gh release upload of large files fails with "tls: bad record MAC" through Bash sandbox proxy

Bug

gh release upload of any release asset larger than ~a few MB consistently fails with remote error: tls: bad record MAC when run from the Claude Code Bash tool. The same command from a regular Terminal.app (outside Claude Code's environment) succeeds with the same network and same gh credentials.

Reproduction

1. From Claude Code's Bash tool, build any large file (e.g. a 185 MB zip)
2. Run: gh release upload v0.X.Y build/large.zip --clobber
3. Result: Post "https://uploads.github.com/repos/owner/repo/releases/N/assets?...": remote error: tls: bad record MAC

What I tested to narrow it down

• Small upload through same proxy: 16-byte text file uploaded fine to the same release ✓
• Large upload from regular Terminal.app: succeeds (with normal proxy / no-proxy environment)
• gh release create (small JSON POST): succeeds through same Claude Code env ✓
• dangerouslyDisableSandbox: true: still fails — proxy env vars remain set
• env -u HTTP_PROXY -u HTTPS_PROXY -u ALL_PROXY gh release upload ...: fails with "error connecting to api.github.com" (network requires Claude Code's proxy to reach GitHub at all)
• Drop only ALL_PROXY (keep HTTPS_PROXY): same TLS error → not a SOCKS-vs-HTTP-CONNECT issue
• Pattern matches reports of similar Go HTTP client + local proxy + large streaming POST: rclone#1893, rclone#3338, googleapis/google-cloud-go#1581 — all attribute it to proxy-side buffering corrupting long TLS streams

Diagnosis

Claude Code's local sandbox proxy (ports 65166 HTTP / 65167 SOCKS5 in my session) appears to corrupt bytes during long-running streaming HTTPS uploads, breaking TLS record MAC verification on uploads.github.com. Small requests through the same proxy work fine; the bug only triggers on multi-second streaming uploads.

This blocks gh release upload (and presumably any other Go-based tool doing chunked/streaming HTTPS uploads to allow-listed hosts) from inside Claude Code.

Environment

• Claude Code: 2.1.138
• macOS: 26.4.1 (Darwin 25.4.0)
• gh CLI: 2.92.0
• uploads.github.com is in the host allowlist (small uploads pass)

Workaround

Run gh release upload from a regular Terminal.app outside Claude Code.

Suggested investigation

The Bash tool's sandbox proxy implementation — likely a Go HTTP CONNECT proxy / SOCKS5 proxy — needs to handle long-running upload streams without buffering or re-segmenting the TLS payload. This was apparently working in earlier Claude Code versions and regressed.