dsh-vision-3090-fix

A DeepSeek Harness (dsh) plugin that fixes:

400: {"message":"At most 1 image(s) may be provided in one prompt. (parameter=image)","type":"BadRequestError","param":"image","code":400}

against a self-hosted OpenAI-compatible vision backend (e.g. syv-ai/qwen38-27b-rtx3090, a single-RTX-3090 vLLM deployment). vLLM serves these models with --limit-mm-per-prompt image=1, so any request carrying more than one image content part is rejected with a 400 — even across unrelated turns of the same conversation, and even across separate tool calls (e.g. a screenshot tool and a file-pull tool each returning one image) in the same turn.

Why this happens

Harness's shipped LLM adapters (dsh-llm-pi-ai, dsh-llm-deepseek) only offload images by accumulated byte size (maxRequestImageBytes / requestImageMaxBytes). They never cap by count. So a conversation where you attach one small image, get a reply, and then attach a second small image sends both images in the next request — comfortably under any byte budget, but two images, which this backend refuses outright.

What this plugin does

It's a small local HTTP reverse proxy, started as an ordinary Cordis plugin effect (see docs/user/develop/basic/index.md#automatic-cleanup in the harness docs — ctx.effect() starts and stops it with the plugin's lifecycle). You put it in front of your existing provider's baseURL; everything else about how you already talk to the backend — dsh-llm-pi-ai's pure provider, its model list, its credential — stays exactly as configured.

For each forwarded request, the proxy:

1. Parses the JSON body's messages array (standard OpenAI wire format).
2. Counts every image_url content part across the whole array, including ones nested in tool-role messages (a returned screenshot, a pulled file).
3. Replaces every one beyond the newest maxImagesPerRequest (default 1) with a stable text placeholder, in place.
4. Forwards the request — headers (including Authorization, untouched — the proxy never needs or sees your API key's meaning, just passes it through) and the rewritten body — to the real backend.
5. Streams the response straight back, byte for byte, so SSE streaming works exactly as it would talking to the backend directly (verified: chunks arrive incrementally, not buffered).

A request already at or under the cap is forwarded completely unmodified.

Install

dsh plugin --profile web add /path/to/dsh-vision-3090-fix

(or dsh plugin --profile web add github:pureexe/dsh-vision-3090-fix once pushed).

Configure it in your profile's cordis.patch.yml (e.g. ~/.dsh/profiles/web/cordis.patch.yml):

- id: vision-3090-fix
  name: dsh-vision-3090-fix
  config:
    upstreamOrigin: http://10.204.100.243:1234   # scheme+host+port only, no path
    listenHost: 127.0.0.1
    listenPort: 8931
    maxImagesPerRequest: 1                        # match your server's --limit-mm-per-prompt
    models: [qwen3.8-27b]                         # optional; omit to cap every model

baseURL in dsh-llm-pi-ai is set once per provider, not per model — every model listed under that one provider shares it. So if pure serves three models and you point its baseURL at this proxy, all three now go through the proxy, even though only one of them needs the cap. models (optional; empty means "cap everything") scopes the cap itself, not the routing: out-of-scope requests still take the extra local hop through the proxy, but are forwarded completely untouched — same bytes in, same bytes out, no behavior change from talking to the backend directly.

Then point your existing provider config at the proxy instead of the real backend — the only line that changes. For a dsh-llm-pi-ai route in settings.yaml:

llm-pi-ai:
  providers:
    pure:
      displayName: pure
      apiKeyEnv: PURE_API_KEY
      api: openai-completions
      baseURL: http://127.0.0.1:8931/v1   # was: http://10.204.100.243:1234/v1
      models:
        - id: qwen3.8-27b
          # ...unchanged

Everything else — credentials, model list, agent-default-model, the Web UI's Models settings page — keeps working exactly as it did before, because dsh-llm-pi-ai still owns the pure route and is still the thing editing/reading that section. The proxy is invisible to it beyond the URL.

Configuration reference

Field	Default	Meaning
upstreamOrigin	(required)	Scheme+host+port of the real backend, e.g. http://10.204.100.243:1234 — no path
listenHost	127.0.0.1	Host the proxy listens on
listenPort	(required)	Port the proxy listens on; point your provider's baseURL at http://<listenHost>:<listenPort>/v1
maxImagesPerRequest	1	Images kept per forwarded request; excess (oldest first) becomes placeholder text
models	[] (every model)	Model ids the cap applies to (matched against the request's model field); every other model is forwarded byte-for-byte untouched
verbose	false	Log the startup banner and each request that gets capped. Actual proxy errors (e.g. the upstream is unreachable) are always logged regardless — they aren't routine noise.

Testing

npm install
npm test                # unit + local end-to-end tests (fake upstream, no network)

To also run the end-to-end test against the real backend:

VISION_3090_FIX_LIVE_UPSTREAM=http://10.204.100.243:1234 \
VISION_3090_FIX_LIVE_API_KEY=<your-api-key> \
VISION_3090_FIX_LIVE_MODEL=qwen3.8-27b \
VISION_3090_FIX_LIVE_IMAGE=/home/pakkapon/a.png \
node --test test/live.test.js

That test starts a real instance of the proxy, first proves an uncapped two-image conversation gets the reported 400 from the real backend, then proves the same conversation succeeds once proxied through a 1-image cap.

Known limitations

• Buffers the request body fully before forwarding (needed to parse and rewrite JSON); fine for chat/vision payloads, not meant for large file uploads. The response is streamed through without buffering.
• No retry logic and no request queuing — it's a thin pass-through, not a load balancer.
• Assumes the backend is plain HTTP/HTTPS chat/completions-shaped JSON; a provider using a different wire shape for images (not OpenAI's image_url content part) won't be recognized.

License

MIT