fix: prevent navigation to .txt URLs when RSC payload fetch fails in static export

packages/next/src/client/components/router-reducer/fetch-server-response.ts

@@ -240,14 +240,7 @@ export async function fetchServerResponse(
     // If fetch fails handle it like a mpa navigation
     // TODO-APP: Add a test for the case where a CORS request fails, e.g. external url redirect coming from the response.
     // See https://github.com/vercel/next.js/issues/43605#issuecomment-1451617521 for a reproduction.
-    return {
-      flightData: url.toString(),
-      canonicalUrl: undefined,
-      couldBeIntercepted: false,
-      prerendered: false,
-      postponed: false,
-      staleTime: -1,
-    }
+    return doMpaNavigation(url.toString())
   }
 }
 

test/e2e/app-dir/segment-cache/export/segment-cache-output-export.test.ts

@@ -160,4 +160,57 @@ describe('segment cache (output: "export")', () => {
       }
     )
   })
+
+  it('fallback to HTML navigation when RSC payload fetch fails in output: "export" mode', async () => {
+    // This test verifies that when RSC payload fetching fails (e.g., .txt files are blocked),
+    // the navigation falls back to regular HTML navigation without .txt extension
+    let act
+    const browser = await webdriver(port, '/', {
+      beforePageLoad(p: Playwright.Page) {
+        act = createRouterAct(p)
+        // Block .txt requests at the network level to simulate RSC payload fetch failures
+        p.route('**/*.txt', (route) => route.abort())
+      },
+    })
+
+    // Initiate a prefetch
+    await act(
+      async () => {
+        const checkbox = await browser.elementByCss(
+          '[data-link-accordion="/target-page"]'
+        )
+        await checkbox.click()
+      },
+      {
+        includes: 'Target page',
+      }
+    )
+
+    // Navigate to the prefetched target page.
+    await act(
+      async () => {
+        const link = await browser.elementByCss('a[href="/target-page"]')
+        await link.click()
+
+        // Wait for navigation to complete
+        await browser.waitForCondition(
+          'document.location.pathname.includes("target-page") && document.body.textContent.includes("Target page")',
+          5000
+        )
+
+        // Verify that we navigated to the correct HTML page, not .txt
+        const currentUrl = await browser.url()
+        expect(currentUrl).not.toContain('.txt')
+        expect(new URL(currentUrl).pathname).toBe('/target-page')
+
+        // Verify page content is displayed
+        const bodyText = await browser.eval('document.body.textContent')
+        expect(bodyText).toContain('Target page')
+      },
+      {
+        // Should have prefetched the home page
+        includes: 'Demonstrates that per-segment prefetching works',
+      }
+    )
+  })
 })