dsh-image-base64

When routing vision-model requests through an OpenAI-compatible gateway that enforces a strict MIME whitelist—LM Studio being the most common offender—screenshots or PNGs with an alpha channel get re-encoded to WebP upstream, and the gateway rejects the payload with a 400 before it ever reaches the model.

This plugin wraps the attachment store's readImageRequest() call (the exact point where dsh-llm-pi-ai fetches bytes and MIME type for the wire) and transcodes the result to PNG via sharp only when the media type falls outside an accepted list (image/png, image/jpeg, image/gif by default). Already-accepted formats pass through untouched, so the transcode cost is paid exclusively by images that would otherwise be rejected.

It is designed for anyone whose vision pipeline goes through a gateway with a rigid MIME whitelist, particularly LM Studio users who paste screenshots or attach transparent PNGs. If your gateway does accept WebP, you can narrow the acceptedMediaTypes list via a patch layer to skip the redundant PNG re-encode.