Oversized S3 assets fail Image Optimizer HEAD preflight #950

A signed S3 HEAD preflight for an Image Optimizer asset fails when the object Content-Length exceeds the adapter’s 10 MiB buffered-response limit.

HEAD responses contain no body; their Content-Length describes the corresponding GET representation. The Fastly adapter currently treats that metadata as a body it will buffer and rejects the preflight before the final streamed GET can run.

The adapter should preserve HEAD response headers while skipping body materialization and body-size enforcement. Buffered non-HEAD responses must retain the existing 10 MiB safety limit.