laidline-vllm

vLLM Model Runner V2 logits processor for the Laidline text watermark (SynthID or KGW), plus an ack-header middleware. It is the only marking that has to live outside the sidecar.

• Install it into vLLM's environment (it pulls in laidline[text]). The entry point vllm.logits_processors: laidline loads LaidlineTextWatermark with no flag needed; only requests that opt in are marked.
• LAIDLINE_CONFIG names the Laidline config. The processor reads watermark.text from it. With no config file, or with text watermarking disabled, the processor logs a warning and marks nothing. An invalid config file raises an error.
• It needs a vLLM with the Model Runner V2 logits-processor interface (vllm.v1.worker.gpu.sample.logits_processor). No release has it yet (not 0.19.1, not 0.30.0). The build tested on a GPU is nightly 0.30.1rc1.dev86+g5b3f280a6; export VLLM_USE_V2_MODEL_RUNNER=1 so vLLM cannot fall back to the V1 runner.
• A request opts in with vllm_xargs.laidline, an object with key_id and scheme (both optional). Over HTTP, send the object JSON-encoded, as in "vllm_xargs": {"laidline": "{\"key_id\": \"k1\", \"scheme\": \"synthid\"}"}. vLLM's OpenAI server accepts only strings, numbers and lists as vllm_xargs values, and answers 400 to a nested object. The Python LLM API also takes a plain dict in SamplingParams.extra_args["laidline"]. The Laidline proxy sends the JSON form for you.
• SynthID is skipped at temperature 0, so use scheme: kgw for greedy traffic. Speculative decoding is not supported: draft rows are left unmarked.
• --middleware laidline_vllm.middleware.ack_header adds x-laidline-watermarked: 1 and x-laidline-scheme (the config's scheme, unknown without a usable config) to every response. It means "plugin installed", not "this response was marked"; the Laidline proxy treats unknown as no ack and checks greedy decoding itself. Use the dotted path: vLLM splits it on the last ., in 0.19.1 and in the tested nightly alike. The module:function form fails at startup.

Proven live on an RTX 5080 (SynthID and KGW, directly and through the proxy). Full guide: https://laidline.com/docs/integrations/vllm.