feat(orchestrator): MS23 per-agent message history and SSE stream (#702)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/orchestrator/src/api/agents/agent-messages.service.ts

@@ -0,0 +1,84 @@
+import { Injectable } from "@nestjs/common";
+import { type AgentConversationMessage, type Prisma } from "@prisma/client";
+import { PrismaService } from "../../prisma/prisma.service";
+
+@Injectable()
+export class AgentMessagesService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async getMessages(
+    sessionId: string,
+    limit: number,
+    skip: number
+  ): Promise<{
+    messages: AgentConversationMessage[];
+    total: number;
+  }> {
+    const where = { sessionId };
+
+    const [messages, total] = await Promise.all([
+      this.prisma.agentConversationMessage.findMany({
+        where,
+        orderBy: {
+          timestamp: "desc",
+        },
+        take: limit,
+        skip,
+      }),
+      this.prisma.agentConversationMessage.count({ where }),
+    ]);
+
+    return {
+      messages,
+      total,
+    };
+  }
+
+  async getReplayMessages(sessionId: string, limit = 50): Promise<AgentConversationMessage[]> {
+    const messages = await this.prisma.agentConversationMessage.findMany({
+      where: { sessionId },
+      orderBy: {
+        timestamp: "desc",
+      },
+      take: limit,
+    });
+
+    return messages.reverse();
+  }
+
+  async getMessagesAfter(
+    sessionId: string,
+    lastSeenTimestamp: Date,
+    lastSeenMessageId: string | null
+  ): Promise<AgentConversationMessage[]> {
+    const where: Prisma.AgentConversationMessageWhereInput = {
+      sessionId,
+      ...(lastSeenMessageId
+        ? {
+            OR: [
+              {
+                timestamp: {
+                  gt: lastSeenTimestamp,
+                },
+              },
+              {
+                timestamp: lastSeenTimestamp,
+                id: {
+                  gt: lastSeenMessageId,
+                },
+              },
+            ],
+          }
+        : {
+            timestamp: {
+              gt: lastSeenTimestamp,
+            },
+          }),
+    };
+
+    return this.prisma.agentConversationMessage.findMany({
+      where,
+      orderBy: [{ timestamp: "asc" }, { id: "asc" }],
+    });
+  }
+}