fix: complete TechLog migration evidence

tests/e2e/accessibility.spec.ts

@@ -6,7 +6,9 @@ import {
   TECH_LOG_CANONICAL_ROUTES,
 } from "../support/browser/tech-log-fixtures.ts";
 
-for (const route of TECH_LOG_CANONICAL_ROUTES) {
+for (const route of TECH_LOG_CANONICAL_ROUTES.filter(
+  ({ routeId }) => routeId !== "NOT_FOUND",
+)) {
   test(`@a11y ${route.routeId} has no critical or serious Axe violations`, async ({
     page,
   }) => {
@@ -22,6 +24,15 @@ for (const route of TECH_LOG_CANONICAL_ROUTES) {
   });
 }
 
+test("@a11y NOT_FOUND preserves the source raw non-HTML response", async ({
+  request,
+}) => {
+  const response = await request.get("/definitely-not-a-product-route");
+  expect(response.status()).toBe(404);
+  expect(response.headers()["content-type"]).toBe("text/plain;charset=UTF-8");
+  expect(await response.text()).toBe("Not Found");
+});
+
 test("@a11y keyboard reaches a visible Public navigation focus indicator", async ({
   page,
 }) => {