Bug: Upgrade to 3.7.0 breaks List response validation in APIGatewayRestResolver

[alnemo]

Expected Behaviour

3.6.0 and 3.7.0 behave the same

Current Behaviour

With powertools update to 3.7.0 same code returns 422 validation error, while it works on 3.6.0

Code snippet

from aws_lambda_powertools.event_handler import APIGatewayRestResolver, Response
import json
from pydantic import BaseModel
from typing import List

app = APIGatewayRestResolver(enable_validation=True)

class StatusGroup(BaseModel):
    count: int
    status: str   

def lambda_handler(event, context):
    return app.resolve(event,context)

@app.get("/status", 
        summary="status",
        description="count",
        response_description="status count",
        responses={
            200: {"description": "status count"}
        }
    )
def status( requests:List[str]) -> List[StatusGroup]:
    response = [{"status":"initial","count":1},{"status":"done","count":1}]
    return Response(200, body=json.dumps(response))

def main():
    event = {
        "path": "/status",
        "httpMethod": "GET",
        "requestContext": {"requestId": "227b78aa-779d-47d4-a48e-ce62120393b8"}, 
        "body": '["1","2","3"]'
    }
    response = lambda_handler(event,None)
    print(json.dumps(response,sort_keys=True, indent=4, default=str))

if __name__ == "__main__":
    main()

Possible Solution

No response

Steps to Reproduce

Run the example code while 3.6.0 or below is installed
pip install --upgrade aws-lambda-powertools==3.6.0
Response is
{
"body": "[{"status": "initial", "count": 1}, {"status": "done", "count": 1}]",
"isBase64Encoded": false,
"multiValueHeaders": {},
"statusCode": 200
}
Upgrade to 3.7.0
pip install --upgrade aws-lambda-powertools==3.7.0
Response is now
{
"body": "{"statusCode":422,"detail":[{"loc":["response"],"type":"list_type"}]}",
"isBase64Encoded": false,
"multiValueHeaders": {
"Content-Type": [
"application/json"
]
},
"statusCode": 422
}

Powertools for AWS Lambda (Python) version

3.7.0

AWS Lambda function runtime

3.12

Packaging format used

PyPi

Debugging logs

[leandrodamascena]

Hi @alnemo! Thank you so much for raising this issue! This PR introduced this unexpected regression. I see we don't have a test for it and that's why we didn't catch it before the merge.

We have a release scheduled for this Friday 07/03/2025 and I will revert this PR or fix this bug in this situation. Can you wait until then and adopt 3.8.0?

I'm really sorry about that.

[leandrodamascena]

Closed via #6234

[github-actions]

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[github-actions]

This is now released under 3.9.0 version!