CVE-2026-84379: HTTPX2: Multipart part header injection via unvalidated file Content-Type and custom headers

HTTPX2 serializes the per-file Content-Type and custom headers supplied through the files= tuple API directly into the multipart/form-data body without validating custom header names or values. An attacker who can influence upload metadata passed to HTTPX2 can use CR or LF characters to terminate a multipart part header and inject additional part headers or end the part header block early.