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/retries.spec.ts

@@ -0,0 +1,23 @@
+import { test, expect, connectWhatsAppNumber, deliverMeta, expectUnchanged, phoneNumber, routeToAgent, whatsappPayload, FakeExternals, AI_REPLY } from '@e2e'
+
+// Providers retry a webhook they think failed. Dedupe lives in Redis, which only
+// the nightly Redis run turns on (scripts/stack.sh E2E_REDIS_URL); playwright.config.ts
+// leaves @redis tests out otherwise.
+
+test('a provider delivering the same message twice gets one answer @channels @redis', async ({ agent, llm, adminApi, request }) => {
+  await llm.script(agent, (s) => s.otherwise().reply('Answered once.'))
+  const number = await connectWhatsAppNumber(adminApi)
+  await routeToAgent(adminApi, number.account.id, agent.id)
+  const waId = phoneNumber().slice(1)
+
+  // The exact same delivery, message id included, twice.
+  const payload = whatsappPayload(number.phoneNumberId, waId, 'Rita', { type: 'text', text: { body: 'Hello?' } })
+  await deliverMeta(request, payload)
+  await deliverMeta(request, payload)
+
+  const sent = async () => (await new FakeExternals(request).calls('graph', 'messages', { contains: waId }))
+    .filter((c) => (c.body as { type?: string }).type === 'text').length
+  await expect.poll(sent, AI_REPLY).toBe(1)
+  await expectUnchanged('replies to the retried message', sent)
+  expect(await llm.requests(agent)).toHaveLength(1)
+})