test: add e2e for fetch error recovery via drop

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hi-ogawa

e2e/basic.spec.ts

@@ -14,6 +14,14 @@ test("file input", async ({ page }) => {
   await testHtmlReport(page);
 });
 
+test("fetch error clears on drop recovery", async ({ page }) => {
+  await page.goto("/?url=http://localhost:1/test.zip");
+  await expect(page.getByTestId("fetch-error")).toContainText("likely blocked by CORS");
+  await page.locator('input[type="file"]').setInputFiles("docs/assets/vitest-html-reporter.zip");
+  await expect(page.getByTestId("fetch-error")).not.toBeVisible();
+  await testHtmlReport(page);
+});
+
 async function testHtmlReport(page: Page) {
   await expect(page.getByTestId("status")).toContainText("Cached 7 files");
   const frame = page.frameLocator("iframe");

src/index.html

@@ -209,7 +209,10 @@
       function FetchError({ error }) {
         return h(
           "div",
-          { style: { textAlign: "center", fontSize: "0.85rem", color: "#c00", marginTop: "1rem" } },
+          {
+            "data-testid": "fetch-error",
+            style: { textAlign: "center", fontSize: "0.85rem", color: "#c00", marginTop: "1rem" },
+          },
           h("div", null, error.message),
           h(
             "div",