feat(orchestrator): add MS23 per-agent message history and SSE stream endpoints

GET /agents/:id/messages - paginated message history
GET /agents/:id/messages/stream - SSE live stream with replay

Partial #693

apps/orchestrator/src/api/agents/agents.controller.ts

@@ -15,6 +15,7 @@ import {
   MessageEvent,
   Query,
 } from "@nestjs/common";
+import type { AgentConversationMessage } from "@prisma/client";
 import { Throttle } from "@nestjs/throttler";
 import { Observable } from "rxjs";
 import { QueueService } from "../../queue/queue.service";
@@ -25,6 +26,8 @@ import { SpawnAgentDto, SpawnAgentResponseDto } from "./dto/spawn-agent.dto";
 import { OrchestratorApiKeyGuard } from "../../common/guards/api-key.guard";
 import { OrchestratorThrottlerGuard } from "../../common/guards/throttler.guard";
 import { AgentEventsService } from "./agent-events.service";
+import { GetMessagesQueryDto } from "./dto/get-messages-query.dto";
+import { AgentMessagesService } from "./agent-messages.service";
 
 /**
  * Controller for agent management endpoints
@@ -47,7 +50,8 @@ export class AgentsController {
     private readonly spawnerService: AgentSpawnerService,
     private readonly lifecycleService: AgentLifecycleService,
     private readonly killswitchService: KillswitchService,
-    private readonly eventsService: AgentEventsService
+    private readonly eventsService: AgentEventsService,
+    private readonly messagesService: AgentMessagesService
   ) {}
 
   /**
@@ -185,6 +189,107 @@ export class AgentsController {
     }
   }
 
+  /**
+   * Get paginated message history for an agent.
+   */
+  @Get(":agentId/messages")
+  @Throttle({ status: { limit: 200, ttl: 60000 } })
+  @UsePipes(new ValidationPipe({ transform: true, whitelist: true }))
+  async getAgentMessages(
+    @Param("agentId", ParseUUIDPipe) agentId: string,
+    @Query() query: GetMessagesQueryDto
+  ): Promise<{
+    messages: AgentConversationMessage[];
+    total: number;
+  }> {
+    return this.messagesService.getMessages(agentId, query.limit, query.skip);
+  }
+
+  /**
+   * Stream per-agent conversation messages as server-sent events (SSE).
+   */
+  @Sse(":agentId/messages/stream")
+  @Throttle({ status: { limit: 200, ttl: 60000 } })
+  streamAgentMessages(@Param("agentId", ParseUUIDPipe) agentId: string): Observable<MessageEvent> {
+    return new Observable<MessageEvent>((subscriber) => {
+      let isClosed = false;
+      let lastSeenTimestamp = new Date();
+      let lastSeenMessageId: string | null = null;
+
+      const emitMessage = (message: AgentConversationMessage): void => {
+        if (isClosed) {
+          return;
+        }
+
+        subscriber.next({
+          data: this.toMessageStreamPayload(message),
+        });
+
+        lastSeenTimestamp = message.timestamp;
+        lastSeenMessageId = message.id;
+      };
+
+      void this.messagesService
+        .getReplayMessages(agentId, 50)
+        .then((messages) => {
+          if (isClosed) {
+            return;
+          }
+
+          messages.forEach((message) => {
+            emitMessage(message);
+          });
+
+          if (messages.length === 0) {
+            lastSeenTimestamp = new Date();
+            lastSeenMessageId = null;
+          }
+        })
+        .catch((error: unknown) => {
+          this.logger.error(
+            `Failed to load replay messages for ${agentId}: ${error instanceof Error ? error.message : String(error)}`
+          );
+          lastSeenTimestamp = new Date();
+          lastSeenMessageId = null;
+        });
+
+      const pollInterval = setInterval(() => {
+        if (isClosed) {
+          return;
+        }
+
+        void this.messagesService
+          .getMessagesAfter(agentId, lastSeenTimestamp, lastSeenMessageId)
+          .then((messages) => {
+            if (isClosed || messages.length === 0) {
+              return;
+            }
+
+            messages.forEach((message) => {
+              emitMessage(message);
+            });
+          })
+          .catch((error: unknown) => {
+            this.logger.error(
+              `Failed to poll messages for ${agentId}: ${error instanceof Error ? error.message : String(error)}`
+            );
+          });
+      }, 1000);
+
+      const heartbeat = setInterval(() => {
+        if (!isClosed) {
+          subscriber.next({ data: { type: "heartbeat" } });
+        }
+      }, 15000);
+
+      return () => {
+        isClosed = true;
+        clearInterval(pollInterval);
+        clearInterval(heartbeat);
+      };
+    });
+  }
+
   /**
    * Get agent status
    * @param agentId Agent ID to query
@@ -301,4 +406,24 @@ export class AgentsController {
       throw error;
     }
   }
+
+  private toMessageStreamPayload(message: AgentConversationMessage): {
+    messageId: string;
+    sessionId: string;
+    role: string;
+    content: string;
+    provider: string;
+    timestamp: string;
+    metadata: unknown;
+  } {
+    return {
+      messageId: message.id,
+      sessionId: message.sessionId,
+      role: message.role,
+      content: message.content,
+      provider: message.provider,
+      timestamp: message.timestamp.toISOString(),
+      metadata: message.metadata,
+    };
+  }
 }