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/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" }],
+    });
+  }
+}

apps/orchestrator/src/api/agents/agents-killswitch.controller.spec.ts

@@ -5,6 +5,7 @@ import { AgentSpawnerService } from "../../spawner/agent-spawner.service";
 import { AgentLifecycleService } from "../../spawner/agent-lifecycle.service";
 import { KillswitchService } from "../../killswitch/killswitch.service";
 import { AgentEventsService } from "./agent-events.service";
+import { AgentMessagesService } from "./agent-messages.service";
 import type { KillAllResult } from "../../killswitch/killswitch.service";
 
 describe("AgentsController - Killswitch Endpoints", () => {
@@ -27,6 +28,12 @@ describe("AgentsController - Killswitch Endpoints", () => {
     subscribe: ReturnType<typeof vi.fn>;
     getInitialSnapshot: ReturnType<typeof vi.fn>;
     createHeartbeat: ReturnType<typeof vi.fn>;
+    getRecentEvents: ReturnType<typeof vi.fn>;
+  };
+  let mockMessagesService: {
+    getMessages: ReturnType<typeof vi.fn>;
+    getReplayMessages: ReturnType<typeof vi.fn>;
+    getMessagesAfter: ReturnType<typeof vi.fn>;
   };
 
   beforeEach(() => {
@@ -61,6 +68,13 @@ describe("AgentsController - Killswitch Endpoints", () => {
         timestamp: new Date().toISOString(),
         data: { heartbeat: true },
       }),
+      getRecentEvents: vi.fn().mockReturnValue([]),
+    };
+
+    mockMessagesService = {
+      getMessages: vi.fn(),
+      getReplayMessages: vi.fn().mockResolvedValue([]),
+      getMessagesAfter: vi.fn().mockResolvedValue([]),
     };
 
     controller = new AgentsController(
@@ -68,7 +82,8 @@ describe("AgentsController - Killswitch Endpoints", () => {
       mockSpawnerService as unknown as AgentSpawnerService,
       mockLifecycleService as unknown as AgentLifecycleService,
       mockKillswitchService as unknown as KillswitchService,
-      mockEventsService as unknown as AgentEventsService
+      mockEventsService as unknown as AgentEventsService,
+      mockMessagesService as unknown as AgentMessagesService
     );
   });
 

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

@@ -4,6 +4,7 @@ import { AgentSpawnerService } from "../../spawner/agent-spawner.service";
 import { AgentLifecycleService } from "../../spawner/agent-lifecycle.service";
 import { KillswitchService } from "../../killswitch/killswitch.service";
 import { AgentEventsService } from "./agent-events.service";
+import { AgentMessagesService } from "./agent-messages.service";
 import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 
 describe("AgentsController", () => {
@@ -30,6 +31,11 @@ describe("AgentsController", () => {
     createHeartbeat: ReturnType<typeof vi.fn>;
     getRecentEvents: ReturnType<typeof vi.fn>;
   };
+  let messagesService: {
+    getMessages: ReturnType<typeof vi.fn>;
+    getReplayMessages: ReturnType<typeof vi.fn>;
+    getMessagesAfter: ReturnType<typeof vi.fn>;
+  };
 
   beforeEach(() => {
     // Create mock services
@@ -69,13 +75,20 @@ describe("AgentsController", () => {
       getRecentEvents: vi.fn().mockReturnValue([]),
     };
 
+    messagesService = {
+      getMessages: vi.fn(),
+      getReplayMessages: vi.fn().mockResolvedValue([]),
+      getMessagesAfter: vi.fn().mockResolvedValue([]),
+    };
+
     // Create controller with mocked services
     controller = new AgentsController(
       queueService as unknown as QueueService,
       spawnerService as unknown as AgentSpawnerService,
       lifecycleService as unknown as AgentLifecycleService,
       killswitchService as unknown as KillswitchService,
-      eventsService as unknown as AgentEventsService
+      eventsService as unknown as AgentEventsService,
+      messagesService as unknown as AgentMessagesService
     );
   });
 
@@ -365,6 +378,52 @@ describe("AgentsController", () => {
     });
   });
 
