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/pairing.service.js

@@ -1,6 +1,8 @@
 import { getDb } from '../db/client.js'
 import { getMaxCustomersPerMitra } from './config.service.js'
 import { publish } from '../plugins/valkey.js'
+import { startSessionTimer } from './session-timer.service.js'
+import { startSessionListener } from './chat-handler.service.js'
 
 const sql = getDb()
 
@@ -23,7 +25,7 @@ export const findAvailableMitras = async () => {
   return mitras
 }
 
-export const createPairingRequest = async (customerId) => {
+export const createPairingRequest = async (customerId, { duration_minutes, price, is_free_trial } = {}) => {
   // Check for existing active session or request
   const [existing] = await sql`
     SELECT id, status FROM chat_sessions
@@ -43,11 +45,11 @@ export const createPairingRequest = async (customerId) => {
     })
   }
 
-  // Create session
+  // Create session with duration/price
   const [session] = await sql`
-    INSERT INTO chat_sessions (customer_id, status)
-    VALUES (${customerId}, 'pending_acceptance')
-    RETURNING id, customer_id, status, created_at
+    INSERT INTO chat_sessions (customer_id, status, duration_minutes, price, is_free_trial)
+    VALUES (${customerId}, 'pending_acceptance', ${duration_minutes || null}, ${price || 0}, ${is_free_trial || false})
+    RETURNING id, customer_id, status, duration_minutes, price, is_free_trial, created_at
   `
 
   // Create notifications for all available mitras
@@ -111,13 +113,35 @@ export const acceptPairingRequest = async (sessionId, mitraId) => {
     pairingTimeouts.delete(sessionId)
   }
 
-  // Auto-skip payment for now: move to active
+  // Auto-skip payment for now: move to active and set expires_at
   const [activeSession] = await sql`
-    UPDATE chat_sessions SET status = 'active'
+    UPDATE chat_sessions
+    SET status = 'active',
+        expires_at = CASE
+          WHEN duration_minutes IS NOT NULL THEN NOW() + (duration_minutes || ' minutes')::interval
+          ELSE NULL
+        END
     WHERE id = ${sessionId}
-    RETURNING id, customer_id, mitra_id, status, paired_at
+    RETURNING id, customer_id, mitra_id, status, paired_at, duration_minutes, price, is_free_trial, expires_at
   `
 
+  // Record transaction
+  if (activeSession.duration_minutes) {
+    const txType = activeSession.is_free_trial ? 'free_trial' : 'paid'
+    await sql`
+      INSERT INTO customer_transactions (customer_id, session_id, type, amount)
+      VALUES (${activeSession.customer_id}, ${sessionId}, ${txType}, ${activeSession.price || 0})
+    `
+  }
+
+  // Start session timer if duration is set
+  if (activeSession.expires_at) {
+    startSessionTimer(sessionId, activeSession.expires_at)
+  }
+
+  // Start chat message listener for this session
+  startSessionListener(sessionId)
+
   // Get mitra display name for customer notification
   const [mitra] = await sql`
     SELECT display_name FROM mitras WHERE id = ${mitraId}