fix(#338): Add max concurrent agents limit

- Add MAX_CONCURRENT_AGENTS configuration (default: 20)
- Check current agent count before spawning
- Reject spawn requests with 429 Too Many Requests when limit reached
- Add comprehensive tests for limit enforcement

Refs #338

apps/orchestrator/src/spawner/agent-spawner.service.ts

@@ -1,4 +1,4 @@
-import { Injectable, Logger } from "@nestjs/common";
+import { Injectable, Logger, HttpException, HttpStatus } from "@nestjs/common";
 import { ConfigService } from "@nestjs/config";
 import Anthropic from "@anthropic-ai/sdk";
 import { randomUUID } from "crypto";
@@ -17,6 +17,7 @@ export class AgentSpawnerService {
   private readonly logger = new Logger(AgentSpawnerService.name);
   private readonly anthropic: Anthropic;
   private readonly sessions = new Map<string, AgentSession>();
+  private readonly maxConcurrentAgents: number;
 
   constructor(private readonly configService: ConfigService) {
     const apiKey = this.configService.get<string>("orchestrator.claude.apiKey");
@@ -29,7 +30,13 @@ export class AgentSpawnerService {
       apiKey,
     });
 
-    this.logger.log("AgentSpawnerService initialized with Claude SDK");
+    // Default to 20 if not configured
+    this.maxConcurrentAgents =
+      this.configService.get<number>("orchestrator.spawner.maxConcurrentAgents") ?? 20;
+
+    this.logger.log(
+      `AgentSpawnerService initialized with Claude SDK (max concurrent agents: ${String(this.maxConcurrentAgents)})`
+    );
   }
 
   /**
@@ -40,6 +47,9 @@ export class AgentSpawnerService {
   spawnAgent(request: SpawnAgentRequest): SpawnAgentResponse {
     this.logger.log(`Spawning agent for task: ${request.taskId}`);
 
+    // Check concurrent agent limit before proceeding
+    this.checkConcurrentAgentLimit();
+
     // Validate request
     this.validateSpawnRequest(request);
 
@@ -90,6 +100,27 @@ export class AgentSpawnerService {
     return Array.from(this.sessions.values());
   }
 
+  /**
+   * Check if the concurrent agent limit has been reached
+   * @throws HttpException with 429 Too Many Requests if limit reached
+   */
+  private checkConcurrentAgentLimit(): void {
+    const currentCount = this.sessions.size;
+    if (currentCount >= this.maxConcurrentAgents) {
+      this.logger.warn(
+        `Maximum concurrent agents limit reached: ${String(currentCount)}/${String(this.maxConcurrentAgents)}`
+      );
+      throw new HttpException(
+        {
+          message: `Maximum concurrent agents limit reached (${String(this.maxConcurrentAgents)}). Please wait for existing agents to complete.`,
+          currentCount,
+          maxLimit: this.maxConcurrentAgents,
+        },
+        HttpStatus.TOO_MANY_REQUESTS
+      );
+    }
+  }
+
   /**
    * Validate spawn agent request
    * @param request Spawn request to validate