Clear stale API-key credentials when a password session begins

Why: the auth middleware prefers Bearer keys over the session cookie, so a stale key left in localStorage shadows valid cookie sessions and every request after password login returns 401 (observed at http://192.168.3.2:8788 on 2026-10-11).
Evidence: modules/frontend vitest 19 files / 88 tests green; auth.test.ts covers beginSession clearing the stored Bearer before any fetch.
Impact: password logins switch to the HttpOnly cookie session cleanly; API-key logins unchanged.
Refs: task card feature-login-clear-stale-key in Agent-System-Dev.

src/auth.ts

@@ -22,6 +22,9 @@ export const auth = {
   apiKey(): string { return storage.getItem(KEY) ?? '' },
   setKey(key: string) { storage.setItem(KEY, key.trim()) },
   clear() { storage.removeItem(KEY) },
+  // 密码登录成功后切换到 HttpOnly 会话 cookie：必须清掉残留 Bearer——服务端
+  // 认证中间件 Bearer 优先于会话 cookie，失效残留 key 会把有效会话也判成 401。
+  beginSession() { this.clear() },
   // 带凭证的 fetch：未设置密钥时与原生 fetch 等价（嵌入式档无认证）。
   fetch(input: string, init?: RequestInit): Promise<Response> {
     const key = this.apiKey()

src/components/LoginPage.tsx

@@ -41,6 +41,8 @@ export function LoginPage({ onAuthed, onMustChange }: { onAuthed: () => void; on
     setErr(''); setBusy(true)
     try {
       const me = await api.login(owner.trim(), password)
+      // 会话凭证是 HttpOnly cookie；清残留 Bearer，避免其遮蔽有效会话。
+      auth.beginSession()
       if (me.mustChangePassword) {
         // 初始/重置密码：先完成强制改密再放行。
         onMustChange(me.owner)

test/auth.test.ts

@@ -40,4 +40,15 @@ describe('auth 凭证模块', () => {
     expect(auth.apiKey()).toBe('')
     expect(auth.withKey('/x')).toBe('/x')
   })
+
+  it('beginSession：密码会话生效后清残留 Bearer，fetch 不再带头', async () => {
+    auth.setKey('ask_stale')
+    auth.beginSession()
+    expect(auth.apiKey()).toBe('')
+    const spy = vi.fn().mockResolvedValue(new Response('{}'))
+    vi.stubGlobal('fetch', spy)
+    await auth.fetch('/api/me')
+    const [, init] = spy.mock.calls[0] as [string, RequestInit | undefined]
+    expect(new Headers(init?.headers ?? {}).get('Authorization')).toBeNull()
+  })
 })