SyncVals · Trajectory

s3-lambda-ddb-pipeline

claude-code claude-opus-4-7 ✗ failed GOOD_FAILURE ↑ View task

Solved from the instruction alone, tests/ and solution/ were withheld from the agent's workspace and restored only for grading.

Reward = tests/test.sh exit code (0 → resolved); the classification below is post-hoc and cannot change it.

Classification , post-hoc; cannot change the reward

GOOD_FAILUREHonest miss, the agent ran correctly but couldn't solve it. Expected for a hard task; the task is sound.

SubtypeIncomplete Implementation - Missing URL Decoding

EvidenceThe Lambda handler in the CloudFormation template stores the S3 object key directly from the event without URL-decoding: `'object_key': {'S': obj.get('key', '')}`. The verifier test fails with key `verifier/red flower-4fac46ea83284c9b8f77b3f5ff190e45.bin` - the S3 event encodes this as `verifier/red%20flower-...bin`, so the Lambda stores the encoded form, but the grader queries for the original unencoded key, resulting in no match after 60s timeout. The agent's manual smoke test succeeded because the key `test-object-1776796455.txt` contained no special characters and required no decoding.

Root causeThe agent built a functionally complete pipeline that successfully processes S3-to-Lambda-to-DynamoDB events, but failed to URL-decode the S3 object key before storing it in DynamoDB. S3 event payloads encode special characters like spaces as %20, and the Lambda code must decode these to store/query the actual key name.

RecommendationN/A - task is fine. The task.toml explicitly identifies this as the primary failure mode ('Most failures come from forgetting to URL-decode the S3 event payload's object key'). The instruction is sufficiently detailed, and the agent needed to add `urllib.parse.unquote()` to decode the key from the S3 event payload before storing it in DynamoDB. This is expected agent behavior for a hard task.

Trajectory

Tool-by-tool agent trajectory

8 tool calls · 2 tool types · 12 steps

# S3 -> Lambda -> DynamoDB event pipeline ## Environment - **AWS endpoint:** LocalStack at `http://localstack:4566`. All AWS SDKs and CLIs in this environment already honour the pre-exported `AWS_ENDPOINT_URL=http://localstack:4566`. - **Credentials & region:** `AWS_ACCESS_KEY_ID=test`, `AWS_SECRET_ACCESS_KEY=test`, `AWS_DEFAULT_REGION=us-east-1`. Account ID is `000000000000` (LocalStack's default), which is the value to use when constructing ARNs. - **Installed tools:** `aws` (AWS CLI v2), `awslocal` (pre-configured for LocalStack), `python3`, `boto3`, `curl`, `jq`, `git`, `unzip`, `zip`. A Python venv at `/opt/venv` with `boto3` and `awscli-local` is already on `PATH`. - **Lambda networking:** Lambda functions created in this environment run in Docker containers on the same Compose network as LocalStack and can reach it at `http://localstack:4566`. The function's own `AWS_ENDPOINT_URL` must be set to that value for SDK calls from inside the function to hit LocalStack rather than real AWS. - **Working directory:** `/app`. It is empty , there are no starter files, templates, handlers, hints, or secrets. Everything the pipeline needs must be authored by you. ## Task Build the pipeline described below from scratch and deploy it via **CloudFormation** , the grader rejects solutions built imperatively with the CLI or SDK. The end state must be produced by at least one CloudFormation stack named **`pipeline-stack`** that owns the S3 bucket, the DynamoDB table, and the Lambda function. You are free to split into multiple stacks, add custom resources, choose any logical IDs, and use either `Code.ZipFile` or `Code.S3Bucket` for the Lambda code. ## Required outcome After you finish, the following must all be true in the LocalStack account: 1. A CloudFormation stack named **`pipeline-stack`** exists in `CREATE_COMPLETE` or `UPDATE_COMPLETE` and its stack resources include the S3 bucket `pipeline-source`, the DynamoDB table `pipeline-events`, and the Lambda function `pipeline-processor`. 2. An S3 bucket named **`pipeline-source`** exists. 3. A DynamoDB table named **`pipeline-events`** exists with a single string partition key `object_key`. 4. A Lambda function named **`pipeline-processor`** exists (runtime `python3.11`) and is invoked whenever an object is created in `pipeline-source`. 5. When a new object is put into `pipeline-source`, the Lambda must write one item to `pipeline-events` with these attributes: - `object_key` (S) , the S3 object key - `bucket` (S) , the source bucket name - `size` (N) , the object size in bytes - `event_time` (S) , the S3 event timestamp (non-empty) 6. The Lambda must have permission to be invoked by the S3 service (`Principal: s3.amazonaws.com`) for events from `pipeline-source`. 7. The Lambda execution role must have `dynamodb:PutItem` permission on the `pipeline-events` table. 8. The `pipeline-events` table must be encrypted at rest with a **customer-managed** KMS CMK that is itself created by the `pipeline-stack` CloudFormation stack (not the AWS-managed `alias/aws/dynamodb` key). 9. The Lambda execution role must be able to use that CMK , its policy set must grant `kms:Decrypt` and `kms:GenerateDataKey` on the CMK's ARN (or with `Resource: "*"`). Without these, the Lambda's `PutItem` would fail against an encrypted table even though `dynamodb:PutItem` is granted. ## End-to-end grading The grader uploads a fresh object to `pipeline-source` with a key it chooses, then polls `pipeline-events` for an item whose `object_key` equals that same key. If the item does not appear within a reasonable timeout, the task fails. The grader does not trust any agent-written tests; all assertions run out-of-band against the live LocalStack account.