+  describe("getAgentMessages", () => {
+    it("should return paginated message history", async () => {
+      const agentId = "0b64079f-4487-42b9-92eb-cf8ea0042a64";
+      const query = {
+        limit: 25,
+        skip: 10,
+      };
+
+      const response = {
+        messages: [
+          {
+            id: "msg-1",
+            sessionId: agentId,
+            role: "agent",
+            content: "hello",
+            provider: "internal",
+            timestamp: new Date("2026-03-07T03:00:00.000Z"),
+            metadata: {},
+          },
+        ],
+        total: 101,
+      };
+
+      messagesService.getMessages.mockResolvedValue(response);
+
+      const result = await controller.getAgentMessages(agentId, query);
+
+      expect(messagesService.getMessages).toHaveBeenCalledWith(agentId, 25, 10);
+      expect(result).toEqual(response);
+    });
+
+    it("should use default pagination values", async () => {
+      const agentId = "0b64079f-4487-42b9-92eb-cf8ea0042a64";
+      const query = {
+        limit: 50,
+        skip: 0,
+      };
+
+      messagesService.getMessages.mockResolvedValue({ messages: [], total: 0 });
+
+      await controller.getAgentMessages(agentId, query);
+
+      expect(messagesService.getMessages).toHaveBeenCalledWith(agentId, 50, 0);
+    });
+  });
+
   describe("getRecentEvents", () => {
     it("should return recent events with default limit", () => {
       eventsService.getRecentEvents.mockReturnValue([

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,
+    };
+  }
 }

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

@@ -6,10 +6,12 @@ import { KillswitchModule } from "../../killswitch/killswitch.module";
 import { ValkeyModule } from "../../valkey/valkey.module";
 import { OrchestratorApiKeyGuard } from "../../common/guards/api-key.guard";
 import { AgentEventsService } from "./agent-events.service";
+import { PrismaModule } from "../../prisma/prisma.module";
+import { AgentMessagesService } from "./agent-messages.service";
 
 @Module({
-  imports: [QueueModule, SpawnerModule, KillswitchModule, ValkeyModule],
+  imports: [QueueModule, SpawnerModule, KillswitchModule, ValkeyModule, PrismaModule],
   controllers: [AgentsController],
-  providers: [OrchestratorApiKeyGuard, AgentEventsService],
+  providers: [OrchestratorApiKeyGuard, AgentEventsService, AgentMessagesService],
 })
 export class AgentsModule {}

apps/orchestrator/src/api/agents/dto/get-messages-query.dto.spec.ts

@@ -0,0 +1,37 @@
+import { plainToInstance } from "class-transformer";
+import { validate } from "class-validator";
+import { describe, expect, it } from "vitest";
+import { GetMessagesQueryDto } from "./get-messages-query.dto";
+
+describe("GetMessagesQueryDto", () => {
+  it("should use defaults when empty", async () => {
+    const dto = plainToInstance(GetMessagesQueryDto, {});
+    const errors = await validate(dto);
+
+    expect(errors).toHaveLength(0);
+    expect(dto.limit).toBe(50);
+    expect(dto.skip).toBe(0);
+  });
+
+  it("should reject limit greater than 200", async () => {
+    const dto = plainToInstance(GetMessagesQueryDto, {
+      limit: 201,
+      skip: 0,
+    });
+    const errors = await validate(dto);
+
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors.some((error) => error.property === "limit")).toBe(true);
+  });
+
+  it("should reject negative skip", async () => {
+    const dto = plainToInstance(GetMessagesQueryDto, {
+      limit: 50,
+      skip: -1,
+    });
+    const errors = await validate(dto);
+
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors.some((error) => error.property === "skip")).toBe(true);
+  });
+});

apps/orchestrator/src/api/agents/dto/get-messages-query.dto.ts

@@ -0,0 +1,17 @@
+import { Type } from "class-transformer";
+import { IsInt, IsOptional, Max, Min } from "class-validator";
+
+export class GetMessagesQueryDto {
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  @Max(200)
+  limit = 50;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  @Min(0)
+  skip = 0;
+}