feat(23-01): extend chat service with messageType support and addSystemMessage

- addMessage now accepts optional messageType parameter
- addSystemMessage helper inserts system-role messages with typed messageType
- Both methods bump conversation updatedAt for correct sort order

server/src/services/chat.ts

@@ -137,7 +137,7 @@ export function chatService(db: Db) {
 
     async addMessage(
       conversationId: string,
-      data: { role: string; content: string; agentId?: string },
+      data: { role: string; content: string; agentId?: string; messageType?: string },
     ) {
       const [message] = await db
         .insert(chatMessages)
@@ -146,6 +146,7 @@ export function chatService(db: Db) {
           role: data.role,
           content: data.content,
           agentId: data.agentId ?? null,
+          messageType: data.messageType ?? null,
         })
         .returning();
 
@@ -192,6 +193,30 @@ export function chatService(db: Db) {
         );
     },
 
+    async addSystemMessage(
+      conversationId: string,
+      data: { content: string; messageType: string; agentId?: string },
+    ) {
+      const [message] = await db
+        .insert(chatMessages)
+        .values({
+          conversationId,
+          role: "system",
+          content: data.content,
+          agentId: data.agentId ?? null,
+          messageType: data.messageType,
+        })
+        .returning();
+
+      // Bump conversation updatedAt (same pattern as addMessage)
+      await db
+        .update(chatConversations)
+        .set({ updatedAt: new Date() })
+        .where(eq(chatConversations.id, conversationId));
+
+      return message!;
+    },
+
     async *streamEcho(content: string, signal: AbortSignal) {
       const words = content.split(/\s+/);
       for (const word of words) {