refactor(compute): gate ECS construct on compute_type context

Replace comment toggle with proper context gate. ECS resources only
synthesize when compute_type=ecs is passed. Default (agentcore) behavior
unchanged. Closes #164

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: scottschreckengaust

cdk/src/bootstrap/preflight/.gitkeep

@@ -23,8 +23,7 @@ import * as bedrock from '@aws-cdk/aws-bedrock-alpha';
 import * as agentcoremixins from '@aws-cdk/mixins-preview/aws-bedrockagentcore';
 import { ArnFormat, AspectPriority, Aspects, Stack, StackProps, RemovalPolicy, CfnOutput, CfnResource, Duration, Fn, Lazy } from 'aws-cdk-lib';
 import * as ec2 from 'aws-cdk-lib/aws-ec2';
-// ecr_assets import is only needed when the ECS block below is uncommented
-// import * as ecr_assets from 'aws-cdk-lib/aws-ecr-assets';
+import * as ecr_assets from 'aws-cdk-lib/aws-ecr-assets';
 import * as iam from 'aws-cdk-lib/aws-iam';
 import * as logs from 'aws-cdk-lib/aws-logs';
 import * as secretsmanager from 'aws-cdk-lib/aws-secretsmanager';
@@ -38,12 +37,12 @@ import { Blueprint } from '../constructs/blueprint';
 import { CedarWasmLayer } from '../constructs/cedar-wasm-layer';
 import { ConcurrencyReconciler } from '../constructs/concurrency-reconciler';
 import { DnsFirewall } from '../constructs/dns-firewall';
+import { EcsAgentCluster } from '../constructs/ecs-agent-cluster';
 import { FanOutConsumer } from '../constructs/fanout-consumer';
 import { LinearIntegration } from '../constructs/linear-integration';
 import { RepoTable } from '../constructs/repo-table';
 import { SlackIntegration } from '../constructs/slack-integration';
 import { StrandedTaskReconciler } from '../constructs/stranded-task-reconciler';
-// import { EcsAgentCluster } from '../constructs/ecs-agent-cluster';
 import { TaskApi } from '../constructs/task-api';
 import { TaskApprovalsTable } from '../constructs/task-approvals-table';
 import { TaskDashboard } from '../constructs/task-dashboard';
@@ -519,26 +518,25 @@ export class AgentStack extends Stack {
       description: 'Name of the S3 bucket storing --trace trajectory artifacts (design §10.1)',
     });
 
-    // --- ECS Fargate compute backend (optional) ---
-    // To enable ECS as an alternative compute backend, uncomment the block below
-    // and the EcsAgentCluster import at the top of this file. Repos can then use
-    // compute_type: 'ecs' in their blueprint config to route tasks to ECS Fargate.
-    //
-    // const agentImageAsset = new ecr_assets.DockerImageAsset(this, 'AgentImage', {
-    //   directory: repoRoot,
-    //   file: 'agent/Dockerfile',
-    //   platform: ecr_assets.Platform.LINUX_ARM64,
-    // });
-    //
-    // const ecsCluster = new EcsAgentCluster(this, 'EcsAgentCluster', {
-    //   vpc: agentVpc.vpc,
-    //   agentImageAsset,
-    //   taskTable: taskTable.table,
-    //   taskEventsTable: taskEventsTable.table,
-    //   userConcurrencyTable: userConcurrencyTable.table,
-    //   githubTokenSecret,
-    //   memoryId: agentMemory.memory.memoryId,
-    // });
+    // --- ECS Fargate compute backend (enabled when compute_type=ecs) ---
+    const computeType = this.node.tryGetContext('compute_type') ?? 'agentcore';
+    if (computeType === 'ecs') {
+      const agentImageAsset = new ecr_assets.DockerImageAsset(this, 'AgentImage', {
+        directory: repoRoot,
+        file: 'agent/Dockerfile',
+        platform: ecr_assets.Platform.LINUX_ARM64,
+      });
+
+      new EcsAgentCluster(this, 'EcsAgentCluster', {
+        vpc: agentVpc.vpc,
+        agentImageAsset,
+        taskTable: taskTable.table,
+        taskEventsTable: taskEventsTable.table,
+        userConcurrencyTable: userConcurrencyTable.table,
+        githubTokenSecret,
+        memoryId: agentMemory.memory.memoryId,
+      });
+    }
 
     // --- Task Orchestrator (durable Lambda function) ---
     const orchestrator = new TaskOrchestrator(this, 'TaskOrchestrator', {