When a model download proxy is configured, createProxyFetch() returned the
Response from undici's own fetch, which is not the global Response.
Transformers.js only writes `instanceof Response` results to its file cache,
so the ONNX weights were never cached and preload failed with "Unable to get
model file path or buffer." Keep undici's fetch and ProxyAgent, and re-wrap the
response body stream in a global Response.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: multica-agent <github@multica.ai>
