fix: track live downstream cmpp connections

api/prisma/schema.prisma

@@ -40,6 +40,7 @@ model Tenant {
   smsUplinkMessages     SmsUplinkMessage[]
   smsUplinkMatchCandidates SmsUplinkMatchCandidate[]
   cmppDownstreamDeliveries CmppDownstreamDelivery[]
+  cmppDownstreamConnections CmppDownstreamConnection[]
   cmppConnectionStates  CmppConnectionState[]
   gatewayDownstreamRecoveryStatuses GatewayDownstreamRecoveryStatus[]
   gatewaySubmitDeadLetters GatewaySubmitDeadLetter[]
@@ -371,6 +372,7 @@ model SmsApplication {
   uplinkMessages SmsUplinkMessage[]
   uplinkMatchCandidates SmsUplinkMatchCandidate[]
   downstreamDeliveries CmppDownstreamDelivery[]
+  downstreamConnections CmppDownstreamConnection[]
   connectionStates CmppConnectionState[]
   gatewayDownstreamRecoveryStatuses GatewayDownstreamRecoveryStatus[]
   gatewaySubmitDeadLetters GatewaySubmitDeadLetter[]
@@ -550,6 +552,33 @@ model CmppConnectionState {
   @@index([channelId, status])
 }
 
+model CmppDownstreamConnection {
+  id                 String   @id @default(cuid())
+  tenantId           String
+  applicationId      String
+  account            String
+  enterpriseCode     String
+  connectionId       String   @unique
+  remoteIp           String?
+  protocol           String?
+  status             String   @default("connected")
+  connectedAt        DateTime @default(now())
+  lastHeartbeatAt    DateTime?
+  lastSubmitAt       DateTime?
+  lastDeliverAt      DateTime?
+  disconnectedAt     DateTime?
+  lastError          String?
+  createdAt          DateTime @default(now())
+  updatedAt          DateTime @updatedAt
+
+  tenant      Tenant         @relation(fields: [tenantId], references: [id])
+  application SmsApplication @relation(fields: [applicationId], references: [id])
+
+  @@index([applicationId, status, updatedAt])
+  @@index([tenantId, status, updatedAt])
+  @@index([account, status])
+}
+
 model SmsChannelGroup {
   id          String   @id @default(cuid())
   code        String   @unique