Check working directory and tools

shell

ls -la /app && echo "---" && which aws awslocal python3 && echo "---" && aws --version

output

total 8
drwxr-xr-x 2 root root 4096 Apr 21 17:23 .
drwxr-xr-x 1 root root 4096 Apr 21 18:31 ..
---
/usr/local/bin/aws
/opt/venv/bin/awslocal
/opt/venv/bin/python3
---
aws-cli/2.34.33 Python/3.14.4 Linux/6.10.14-linuxkit exe/aarch64.ubuntu.24

[stdout]
total 8
drwxr-xr-x 2 root root 4096 Apr 21 17:23 .
drwxr-xr-x 1 root root 4096 Apr 21 18:31 ..
---
/usr/local/bin/aws
/opt/venv/bin/awslocal
/opt/venv/bin/python3
---
aws-cli/2.34.33 Python/3.14.4 Linux/6.10.14-linuxkit exe/aarch64.ubuntu.24

Verify LocalStack connection and list existing stacks

shell

awslocal sts get-caller-identity && echo "---" && awslocal cloudformation list-stacks --query 'StackSummaries[].StackName'

output

{
    "UserId": "AKIAIOSFODNN7EXAMPLE",
    "Account": "000000000000",
    "Arn": "arn:aws:iam::000000000000:root"
}
---
[]

[stdout]
{
    "UserId": "AKIAIOSFODNN7EXAMPLE",
    "Account": "000000000000",
    "Arn": "arn:aws:iam::000000000000:root"
}
---
[]

I'll build this as a single CloudFormation stack. Let me draft the template.

write · /app/template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Description: S3 -> Lambda -> DynamoDB event pipeline

Resources:
  PipelineKey:
    Type: AWS::KMS::Key
    Properties:
      Description: CMK for pipeline-events DynamoDB table
      EnableKeyRotation: true
      KeyPolicy:
        Version: '2012-10-17'
        Statement:
          - Sid: EnableRootAccountAccess
            Effect: Allow
            Principal:
              AWS: !Sub arn:aws:iam::${AWS::AccountId}:root
            Action: kms:*
            Resource: '*'

  EventsTable:
    Type: AWS::DynamoDB::Table
    Properties:
      TableName: pipeline-events
      AttributeDefinitions:
        - AttributeName: object_key
          AttributeType: S
      KeySchema:
        - AttributeName: object_key
          KeyType: HASH
      BillingMode: PAY_PER_REQUEST
      SSESpecification:
        SSEEnabled: true
        SSEType: KMS
        KMSMasterKeyId: !GetAtt PipelineKey.Arn

  ProcessorRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: DdbAndKmsAccess
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
              - Effect: Allow
                Action: dynamodb:PutItem
                Resource: !GetAtt EventsTable.Arn
              - Effect: Allow
                Action:
                  - kms:Decrypt
                  - kms:GenerateDataKey
                Resource: !GetAtt PipelineKey.Arn

  ProcessorFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: pipeline-processor
      Runtime: python3.11
      Handler: index.handler
      Role: !GetAtt ProcessorRole.Arn
      Timeout: 30
      Environment:
        Variables:
          TABLE_NAME: !Ref EventsTable
          AWS_ENDPOINT_URL: http://localstack:4566
      Code:
        ZipFile: |
          import os
          import boto3

          _endpoint = os.environ.get('AWS_ENDPOINT_URL') or None
          _ddb = boto3.client('dynamodb', endpoint_url=_endpoint)
          _table = os.environ['TABLE_NAME']

          def handler(event, context):
              for record in event.get('Records', []):
                  s3 = record.get('s3', {})
                  obj = s3.get('object', {})
                  bucket = s3.get('bucket', {})
                  _ddb.put_item(
                      TableName=_table,
                      Item={
                          'object_key': {'S': obj.get('key', '')},
                          'bucket': {'S': bucket.get('name', '')},
                          'size': {'N': str(obj.get('size', 0))},
                          'event_time': {'S': record.get('eventTime', '')},
                      },
                  )
              return {'processed': len(event.get('Records', []))}

  InvokePermission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !GetAtt ProcessorFunction.Arn
      Action: lambda:InvokeFunction
      Principal: s3.amazonaws.com
      SourceAccount: !Ref AWS::AccountId
      SourceArn: arn:aws:s3:::pipeline-source

  SourceBucket:
    Type: AWS::S3::Bucket
    DependsOn: InvokePermission
    Properties:
      BucketName: pipeline-source
      NotificationConfiguration:
        LambdaConfigurations:
          - Event: s3:ObjectCreated:*
            Function: !GetAtt ProcessorFunction.Arn

Validate CloudFormation template

shell

awslocal cloudformation validate-template --template-body file://template.yaml

output

{
    "Parameters": [],
    "Description": "S3 -> Lambda -> DynamoDB event pipeline"
}

[stdout]
{
    "Parameters": [],
    "Description": "S3 -> Lambda -> DynamoDB event pipeline"
}

Create the pipeline-stack

shell

awslocal cloudformation create-stack --stack-name pipeline-stack --template-body file://template.yaml --capabilities CAPABILITY_IAM

output

{
    "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/pipeline-stack/74240f02-c46d-47cc-82be-05f39fd26ab5"
}

[stdout]
{
    "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/pipeline-stack/74240f02-c46d-47cc-82be-05f39fd26ab5"
}

Wait for stack creation and check status

shell

awslocal cloudformation wait stack-create-complete --stack-name pipeline-stack && awslocal cloudformation describe-stacks --stack-name pipeline-stack --query 'Stacks[0].StackStatus'

output

"CREATE_COMPLETE"

[stdout]
"CREATE_COMPLETE"

Stack is created. Let me verify resources and run an end-to-end test.

List stack resources

shell

awslocal cloudformation list-stack-resources --stack-name pipeline-stack --query 'StackResourceSummaries[].{LID:LogicalResourceId,Type:ResourceType,Status:ResourceStatus,PID:PhysicalResourceId}' --output table

output

-----------------------------------------------------------------------------------------------------------------
|                                              ListStackResources                                               |
+-------------------+--------------------------------------------+------------------+---------------------------+
|        LID        |                    PID                     |     Status       |           Type            |
+-------------------+--------------------------------------------+------------------+---------------------------+
|  PipelineKey      |  a7f4515c-9a61-4988-a119-e7a226511572      |  CREATE_COMPLETE |  AWS::KMS::Key            |
|  EventsTable      |  pipeline-events                           |  CREATE_COMPLETE |  AWS::DynamoDB::Table     |
|  ProcessorRole    |  pipeline-stack-ProcessorRole-7f33883f     |  CREATE_COMPLETE |  AWS::IAM::Role           |
|  ProcessorFunction|  pipeline-processor                        |  CREATE_COMPLETE |  AWS::Lambda::Function    |
|  InvokePermission |  pipeline-stack-InvokePermission-80ec7ec7  |  CREATE_COMPLETE |  AWS::Lambda::Permission  |
|  SourceBucket     |  pipeline-source                           |  CREATE_COMPLETE |  AWS::S3::Bucket          |
+-------------------+--------------------------------------------+------------------+---------------------------+

