diff --git a/src/chat-core/types/message.ts b/src/chat-core/types/message.ts
index 66a6569a..8f1e3da8 100644
--- a/src/chat-core/types/message.ts
+++ b/src/chat-core/types/message.ts
@@ -7,7 +7,19 @@ export type MessageDirection = 'INBOUND' | 'OUTBOUND';
 
 export type MessageType = 'TEXT' | 'IMAGE' | 'VIDEO' | 'SYSTEM' | 'UNKNOWN';
 
-export type MessageActorType = 'MEDIA_USER' | 'MEDIA_ACCOUNT' | 'SYSTEM';
+/**
+ * Message sender type — polymorphic discriminator for (senderType, senderId).
+ * INBOUND → MEDIA_USER, OUTBOUND → MEDIA_ACCOUNT, SYSTEM → SYSTEM (id is null).
+ * Agent never appears here; the operator is tracked via operatorAgentId.
+ */
+export type MessageSenderType = 'MEDIA_USER' | 'MEDIA_ACCOUNT' | 'SYSTEM';
+
+/**
+ * Message receiver type — polymorphic discriminator for (receiverType, receiverId).
+ * Mirror of sender side: INBOUND → MEDIA_ACCOUNT, OUTBOUND → MEDIA_USER,
+ * SYSTEM → SYSTEM (id is null).
+ */
+export type MessageReceiverType = 'MEDIA_USER' | 'MEDIA_ACCOUNT' | 'SYSTEM';
 
 export type SendStatus = 'PENDING' | 'SENDING' | 'SENT' | 'FAILED' | 'STUCK';
 
@@ -42,12 +54,12 @@ export interface Message {
   direction: MessageDirection;
   msgType: MessageType;
 
-  senderType: MessageActorType;
+  senderType: MessageSenderType;
   senderId?: number;
   senderExternalId?: string;
   sender?: MessageActorRef;
 
-  receiverType: MessageActorType;
+  receiverType: MessageReceiverType;
   receiverId?: number;
   receiverExternalId?: string;
   receiver?: MessageActorRef;