Phase 3 scaffold: chat engine (WebSocket, FCM, pricing, timer, extension, history)

- Backend: WebSocket plugin, chat/pricing/timer/extension/closure/notification services
- Client app: ChatBloc, pricing dialog, chat screen with message status, extension/goodbye flow, history
- Mitra app: MitraChatBloc, ExtensionBloc, chat screen, extension accept/reject, history
- Control center: free trial, extension timeout, early end config toggles
- DB migration: chat_messages, session_closures, session_extensions, customer_transactions tables

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/services/extension.service.js

@@ -0,0 +1,159 @@
+import { getDb } from '../db/client.js'
+import { publish } from '../plugins/valkey.js'
+import { sendToSessionParticipant } from '../plugins/websocket.js'
+import { extendSessionTimer } from './session-timer.service.js'
+
+const sql = getDb()
+
+// Extension timeout map: extensionId → timeoutId
+const extensionTimeouts = new Map()
+
+const getExtensionTimeout = async () => {
+  const [row] = await sql`SELECT value FROM app_config WHERE key = 'extension_timeout_seconds'`
+  return (row?.value?.value ?? 60) * 1000 // Convert to ms
+}
+
+export const requestExtension = async (sessionId, customerId, { duration_minutes, price }) => {
+  // Verify session belongs to customer and just expired
+  const [session] = await sql`
+    SELECT id, customer_id, mitra_id, status FROM chat_sessions
+    WHERE id = ${sessionId} AND customer_id = ${customerId}
+  `
+  if (!session) {
+    throw Object.assign(new Error('Session not found'), { code: 'NOT_FOUND', statusCode: 404 })
+  }
+
+  // Create extension record
+  const [extension] = await sql`
+    INSERT INTO session_extensions (session_id, requested_duration_minutes, requested_price, status)
+    VALUES (${sessionId}, ${duration_minutes}, ${price}, 'pending')
+    RETURNING id, session_id, requested_duration_minutes, requested_price, status, requested_at
+  `
+
+  // Pause the session
+  await sql`UPDATE chat_sessions SET status = 'extending' WHERE id = ${sessionId}`
+
+  // Notify mitra
+  sendToSessionParticipant(sessionId, 'mitra', {
+    type: 'extension_request',
+    extension_id: extension.id,
+    session_id: sessionId,
+    duration_minutes,
+    price,
+  })
+
+  // Notify customer that chat is paused
+  sendToSessionParticipant(sessionId, 'customer', {
+    type: 'session_paused',
+    session_id: sessionId,
+    reason: 'extension_pending',
+  })
+
+  // Start timeout
+  const timeoutMs = await getExtensionTimeout()
+  const timeoutId = setTimeout(async () => {
+    try {
+      await timeoutExtension(extension.id, sessionId)
+    } catch (_) {}
+  }, timeoutMs)
+  extensionTimeouts.set(extension.id, timeoutId)
+
+  return extension
+}
+
+export const respondToExtension = async (extensionId, sessionId, mitraId, accepted) => {
+  const status = accepted ? 'accepted' : 'rejected'
+
+  const [extension] = await sql`
+    UPDATE session_extensions
+    SET status = ${status}, responded_at = NOW()
+    WHERE id = ${extensionId} AND status = 'pending'
+    RETURNING id, session_id, requested_duration_minutes, requested_price, status
+  `
+
+  if (!extension) {
+    throw Object.assign(new Error('Extension not found or already resolved'), {
+      code: 'EXTENSION_RESOLVED', statusCode: 409,
+    })
+  }
+
+  // Clear timeout
+  const timeoutId = extensionTimeouts.get(extensionId)
+  if (timeoutId) {
+    clearTimeout(timeoutId)
+    extensionTimeouts.delete(extensionId)
+  }
+
+  if (accepted) {
+    // Extend the session
+    await extendSessionTimer(extension.session_id, extension.requested_duration_minutes)
+
+    // Resume session
+    await sql`UPDATE chat_sessions SET status = 'active' WHERE id = ${extension.session_id}`
+
+    // Record transaction
+    await sql`
+      INSERT INTO customer_transactions (customer_id, session_id, type, amount)
+      SELECT customer_id, id, 'extension', ${extension.requested_price}
+      FROM chat_sessions WHERE id = ${extension.session_id}
+    `
+
+    // Notify both parties
+    sendToSessionParticipant(sessionId, 'customer', {
+      type: 'extension_response',
+      accepted: true,
+      duration_minutes: extension.requested_duration_minutes,
+    })
+    sendToSessionParticipant(sessionId, 'mitra', {
+      type: 'session_resumed',
+      session_id: sessionId,
+    })
+  } else {
+    // Rejected — proceed to closure
+    await sql`UPDATE chat_sessions SET status = 'closing' WHERE id = ${extension.session_id}`
+
+    sendToSessionParticipant(sessionId, 'customer', {
+      type: 'extension_response',
+      accepted: false,
+    })
+    sendToSessionParticipant(sessionId, 'mitra', {
+      type: 'session_closing',
+      session_id: sessionId,
+    })
+    sendToSessionParticipant(sessionId, 'customer', {
+      type: 'session_closing',
+      session_id: sessionId,
+    })
+  }
+
+  return extension
+}
+
+const timeoutExtension = async (extensionId, sessionId) => {
+  extensionTimeouts.delete(extensionId)
+
+  const [extension] = await sql`
+    UPDATE session_extensions
+    SET status = 'timeout', responded_at = NOW()
+    WHERE id = ${extensionId} AND status = 'pending'
+    RETURNING id, session_id
+  `
+  if (!extension) return
+
+  // Timeout = proceed to closure
+  await sql`UPDATE chat_sessions SET status = 'closing' WHERE id = ${extension.session_id}`
+
+  sendToSessionParticipant(sessionId, 'customer', {
+    type: 'extension_response',
+    accepted: false,
+    reason: 'timeout',
+  })
+  sendToSessionParticipant(sessionId, 'mitra', {
+    type: 'session_closing',
+    session_id: sessionId,
+  })
+  sendToSessionParticipant(sessionId, 'customer', {
+    type: 'session_closing',
+    session_id: sessionId,
+  })
+}