AWS model cache

The conformance suite reads api-2.json from the Go module cache for the pinned github.com/aws/aws-sdk-go version v1.55.8. Running Go tests or go mod download populates that cache; the large upstream model files are intentionally not tracked in this repository.

ec2/error-codes.json is separate from the SDK models because EC2's api-2.json declares no operation errors. It is a curated subset of the official EC2 error-code reference: all documented common and server codes, plus the action-specific codes that Spinifex currently emits. The catalog records its verification date and must be reviewed against that source when it changes.