode — otherwise the document never opens. JSDOM cannot enforce CORS, so
+    // this asserts the request shape rather than reproducing the block.
+    const [, options] = apiGetFn.mock.calls[0] as [string, Record<string, unknown>];
+    expect(options).not.toHaveProperty("credentials");
   });
 
   it("throws ApiError on 404 without inventing a filename", async () => {