Go gateway: SSE streaming requests over HTTP/1.1 return HTTP 500 (Endpoint is unavailable)

Description

Summary

Streaming (SSE) chat completion requests to the opencode-go gateway endpoint https://opencode.ai/zen/go/v1/chat/completions return HTTP 500 with body {"type":"error","error":{"type":"error","message":"Internal server error"}} when sent over HTTP/1.1. The same request over HTTP/2 succeeds (HTTP 200 with normal SSE chunks). Non-streaming requests over HTTP/1.1 also succeed.

This surfaces in OpenChamber/openCode sessions as AI_APICallError: Upstream request failed: Endpoint is unavailable. for provider opencode-go (e.g. deepseek-v4-flash), in recurring bursts (retries all fail for several minutes, then recover).

Evidence

• HTTP/1.1 + stream:true -> always HTTP 500 (reproduced 10+ times)
• HTTP/1.1 non-streaming: HTTP 200 (5/5)
• HTTP/2 (node http2) + stream:true -> HTTP 200, normal SSE stream
• opencode CLI 1.18.18 (bun, HTTP/2) with opencode-go/deepseek-v4-flash works fine
• Request body/headers captured from the working client and replayed via curl over HTTP/1.1 still 500s: {"model":"deepseek-v4-flash","max_tokens":32000,"top_p":0.95,"messages":[...],"tool_choice":"auto","stream":true,"stream_options":{"include_usage":true}}

Expected

Streaming over HTTP/1.1 should work like any OpenAI-compatible endpoint (other providers do). Or at minimum return a meaningful status/error instead of a generic 500.

Plugins

None

OpenCode version

1.18.18 (bundled with OpenChamber desktop)

Steps to reproduce

1. curl.exe -X POST "https://opencode.ai/zen/go/v1/chat/completions" -H "Authorization: Bearer " -H "Content-Type: application/json" -d '{"model":"deepseek-v4-flash","messages":[{"role":"user","content":"hi"}],"stream":true}' -> HTTP 500 {"type":"error","error":{"type":"error","message":"Internal server error"}}
2. Same request without "stream":true -> HTTP 200, normal completion
3. Same request over HTTP/2 (e.g. node http2 module, or bun fetch used by the opencode CLI) -> HTTP 200, normal SSE stream

Screenshot and/or share link

No response

Operating System

Windows 11

Terminal

OpenChamber desktop (bundled opencode-cli)