Phase 2 scaffold: mitra online status & pairing logic

Add mitra online/offline status with heartbeat-based auto-offline,
customer-mitra pairing via Valkey pub/sub blast, session management,
and control center dashboard with real-time stats.

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

backend/src/services/mitra-status.service.js

@@ -0,0 +1,107 @@
+import { getDb } from '../db/client.js'
+
+const sql = getDb()
+
+export const ensureStatusRow = async (mitraId) => {
+  await sql`
+    INSERT INTO mitra_online_status (mitra_id)
+    VALUES (${mitraId})
+    ON CONFLICT (mitra_id) DO NOTHING
+  `
+}
+
+export const setOnline = async (mitraId) => {
+  await ensureStatusRow(mitraId)
+  const now = new Date()
+  await sql`
+    UPDATE mitra_online_status
+    SET is_online = true, last_online_at = ${now}, last_heartbeat_at = ${now}, updated_at = ${now}
+    WHERE mitra_id = ${mitraId}
+  `
+  await sql`
+    INSERT INTO mitra_online_logs (mitra_id, status) VALUES (${mitraId}, 'online')
+  `
+}
+
+export const setOffline = async (mitraId) => {
+  await ensureStatusRow(mitraId)
+  const now = new Date()
+  const [status] = await sql`
+    SELECT is_online FROM mitra_online_status WHERE mitra_id = ${mitraId}
+  `
+  if (!status?.is_online) return
+
+  await sql`
+    UPDATE mitra_online_status
+    SET is_online = false, last_offline_at = ${now}, updated_at = ${now}
+    WHERE mitra_id = ${mitraId}
+  `
+  await sql`
+    INSERT INTO mitra_online_logs (mitra_id, status) VALUES (${mitraId}, 'offline')
+  `
+}
+
+export const heartbeat = async (mitraId) => {
+  const now = new Date()
+  await sql`
+    UPDATE mitra_online_status
+    SET last_heartbeat_at = ${now}, updated_at = ${now}
+    WHERE mitra_id = ${mitraId} AND is_online = true
+  `
+}
+
+export const getStatus = async (mitraId) => {
+  await ensureStatusRow(mitraId)
+  const [status] = await sql`
+    SELECT is_online, last_online_at, last_offline_at, updated_at
+    FROM mitra_online_status
+    WHERE mitra_id = ${mitraId}
+  `
+  return status
+}
+
+export const getOnlineMitras = async () => {
+  const mitras = await sql`
+    SELECT m.id, m.display_name, m.phone, s.last_online_at, s.updated_at,
+      (SELECT COUNT(*) FROM chat_sessions cs
+       WHERE cs.mitra_id = m.id AND cs.status IN ('active', 'pending_payment')) AS active_session_count
+    FROM mitras m
+    INNER JOIN mitra_online_status s ON s.mitra_id = m.id
+    WHERE s.is_online = true AND m.is_active = true
+    ORDER BY s.last_online_at DESC
+  `
+  return mitras
+}
+
+export const getOnlineLogs = async (mitraId, { page = 1, limit = 50 } = {}) => {
+  const offset = (page - 1) * limit
+  const items = await sql`
+    SELECT id, status, timestamp
+    FROM mitra_online_logs
+    WHERE mitra_id = ${mitraId}
+    ORDER BY timestamp DESC
+    LIMIT ${limit} OFFSET ${offset}
+  `
+  const [{ count }] = await sql`
+    SELECT COUNT(*) FROM mitra_online_logs WHERE mitra_id = ${mitraId}
+  `
+  return { items, total: Number(count), page, limit }
+}
+
+export const autoOfflineStaleMitras = async (staleSeconds = 45) => {
+  const stale = await sql`
+    UPDATE mitra_online_status
+    SET is_online = false, last_offline_at = NOW(), updated_at = NOW()
+    WHERE is_online = true
+      AND last_heartbeat_at < NOW() - ${staleSeconds + ' seconds'}::interval
+    RETURNING mitra_id
+  `
+
+  for (const row of stale) {
+    await sql`
+      INSERT INTO mitra_online_logs (mitra_id, status) VALUES (${row.mitra_id}, 'offline')
+    `
+  }
+
+  return stale.length
+}