test(desktop): make the Playwright e2e suite runnable on Windows

desktop/playwright.config.ts

@@ -1,5 +1,7 @@
 import { defineConfig, devices } from "@playwright/test";
 
+import { staticWebServer } from "./tests/helpers/staticWebServer";
+
 export default defineConfig({
   testDir: "./tests/e2e",
   timeout: 30_000,
@@ -174,10 +176,5 @@ export default defineConfig({
       },
     },
   ],
-  webServer: {
-    command: "python3 -m http.server 4173 -d dist",
-    cwd: ".",
-    reuseExistingServer: !process.env.CI,
-    url: "http://127.0.0.1:4173",
-  },
+  webServer: staticWebServer({ reuseExistingServer: !process.env.CI }),
 });

desktop/playwright.perf.config.ts

@@ -1,5 +1,7 @@
 import { defineConfig, devices } from "@playwright/test";
 
+import { staticWebServer } from "./tests/helpers/staticWebServer";
+
 export default defineConfig({
   testDir: "./tests/e2e",
   timeout: 60_000,
@@ -14,10 +16,5 @@ export default defineConfig({
       use: { ...devices["Desktop Chrome"] },
     },
   ],
-  webServer: {
-    command: "python3 -m http.server 4173 -d dist",
-    cwd: ".",
-    reuseExistingServer: true,
-    url: "http://127.0.0.1:4173",
-  },
+  webServer: staticWebServer({ reuseExistingServer: true }),
 });

desktop/tests/e2e/messaging.spec.ts

@@ -993,8 +993,17 @@ test("copy a rendered code block and paste it back as code", async ({
   await codeBlock.hover();
   await expect(copyButton).toHaveCSS("opacity", "1");
   await copyButton.click();
+  // Chromium hands back CRLF when it reads text/plain off the Windows
+  // clipboard, so compare logical lines rather than the platform separator.
+  // The app writes LF: `copyCodeBlockToClipboard` puts `code` in the blob
+  // verbatim.
   await expect
-    .poll(() => page.evaluate(() => navigator.clipboard.readText()))
+    .poll(async () =>
+      (await page.evaluate(() => navigator.clipboard.readText())).replace(
+        /\r\n/g,
+        "\n",
+      ),
+    )
     .toBe(code);
 
   await input.click();

desktop/tests/helpers/staticWebServer.ts

@@ -0,0 +1,40 @@
+import { spawnSync } from "node:child_process";
+
+const PORT = 4173;
+
+/**
+ * `python3` is the right name on Linux and macOS. On Windows it is normally
+ * the Microsoft Store app-execution alias, which prints an install hint and
+ * exits 9009 even when a real interpreter is installed as `python`. Playwright
+ * then reports only `Process from config.webServer was not able to start.
+ * Exit code: 9009`, so the suite cannot be run at all on a stock Windows box.
+ *
+ * Probe the candidates rather than guessing. `-c ""` is a no-op that a real
+ * interpreter accepts and the alias stub rejects.
+ */
+function resolvePythonCommand() {
+  const candidates =
+    process.platform === "win32"
+      ? ["python", "python3"]
+      : ["python3", "python"];
+
+  for (const candidate of candidates) {
+    const probe = spawnSync(candidate, ["-c", ""], { stdio: "ignore" });
+    if (!probe.error && probe.status === 0) {
+      return candidate;
+    }
+  }
+
+  // Nothing answered. Keep the historical name so the failure still points at
+  // the missing interpreter instead of at this helper.
+  return "python3";
+}
+
+export function staticWebServer(options: { reuseExistingServer: boolean }) {
+  return {
+    command: `${resolvePythonCommand()} -m http.server ${PORT} -d dist`,
+    cwd: ".",
+    reuseExistingServer: options.reuseExistingServer,
+    url: `http://127.0.0.1:${PORT}`,
+  };
+}