Default MCP tab tools to the active tab

Requiring an explicit tab_id forced every navigate or close through a
preceding tabs_list call, which costs an MCP client a full round trip just to
learn the ID the browser already considers current.

navigate and tabs_close now resolve the active tab when tab_id is omitted,
matching the screenshot tool. Resolution is explicit rather than forwarding
None into the SDK, so the acting tool knows which tab it touched; tabs_close
reports it, since closing the wrong tab is not recoverable.

This stays in the MCP layer: the SDK and CLI signatures are unchanged.

extension/test/windows.test.ts

@@ -0,0 +1,69 @@
+// @ts-nocheck
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { WindowsCommands } from '../src/commands/windows';
+import { makeChromeMock } from './chrome-mock';
+
+function makeWindowsChromeMock(windows) {
+  const chrome = makeChromeMock();
+  chrome.windows = {
+    getAll: async () => windows,
+    remove: async () => {},
+    create: async () => ({ id: 99 }),
+  };
+  return chrome;
+}
+
+test('windows.list prunes aliases for closed windows', async () => {
+  globalThis.chrome = makeWindowsChromeMock([
+    { id: 1, focused: true, state: 'normal', tabs: [{ id: 10 }] },
+    { id: 2, focused: false, state: 'minimized', tabs: [] },
+  ]);
+  globalThis.chrome.storage.local._store.windowAliases = {
+    1: 'main',
+    2: 'side',
+    999: 'closed',
+  };
+
+  const commands = new WindowsCommands({ jobs: {} });
+  const result = await commands.commands['windows.list']({});
+
+  assert.deepEqual(result.map(w => [w.id, w.alias]), [[1, 'main'], [2, 'side']]);
+  assert.deepEqual(globalThis.chrome.storage.local._store.windowAliases, { 1: 'main', 2: 'side' });
+});
+
+test('windows.rename prunes stale aliases before saving the new name', async () => {
+  globalThis.chrome = makeWindowsChromeMock([
+    { id: 1, focused: true, state: 'normal', tabs: [] },
+    { id: 2, focused: false, state: 'normal', tabs: [] },
+  ]);
+  globalThis.chrome.storage.local._store.windowAliases = {
+    1: 'main',
+    999: 'closed',
+  };
+
+  const commands = new WindowsCommands({ jobs: {} });
+  await commands.commands['windows.rename']({ windowId: 2, name: 'work' });
+
+  assert.deepEqual(globalThis.chrome.storage.local._store.windowAliases, { 1: 'main', 2: 'work' });
+});
+
+test('windows.close removes the closed window alias immediately', async () => {
+  let removed = null;
+  globalThis.chrome = makeWindowsChromeMock([
+    { id: 1, focused: true, state: 'normal', tabs: [] },
+    { id: 2, focused: false, state: 'normal', tabs: [] },
+  ]);
+  globalThis.chrome.windows.remove = async id => { removed = id; };
+  globalThis.chrome.storage.local._store.windowAliases = {
+    1: 'main',
+    2: 'side',
+    999: 'closed',
+  };
+
+  const commands = new WindowsCommands({ jobs: {} });
+  await commands.commands['windows.close']({ windowId: 2 });
+
+  assert.equal(removed, 2);
+  assert.deepEqual(globalThis.chrome.storage.local._store.windowAliases, { 1: 'main' });
+});