The IR fetch transport declared body as Uint8Array | undefined but returned
res.text(), crashing generated TS clients in TextDecoder.decode. Switch to
res.arrayBuffer() to match the contract, repeat array query params as
key=a&key=b with proper URL encoding, drop the Content-Type header override
that overwrote the spread with [null], and use status-code based body
detection so chunked responses without Content-Length work.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>