test(main): cover the download and copy error-status paths

Exercises the toBlob-fails and clipboard.write-rejects branches of
download()/copyImage(), which were previously only reachable by
inspection. Also scopes coverage collection to src/** so tooling
config files don't skew the report.

Author: ctkrug

test/main.test.js

@@ -230,4 +230,35 @@ describe("app bootstrap and generate flow", () => {
     expect(writtenItems).not.toBeNull();
     expect(document.getElementById("output-status").textContent).toMatch(/copied/i);
   });
+
+  it("shows a designed error status when the download blob export fails", async () => {
+    document.getElementById("before-input").value = "const x = 1;";
+    document.getElementById("after-input").value = "const x = 2;";
+    const { api } = await loadMain();
+    api.generate();
+
+    HTMLCanvasElement.prototype.toBlob = function toBlob(callback) {
+      callback(null);
+    };
+
+    await api.download();
+
+    expect(document.getElementById("output-status").textContent).toMatch(/couldn't download/i);
+  });
+
+  it("shows a designed error status when the clipboard write rejects", async () => {
+    stubClipboardApis({
+      write: async () => {
+        throw new Error("clipboard denied");
+      },
+    });
+    document.getElementById("before-input").value = "const x = 1;";
+    document.getElementById("after-input").value = "const x = 2;";
+    const { api } = await loadMain();
+    api.generate();
+
+    await api.copyImage();
+
+    expect(document.getElementById("output-status").textContent).toMatch(/couldn't copy/i);
+  });
 });

vitest.config.js

@@ -9,5 +9,10 @@ export default defineConfig({
     // vitest's default include glob would otherwise try (and fail) to
     // collect them as unit tests.
     exclude: ["**/node_modules/**", "e2e/**"],
+    coverage: {
+      // Coverage should measure app source, not tooling config files that
+      // happen to sit at the repo root (vite/vitest/playwright configs).
+      include: ["src/**"],
+    },
   },
 });