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nb; this is a self contained test stack. Nothing else points to it, so I'm not sure what the "active stages pointing to this deployment" might be

the stages it’s referring to are AWS API Gateway stages, e.g. https://docs.aws.amazon.com/apigateway/latest/developerguide/stages.html

Seems like there are a few bugs filed against Terraform with this error message specifically in regards to the API Gateway. Just guessing, but maybe you can try Crosswalk (https://www.pulumi.com/docs/guides/crosswalk/aws/api-gateway/) to avoid this problem?

Ok, that makes the error make more sense. If I'm not mistaken the Crosswalk api is the awsx module? If so, that is indeed what I was using. Looking through the AWS console everything seems pretty much how I would expect. There was a stage listed against the API Gateway, and deleting it manually failed to resolve the issue. I'm going to drop the entire stack manually, delete the pulumi entry and try again.