feat(chat): 访客与客服聊天界面、历史拉取与断线重连

聊天页支持发送确认、历史补拉和重连；刷新后不重复展示已确认消息。

frontend/src/__tests__/utils/widgetPresence.spec.ts

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+/*
+Copyright 2024-2026 ReplyPier
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { describe, expect, it } from 'vitest'
+import { presenceLine } from '@/utils/widgetPresence'
+
+describe('presenceLine', () => {
+  it('promises instant replies only while the AI is answering', () => {
+    const line = presenceLine({ mode: 'ai', available: true })
+    expect(line).toEqual({ text: '在线 · 立即回复', online: true })
+  })
+
+  it('ignores business hours for an AI agent — it answers at 3am too', () => {
+    expect(presenceLine({ mode: 'ai', available: false }).online).toBe(true)
+  })
+
+  it('sets a softer expectation when a person has to reply', () => {
+    const line = presenceLine({ mode: 'human', available: true })
+    expect(line.text).toBe('在线 · 通常几分钟内回复')
+    expect(line.online).toBe(true)
+  })
+
+  it('says away outside business hours instead of claiming to be online', () => {
+    const line = presenceLine({ mode: 'human', available: false })
+    expect(line.text).toContain('离开')
+    expect(line.online).toBe(false)
+  })
+
+  it('switches to the human wording once someone takes the chat over', () => {
+    // The agent still has AI enabled, but a person owns this conversation now.
+    expect(presenceLine({ mode: 'ai', available: true }, true).text).toBe(
+      '在线 · 通常几分钟内回复'
+    )
+    expect(presenceLine({ mode: 'ai', available: false }, true).online).toBe(false)
+  })
+
+  it('keeps the old wording when the payload predates presence', () => {
+    // An older cached widget page sends nothing — do not declare the team away
+    // on no evidence.
+    expect(presenceLine(undefined).text).toBe('在线 · 立即回复')
+    expect(presenceLine({}).text).toBe('在线 · 立即回复')
+  })
+})