docs: 交付文档、维护指引与端到端回归

补齐 README、开发计划、维护交接与 E2E 用例，执行最终验收。

e2e/specs/channels/replies.spec.ts

@@ -0,0 +1,19 @@
+import { test, expect, channels, expectUnchanged, AI_REPLY } from '@e2e'
+
+// The core promise of every channel: a customer writes in, the agent's answer goes
+// back out on the same channel, to that customer.
+for (const [name, connect] of Object.entries(channels)) {
+  test(`a customer on ${name} gets the agent's answer back there @channels`, async ({ agent, llm, adminApi, request }) => {
+    await llm.script(agent, (s) => s
+      .when(/opening hours/i).reply('We are open 9am to 5pm, Monday to Friday.')
+      .otherwise().reply('Happy to help!'))
+
+    const channel = await connect({ api: adminApi, request, agentId: agent.id })
+    const chat = channel.chatWith('Tess')
+    await chat.send('What are your opening hours?')
+
+    // Exactly one answer, the scripted one, from this account — no duplicate, no default.
+    await expect.poll(() => chat.replies(), AI_REPLY).toEqual(['We are open 9am to 5pm, Monday to Friday.'])
+    await expectUnchanged(`${name} replies`, () => chat.replies())
+  })
+}