feat(i18n): the tab's exited-agent badge in Chinese (zh-CN)

Owner request: translate the EXITED badge. The badge carried
data-i18n-skip on purpose, because its in-place update compared the DOM
with the English label: a translated badge would never have matched, and
every incremental tab pass would have written English back for the
translator to redo. The tab's accessible name (which carries the exit,
the badge being aria-hidden) was set unconditionally on every pass, the
same trap once it is translated.

Now the badge is left to the translator. applyPaneExitBadge remembers the
last English badge text (data-label) and accessible name
(data-aria-source), both also seeded by the full render, and compares
with those, never the DOM. The tab strip's incremental path updates tabs
in place (no row-HTML comparison), so nothing else re-renders on a
translated badge.

i18n.js: "exited" -> 已退出, patterns for "exited (N)" -> 已退出（N） and
"exited (signal N)" -> 已退出（信号 N）, and for the accessible name
"<name> session, agent exited ..." -> "<name> 会话，智能体已退出 ...", the
session name passed through untranslated. The header strip, the session
sidebar and the vertical rail all host the same tab markup, so this
covers all three. English reads exactly as before.

Tests: session-pane-exit-ui pins the new markup, the remembered English
and that a translated badge and accessible name survive an unchanged
pass; i18n-exit-run-help runs every paneExitLabel form (and the
accessible name, with names that are dictionary words) through the real
translator in both languages.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/i18n-exit-run-help.test.ts

@@ -0,0 +1,80 @@
+/**
+ * @fileoverview zh-CN coverage for the tab's exited-agent badge (and the tab's
+ * accessible name that carries it).
+ *
+ * Every form `paneExitLabel()` produces (plain, an exit code, a negative code,
+ * a signal) must translate fully through i18n.js's real `t()`, with the
+ * session name in the accessible name passed through untranslated (a name
+ * that is itself a dictionary word included), and read unchanged in English.
+ *
+ * Port: N/A.
+ */
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import vm from 'node:vm';
+import { JSDOM } from 'jsdom';
+import { afterAll, describe, expect, it } from 'vitest';
+
+const PUBLIC = resolve(import.meta.dirname, '../src/web/public');
+const read = (f: string) => readFileSync(resolve(PUBLIC, f), 'utf8');
+const I18N = read('i18n.js');
+const APP = read('app.js');
+
+type Api = { t(s: string): string; configure(o: Record<string, string>): void };
+function translator(language: string) {
+  const dom = new JSDOM('<!doctype html><html><body></body></html>', {
+    runScripts: 'outside-only',
+    url: 'http://localhost/',
+  });
+  vm.runInContext(I18N, dom.getInternalVMContext(), { filename: 'i18n.js' });
+  const api = (dom.window as unknown as { CodemanI18n: Api }).CodemanI18n;
+  api.configure({ language });
+  return { api, dom };
+}
+const zh = translator('zh-CN');
+const en = translator('en');
+afterAll(() => {
+  zh.dom.window.close();
+  en.dom.window.close();
+});
+
+/** Latin words left after removing what may stay (key names). */
+const leftover = (text: string) =>
+  text.replace(/\b(Ctrl|Cmd|Shift|Alt|Option|Enter|Tab|Space|End|Home|Escape|G)\b/g, '').match(/[A-Za-z]+/g) ?? [];
+
+const helpers = new Function(
+  `${APP.match(/function paneExitLabel\([\s\S]*?\n\}/)![0]}\n${APP.match(/function paneExitAriaLabel\([\s\S]*?\n\}/)![0]}\n` +
+    'return { paneExitLabel, paneExitAriaLabel };'
+)() as { paneExitLabel(p: unknown): string; paneExitAriaLabel(name: string, label: string): string };
+
+const EXITS = [{}, { status: 0 }, { status: 3 }, { status: 137 }, { status: -1 }, { signal: 9 }];
+
+describe('the exited-agent badge in zh-CN', () => {
+  const labels = EXITS.map((p) => helpers.paneExitLabel({ ...p, at: 1 }));
+
+  it('produces the forms this test covers', () => {
+    expect(labels).toEqual(['exited', 'exited (0)', 'exited (3)', 'exited (137)', 'exited (-1)', 'exited (signal 9)']);
+  });
+
+  it('every badge form translates fully, and reads the same in English', () => {
+    const bad = labels.filter((l) => {
+      const text = zh.api.t(l);
+      return text === l || leftover(text).length > 0 || en.api.t(l) !== l;
+    });
+    expect(bad).toEqual([]);
+    expect(zh.api.t('exited (3)')).toBe('已退出（3）');
+    expect(zh.api.t('exited (signal 9)')).toBe('已退出（信号 9）');
+  });
+
+  it("the tab's accessible name translates around the session name, which stays as typed", () => {
+    for (const name of ['w1-case', 'Open tiles', 'Tiles']) {
+      for (const label of labels) {
+        const source = helpers.paneExitAriaLabel(name, label);
+        const text = zh.api.t(source);
+        expect(text.startsWith(`${name} 会话，智能体已退出`), `${source} -> ${text}`).toBe(true);
+        expect(leftover(text.slice(name.length))).toEqual([]);
+        expect(en.api.t(source)).toBe(source);
+      }
+    }
+  });
+});