Custom Providers — fromFetch

For a provider with no SDK, or where pulling one in isn't worth it, fromFetch is a raw HTTP escape hatch — supply the URL, headers, and two small mapping functions, and retries/timeouts/circuit-breaker/JSON handling all still apply.

import { VernLLM, fromFetch } from 'vern-llm';

const llm = new VernLLM({
  client: fromFetch({
    url: 'https://api.example.com/v1/generate',
    headers: () => ({ Authorization: `Bearer ${process.env.EXAMPLE_API_KEY}` }),
    mapRequest: (params) => ({
      model: params.model,
      prompt: params.messages.map((m) => m.content).join('\n\n'),
      max_tokens: params.max_tokens,
    }),
    mapResponse: (json) => ({
      content: json.output,
      usage: { promptTokens: json.usage?.input, completionTokens: json.usage?.output },
    }),
  }),
  model: 'example-model-v1',
});

Non-2xx responses throw with .status set, so nonRetryableStatus still fails fast on 401/403 as usual.