diff --git a/electron/applicationMenu.js b/electron/applicationMenu.js
new file mode 100644
index 00000000..6673c584
--- /dev/null
+++ b/electron/applicationMenu.js
@@ -0,0 +1,81 @@
+// Cmd+C works in every window, not just the first (ENG-289).
+//
+// The app never called setApplicationMenu, so macOS was left with Electron's implicit default and
+// the Edit accelerators were whatever that happened to bind. The menu is process-global while its
+// items act on whichever webContents holds focus, so "which window" is decided at keypress time by
+// role dispatch, not by whatever window the menu was built next to. Declaring the menu ourselves
+// makes that dispatch explicit and identical in the first window and the tenth.
+//
+// ROLES ONLY, deliberately. A hand-written copy handler has to answer "copy from where", and the
+// answer is a focused-webContents lookup that is wrong for a <webview> guest exactly when the user
+// is inside one. Chromium already resolves roles against the focused contents, including guests,
+// so the correct implementation is the one where we write no logic at all.
+//
+// macOS only: on Windows and Linux setting a menu paints a visible menu bar this app has never had.
+
+const APP_NAME = 'OpenSwarm';
+
+/** The template, separated from the Electron call so it can be asserted without an app instance. */
+function applicationMenuTemplate() {
+  return [
+    {
+      label: APP_NAME,
+      submenu: [
+        { role: 'about' },
+        { type: 'separator' },
+        { role: 'services' },
+        { type: 'separator' },
+        { role: 'hide' },
+        { role: 'hideOthers' },
+        { role: 'unhide' },
+        { type: 'separator' },
+        { role: 'quit' },
+      ],
+    },
+    {
+      label: 'Edit',
+      submenu: [
+        { role: 'undo' },
+        { role: 'redo' },
+        { type: 'separator' },
+        { role: 'cut' },
+        { role: 'copy' },
+        { role: 'paste' },
+        { role: 'pasteAndMatchStyle' },
+        { role: 'delete' },
+        { role: 'selectAll' },
+      ],
+    },
+    {
+      label: 'View',
+      submenu: [
+        { role: 'reload' },
+        { role: 'forceReload' },
+        { type: 'separator' },
+        { role: 'resetZoom' },
+        { role: 'zoomIn' },
+        { role: 'zoomOut' },
+        { type: 'separator' },
+        { role: 'togglefullscreen' },
+      ],
+    },
+    {
+      label: 'Window',
+      submenu: [
+        { role: 'minimize' },
+        { role: 'zoom' },
+        { type: 'separator' },
+        { role: 'front' },
+      ],
+    },
+  ];
+}
+
+function installApplicationMenu(electron) {
+  if (process.platform !== 'darwin') return false;
+  const { Menu } = electron;
+  Menu.setApplicationMenu(Menu.buildFromTemplate(applicationMenuTemplate()));
+  return true;
+}
+
+module.exports = { applicationMenuTemplate, installApplicationMenu, APP_NAME };
diff --git a/electron/applicationMenu.test.js b/electron/applicationMenu.test.js
new file mode 100644
index 00000000..8023e257
--- /dev/null
+++ b/electron/applicationMenu.test.js
@@ -0,0 +1,65 @@
+// Run: node --test electron/applicationMenu.test.js
+//
+// ENG-289: "open a second window, select text, Cmd+C, nothing is copied; the same steps in the
+// first window work." The app never declared an application menu, so the Edit accelerators were
+// whatever Electron's implicit default bound. The menu is process-global and its items act on the
+// FOCUSED webContents, so declaring it ourselves is what makes the second window behave like the
+// first.
+//
+// These assert the two properties that decide whether the bug can come back: the Edit accelerators
+// exist at all, and they are ROLES (Chromium resolves those against the focused contents, including
+// a <webview> guest) rather than hand-written handlers that have to guess at a target.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const { applicationMenuTemplate, installApplicationMenu } = require('./applicationMenu');
+
+function editSubmenu() {
+  const edit = applicationMenuTemplate().find((m) => m.label === 'Edit');
+  assert.ok(edit, 'there must be an Edit menu; it is what binds Cmd+C on macOS');
+  return edit.submenu;
+}
+
+test('the clipboard accelerators are all present', () => {
+  const roles = editSubmenu().map((i) => i.role).filter(Boolean);
+  for (const needed of ['copy', 'cut', 'paste', 'selectAll', 'undo', 'redo']) {
+    assert.ok(roles.includes(needed), `Edit menu is missing the ${needed} role`);
+  }
+});
+
+test('clipboard items are roles, never hand-written click handlers', () => {
+  // A click handler would have to resolve "copy from where" itself, and that lookup is wrong for a
+  // webview guest exactly when the user is typing inside one.
+  for (const item of editSubmenu()) {
+    if (item.type === 'separator') continue;
+    assert.ok(item.role, `Edit item ${JSON.stringify(item)} must be a role`);
+    assert.equal(item.click, undefined, `Edit item ${item.role} must not carry a click handler`);
+  }
+});
+
+test('no item pins itself to a specific window', () => {
+  const json = JSON.stringify(applicationMenuTemplate());
+  assert.ok(!json.includes('mainWindow'), 'a menu bound to one window is exactly the reported bug');
+  assert.ok(!json.includes('webContents'), 'roles resolve the target themselves; do not capture one');
+});
+
+test('the menu is installed on macOS and skipped elsewhere', () => {
+  const calls = [];
+  const fake = { Menu: { setApplicationMenu: (m) => calls.push(m), buildFromTemplate: (t) => t } };
+  const real = process.platform;
+  try {
+    Object.defineProperty(process, 'platform', { value: 'darwin', configurable: true });
+    assert.equal(installApplicationMenu(fake), true);
+    assert.equal(calls.length, 1, 'macOS must get an explicit menu');
+    Object.defineProperty(process, 'platform', { value: 'win32', configurable: true });
+    assert.equal(installApplicationMenu(fake), false, 'Windows would paint a menu bar this app never had');
+    assert.equal(calls.length, 1);
+  } finally {
+    Object.defineProperty(process, 'platform', { value: real, configurable: true });
+  }
+});
+
+test('main.js actually installs it', () => {
+  const src = require('fs').readFileSync(require('path').join(__dirname, 'main.js'), 'utf8');
+  assert.match(src, /installApplicationMenu/, 'a menu module nothing calls fixes nothing');
+});
diff --git a/electron/main.js b/electron/main.js
index 16495c53..8e95e706 100644
--- a/electron/main.js
+++ b/electron/main.js
@@ -2267,6 +2267,9 @@ ipcMain.handle('haptic:perform', (event, pattern) => {
 });
 
 app.whenReady().then(async () => {
+  // Declare the Edit accelerators instead of inheriting whatever the implicit default bound, so
+  // Cmd+C acts on the focused window rather than only the first one (ENG-289). macOS only.
+  try { require('./applicationMenu').installApplicationMenu(require('electron')); } catch (_) {}
   // We made it here, so any prior update swap finished. Drop a stale updating.lock
   // (the watchdog never deletes it) so a real crash later isn't silently swallowed.
   try { fs.unlinkSync(CRASH_WATCHDOG_UPDATING_LOCK); } catch (_) {}