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/session-timer.service.js

@@ -0,0 +1,100 @@
+import { getDb } from '../db/client.js'
+import { publish } from '../plugins/valkey.js'
+import { sendToSessionParticipant } from '../plugins/websocket.js'
+
+const sql = getDb()
+
+// Active session timers: sessionId → { warningTimeout, expiryTimeout }
+const sessionTimers = new Map()
+
+export const startSessionTimer = (sessionId, expiresAt) => {
+  const now = Date.now()
+  const expiresMs = new Date(expiresAt).getTime()
+  const warningMs = expiresMs - 60_000 // 1 minute before expiry
+
+  // Clear any existing timers
+  clearSessionTimer(sessionId)
+
+  const timers = {}
+
+  // Warning timer (1 min before expiry)
+  if (warningMs > now) {
+    timers.warningTimeout = setTimeout(() => {
+      onSessionWarning(sessionId)
+    }, warningMs - now)
+  }
+
+  // Expiry timer
+  if (expiresMs > now) {
+    timers.expiryTimeout = setTimeout(() => {
+      onSessionExpired(sessionId)
+    }, expiresMs - now)
+  } else {
+    // Already expired
+    onSessionExpired(sessionId)
+    return
+  }
+
+  sessionTimers.set(sessionId, timers)
+}
+
+export const clearSessionTimer = (sessionId) => {
+  const timers = sessionTimers.get(sessionId)
+  if (timers) {
+    if (timers.warningTimeout) clearTimeout(timers.warningTimeout)
+    if (timers.expiryTimeout) clearTimeout(timers.expiryTimeout)
+    sessionTimers.delete(sessionId)
+  }
+}
+
+export const extendSessionTimer = async (sessionId, additionalMinutes) => {
+  const [session] = await sql`
+    UPDATE chat_sessions
+    SET expires_at = expires_at + ${additionalMinutes + ' minutes'}::interval,
+        extended_minutes = extended_minutes + ${additionalMinutes}
+    WHERE id = ${sessionId}
+    RETURNING id, expires_at
+  `
+  if (session) {
+    startSessionTimer(sessionId, session.expires_at)
+  }
+  return session
+}
+
+const onSessionWarning = (sessionId) => {
+  const data = { type: 'session_timer', remaining_seconds: 60, session_id: sessionId }
+  sendToSessionParticipant(sessionId, 'customer', data)
+  sendToSessionParticipant(sessionId, 'mitra', data)
+}
+
+const onSessionExpired = async (sessionId) => {
+  clearSessionTimer(sessionId)
+
+  // Check session is still active
+  const [session] = await sql`
+    SELECT id, status FROM chat_sessions WHERE id = ${sessionId} AND status = 'active'
+  `
+  if (!session) return
+
+  // Notify both parties
+  const data = { type: 'session_expired', session_id: sessionId }
+  sendToSessionParticipant(sessionId, 'customer', data)
+  sendToSessionParticipant(sessionId, 'mitra', data)
+
+  // Also publish via Valkey for any listeners
+  await publish(`session:${sessionId}:status`, data)
+}
+
+// Restore timers for active sessions on server restart
+export const restoreActiveTimers = async () => {
+  const activeSessions = await sql`
+    SELECT id, expires_at FROM chat_sessions
+    WHERE status = 'active' AND expires_at IS NOT NULL AND expires_at > NOW()
+  `
+  for (const session of activeSessions) {
+    startSessionTimer(session.id, session.expires_at)
+  }
+  if (activeSessions.length > 0) {
+    console.log(`Restored ${activeSessions.length} session timer(s)`)
+  }
+}