Step Functions Multi-Agent: Multi-Agent Coding Pipelines With Human Approval Gates

{
  "Comment": "Multi-agent coding pipeline",
  "StartAt": "PlanAgent",
  "States": {
    "PlanAgent": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Parameters": {
        "FunctionName": "agent-plan",
        "Payload": {
          "ticket.$": "$.ticket",
          "repoSha.$": "$.repoSha"
        }
      },
      "ResultPath": "$.plan",
      "Next": "HumanApprovePlan",
      "Retry": [{
        "ErrorEquals": ["Bedrock.ThrottlingException", "States.Timeout"],
        "IntervalSeconds": 5, "MaxAttempts": 4, "BackoffRate": 2.0
      }]
    },
    "HumanApprovePlan": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke.waitForTaskToken",
      "TimeoutSeconds": 86400,
      "HeartbeatSeconds": 3600,
      "Parameters": {
        "FunctionName": "notify-slack-approval",
        "Payload": {
          "taskToken.$": "$$.Task.Token",
          "plan.$": "$.plan",
          "executionArn.$": "$$.Execution.Id"
        }
      },
      "ResultPath": "$.approval",
      "Next": "ImplementMap"
    },
    "ImplementMap": {
      "Type": "Map",
      "ItemsPath": "$.plan.Payload.fileBatches",
      "MaxConcurrency": 3,
      "Iterator": {
        "StartAt": "ImplementBatch",
        "States": {
          "ImplementBatch": {
            "Type": "Task",
            "Resource": "arn:aws:states:::lambda:invoke",
            "Parameters": {
              "FunctionName": "agent-implement",
              "Payload.$": "$"
            },
            "End": true
          }
        }
      },
      "ResultPath": "$.patches",
      "Next": "TestAgent"
    },
    "TestAgent": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Parameters": {
        "FunctionName": "agent-test",
        "Payload": { "patches.$": "$.patches", "repoSha.$": "$.repoSha" }
      },
      "ResultPath": "$.test",
      "Next": "ReviewGate"
    },
    "ReviewGate": {
      "Type": "Choice",
      "Choices": [{
        "Variable": "$.test.Payload.passed",
        "BooleanEquals": true,
        "Next": "OpenPrOnly"
      }],
      "Default": "FailClosed"
    },
    "OpenPrOnly": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Parameters": {
        "FunctionName": "open-draft-pr",
        "Payload": {
          "patches.$": "$.patches",
          "neverMerge": true
        }
      },
      "End": true
    },
    "FailClosed": {
      "Type": "Fail",
      "Error": "TestsFailed",
      "Cause": "Agent tests failed — no PR opened"
    }
  }
}

// notify-slack-approval.ts
import { SQSClient, SendMessageCommand } from "@aws-sdk/client-sqs";

export async function handler(event: {
  taskToken: string;
  plan: { Payload: { summary: string; blastRadius: string[] } };
  executionArn: string;
}) {
  // ✅ Park the token; humans resume via Slack action → SendTaskSuccess
  await new SQSClient({}).send(new SendMessageCommand({
    QueueUrl: process.env.APPROVAL_QUEUE!,
    MessageBody: JSON.stringify({
      taskToken: event.taskToken,
      executionArn: event.executionArn,
      summary: event.plan.Payload.summary,
      files: event.plan.Payload.blastRadius,
      expiresAt: Date.now() + 86_400_000,
    }),
  }));
}

// resume.ts — Slack interactivity handler
import { SFNClient, SendTaskSuccessCommand, SendTaskFailureCommand } from "@aws-sdk/client-sfn";

export async function resume(decision: "approve" | "reject", taskToken: string, actor: string) {
  const sfn = new SFNClient({});
  if (decision === "reject") {
    await sfn.send(new SendTaskFailureCommand({
      taskToken,
      error: "HumanRejected",
      cause: `rejected_by:${actor}`,
    }));
    return;
  }
  await sfn.send(new SendTaskSuccessCommand({
    taskToken,
    output: JSON.stringify({ approvedBy: actor, at: new Date().toISOString() }),
  }));
}

// open-draft-pr.ts — stamp the PR with the Step Functions execution
const body = [
  `## Agent pipeline`,
  `- Execution: \`${executionArn}\``,
  `- Plan approval: ${approval.approvedBy}`,
  `- Tests: ${test.Payload.summary}`,
  ``,
  `Do **not** merge until CODEOWNERS review. See [Agentic Git Workflows](https://cheatcoders.net/agentic-git-workflows-atomic-commits-from-noisy-llm-diffs/).`,
].join("\n");

# Cap fan-out and budget tokens per batch
MaxConcurrency: 3
# Inside agent-implement Lambda:
# - application inference profile
# - per-execution token budget from $.plan.Payload.tokenBudget