dsh-image-base64

A DeepSeek Harness plugin that fixes:

This turn failed 400 "'url' field must be a base64 encoded image."
INVALID_REQUEST

when a vision-capable model (e.g. meta/muse-glimmer) is served through an OpenAI-compatible gateway that validates the image MIME type strictly, such as LM Studio.

Why this happens

See deepseek-ai/deepseek-harness#4615 for the full discussion. The short version:

• dsh-attachment-local's request-image quality ladder re-encodes an image as image/webp whenever the source has an alpha channel (JPEG has no alpha channel to fall back to). A pasted screenshot or a PNG with transparency very often has one.
• LM Studio's OpenAI-compatible endpoint only accepts image/png, image/jpeg, and image/gif inside a base64 data: URL. It rejects image/webp (and anything else) at the protocol layer with 400, before the request reaches the model.
• dsh-llm-pi-ai forwards whatever mediaType the attachment store gives it straight into the request — there's no format negotiation between the two, so the mismatch reaches LM Studio unchanged.

What this plugin does

It wraps the attachment store's readImageRequest() (the call dsh-llm-pi-ai makes to get the exact bytes/MIME type that go into the request) and transcodes the result to image/png with sharp whenever its media type isn't in an accepted list (image/png, image/jpeg, image/gif by default). Everything already in an accepted format passes through untouched — only the images that would otherwise be rejected pay the transcode cost.

Install

From your DSH profile directory (or via dsh plugin --profile <name> add, which forwards to pnpm inside the profile):

dsh plugin --profile <name> add /home/pakkapon/dsh-image-base64

Then list it in that profile's package.json under dsh.profile.bundles:

{
  "dsh": {
    "profile": {
      "bundles": [
        "@deepseek-ai/dsh-base",
        "@deepseek-ai/dsh-web-app",
        "dsh-image-base64"
      ]
    }
  }
}

Restart the profile (or let it pick it up automatically if patchReload: live is set) to load it.

Configuration

Accepted media types default to [image/png, image/jpeg, image/gif] (LM Studio's whitelist). To widen or narrow that, target the plugin's id from your own patch layer (profile cordis.patch.yml or $DSH_HOME/cordis.patch.yml):

- id: image-base64-compat
  config:
    acceptedMediaTypes: [image/png, image/jpeg, image/gif, image/webp]

Caveats

• This patches the attachment store's request-image projection only — it doesn't touch how images are stored, just what's sent on the wire for a model request.
• Transcoding to PNG is lossless for the pixels it's given, but a PNG re-encode of a large photo is bigger than an equivalent JPEG/WebP. If your gateway actually accepts WebP, add it to acceptedMediaTypes instead of relying on the default.

License

MIT