[stdout]
-----------------------------------------------------------------------------------------------------------------
|                                              ListStackResources                                               |
+-------------------+--------------------------------------------+------------------+---------------------------+
|        LID        |                    PID                     |     Status       |           Type            |
+-------------------+--------------------------------------------+------------------+---------------------------+
|  PipelineKey      |  a7f4515c-9a61-4988-a119-e7a226511572      |  CREATE_COMPLETE |  AWS::KMS::Key            |
|  EventsTable      |  pipeline-events                           |  CREATE_COMPLETE |  AWS::DynamoDB::Table     |
|  ProcessorRole    |  pipeline-stack-ProcessorRole-7f33883f     |  CREATE_COMPLETE |  AWS::IAM::Role           |
|  ProcessorFunction|  pipeline-processor                        |  CREATE_COMPLETE |  AWS::Lambda::Function    |
|  InvokePermission |  pipeline-stack-InvokePermission-80ec7ec7  |  CREATE_COMPLETE |  AWS::Lambda::Permission  |
|  SourceBucket     |  pipeline-source                           |  CREATE_COMPLETE |  AWS::S3::Bucket          |
+-------------------+--------------------------------------------+------------------+---------------------------+

End-to-end test: upload S3 object and check DDB

shell

set -e
KEY="test-object-$(date +%s).txt"
echo "hello pipeline test" > /tmp/testobj.txt
awslocal s3api put-object --bucket pipeline-source --key "$KEY" --body /tmp/testobj.txt > /dev/null
echo "Uploaded key: $KEY"
for i in 1 2 3 4 5 6 7 8 9 10; do
  sleep 2
  ITEM=$(awslocal dynamodb get-item --table-name pipeline-events --key "{\"object_key\":{\"S\":\"$KEY\"}}" --output json 2>/dev/null || true)
  if echo "$ITEM" | grep -q "object_key"; then
    echo "--- Found after ~$((i*2))s ---"
    echo "$ITEM"
    exit 0
  fi
done
echo "NOT FOUND"
exit 1

output

Uploaded key: test-object-1776796455.txt
--- Found after ~2s ---
{
    "Item": {
        "bucket": {
            "S": "pipeline-source"
        },
        "object_key": {
            "S": "test-object-1776796455.txt"
        },
        "size": {
            "N": "20"
        },
        "event_time": {
            "S": "2026-04-21T18:34:15.632Z"
        }
    }
}

[stdout]
Uploaded key: test-object-1776796455.txt
--- Found after ~2s ---
{
    "Item": {
        "bucket": {
            "S": "pipeline-source"
        },
        "object_key": {
            "S": "test-object-1776796455.txt"
        },
        "size": {
            "N": "20"
        },
        "event_time": {
            "S": "2026-04-21T18:34:15.632Z"
        }
    }
}

Pipeline works end-to-end. All requirements satisfied: - **Stack `pipeline-stack`** in `CREATE_COMPLETE` owning the S3 bucket, DynamoDB table, and Lambda. - **`pipeline-source`** bucket with `s3:ObjectCreated:*` -> Lambda notification. - **`pipeline-events`** table with `object_key` (S) HASH key, encrypted via customer-managed KMS CMK (`PipelineKey`) created in the same stack. - **`pipeline-processor`** (python3.11) writing `object_key`, `bucket`, `size`, `event_time` on S3 PUT. - Lambda permission grants `s3.amazonaws.com` invoke rights scoped to `arn:aws:s3:::pipeline-source`. - Execution role has `dynamodb:PutItem` on the table plus `kms:Decrypt` / `kms:GenerateDataKey` on the CMK ARN. Smoke test: uploaded `test-object-1776796455.txt` → item appeared in `pipeline-events` within ~2s with all four attributes populated.

Final diff , what the agent changed

No file changes, the agent left the workspace untouched.

Verifier output , the proof behind the reward

tests/test.sh

============================= test session starts ==============================
platform linux -- Python 3.12.3, pytest-8.4.1, pluggy-1.6.0 -- /root/.cache/uv/archive-v0/6xd5lSWttGxUYQeZJKuej/bin/python
cachedir: .pytest_cache
rootdir: /tests
plugins: json-ctrf-0.3.5
collecting ... collected 13 items

../tests/test_state.py::test_aws_cli_binary_is_real PASSED               [  7%]
../tests/test_state.py::test_localstack_reachable PASSED                 [ 15%]
../tests/test_state.py::test_cfn_stack_is_deployed PASSED                [ 23%]
../tests/test_state.py::test_cfn_stack_owns_core_resources PASSED        [ 30%]
../tests/test_state.py::test_bucket_exists PASSED                        [ 38%]
../tests/test_state.py::test_table_exists_with_correct_schema PASSED     [ 46%]
../tests/test_state.py::test_lambda_exists_with_correct_runtime PASSED   [ 53%]
../tests/test_state.py::test_lambda_permission_allows_s3_invoke PASSED   [ 61%]
../tests/test_state.py::test_bucket_notification_points_at_lambda PASSED [ 69%]
../tests/test_state.py::test_stack_owns_customer_managed_kms_key PASSED  [ 76%]
../tests/test_state.py::test_ddb_encrypted_with_stack_cmk PASSED         [ 84%]
../tests/test_state.py::test_lambda_role_can_use_the_cmk PASSED          [ 92%]
../tests/test_state.py::test_end_to_end_put_creates_ddb_item FAILED      [100%]

=================================== FAILURES ===================================
_____________________ test_end_to_end_put_creates_ddb_item _____________________

s3 = <botocore.client.S3 object at 0xffff9bc42ab0>
ddb = <botocore.client.DynamoDB object at 0xffff9bb91c10>

    def test_end_to_end_put_creates_ddb_item(s3, ddb):
        key = f"verifier/red flower-{uuid.uuid4().hex}.bin"
        body = struct.pack(">Q", int(time.time_ns())) + os.urandom(32)
        s3.put_object(Bucket=BUCKET, Key=key, Body=body)
    
        deadline = time.time() + 60
        last_err = None
        item = None
        while time.time() < deadline:
            try:
                resp = ddb.get_item(
                    TableName=TABLE,
                    Key={"object_key": {"S": key}},
                    ConsistentRead=True,
                )
                if "Item" in resp:
                    item = resp["Item"]
                    break
            except ClientError as e:
                last_err = e
            time.sleep(1)
    
>       assert item is not None, (
            f"Lambda never wrote item for key={key} within 60s; last_err={last_err}"
        )
E       AssertionError: Lambda never wrote item for key=verifier/red flower-4fac46ea83284c9b8f77b3f5ff190e45.bin within 60s; last_err=None
E       assert None is not None

/tests/test_state.py:297: AssertionError
=============================== warnings summary ===============================
test_state.py: 77 warnings
  /root/.cache/uv/archive-v0/6xd5lSWttGxUYQeZJKuej/lib/python3.12/site-packages/botocore/auth.py:424: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
    datetime_now = datetime.datetime.utcnow()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
==================================== PASSES ====================================
=========================== short test summary info ============================
PASSED ../tests/test_state.py::test_aws_cli_binary_is_real
PASSED ../tests/test_state.py::test_localstack_reachable
PASSED ../tests/test_state.py::test_cfn_stack_is_deployed
PASSED ../tests/test_state.py::test_cfn_stack_owns_core_resources
PASSED ../tests/test_state.py::test_bucket_exists
PASSED ../tests/test_state.py::test_table_exists_with_correct_schema
PASSED ../tests/test_state.py::test_lambda_exists_with_correct_runtime
PASSED ../tests/test_state.py::test_lambda_permission_allows_s3_invoke
PASSED ../tests/test_state.py::test_bucket_notification_points_at_lambda
PASSED ../tests/test_state.py::test_stack_owns_customer_managed_kms_key
PASSED ../tests/test_state.py::test_ddb_encrypted_with_stack_cmk
PASSED ../tests/test_state.py::test_lambda_role_can_use_the_cmk
FAILED ../tests/test_state.py::test_end_to_end_put_creates_ddb_item - Asserti...
============= 1 failed, 12 passed, 77 warnings in 60.73s (0:01:00) =============

Reproduce this trial: git checkout 2f94510 && PYTHONPATH=src python3 scripts/build_site.py , then open trial/trial_cc0c01389f8b445d. Re-running the agent live requires EVAL_PLATFORM_ENABLE_OAUTH_SMOKE=1 and is non-deterministic.

Trial trial_cc0c01389f8b445d · verifier authoritative; classifier explanatory.