Session headers X-Session-Id, x-session-affinity, x-parent-session-id no longer sent on LLM requests: silent regression of #20744 / #31511 in the v2 session runner #42694

Summary

OpenCode used to stamp x-session-affinity, X-Session-Id and (for subagent child sessions) x-parent-session-id on every outbound LLM provider request, so proxies and gateways could correlate calls per session. That behaviour shipped in #20744 (April) and #31511 (June), and was still confirmed working by a user in late July (#39912: "I confirmed both headers reach the server").

In current releases ( i personally verified on v1.18.16 and v1.18.18) the headers are gone. No session header of any kind seems to reach the provider endpoint. The header-stamping code still exists in the repo (packages/opencode/src/session/llm/request.ts), and is even still present in the compiled release binary, but requests are now built by the v2 session runner (packages/core/src/session/runner/), which has no equivalent.

Environment

• opencode version: 1.18.16 and 1.18.18
• Mode: headless opencode serve --hostname 0.0.0.0 --port 4096, driven over the HTTP API
• OS: Debian
• Provider under test: anthropic with a custom baseURL in opencode.json (the proxy/gateway pattern the headers exist for); no special flags, OPENCODE_EXPERIMENTAL_NATIVE_LLM unset

Plugins

No response

OpenCode version

1.18.18

Steps to reproduce

1. Start a header-echo "provider" that logs request headers and answers with minimal valid Anthropic SSE:

// echo-upstream.ts — bun run echo-upstream.ts
const SSE =
  'event: message_start\ndata: {"type":"message_start","message":{"id":"m1","type":"message","role":"assistant","content":[],"model":"claude-sonnet-5","usage":{"input_tokens":1,"output_tokens":1}}}\n\n' +
  'event: content_block_start\ndata: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}\n\n' +
  'event: content_block_delta\ndata: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"ok"}}\n\n' +
  'event: content_block_stop\ndata: {"type":"content_block_stop","index":0}\n\n' +
  'event: message_delta\ndata: {"type":"message_delta","delta":{"stop_reason":"end_turn"},"usage":{"output_tokens":2}}\n\n' +
  'event: message_stop\ndata: {"type":"message_stop"}\n\n';
Bun.serve({
  port: 18099,
  fetch(req) {
    console.log(JSON.stringify({
      path: new URL(req.url).pathname,
      headerNames: [...req.headers.keys()].sort(),
      xSessionId: req.headers.get("x-session-id"),
      xSessionAffinity: req.headers.get("x-session-affinity"),
    }));
    return new Response(SSE, { status: 200, headers: { "content-type": "text/event-stream" } });
  },
});

2. Point opencode at it via ~/.config/opencode/opencode.json :

{
  "model": "anthropic/claude-sonnet-5",
  "provider": {
    "anthropic": {
      "npm": "@ai-sdk/anthropic",
      "options": { "baseURL": "http://localhost:18099/v1", "apiKey": "dummy" }
    }
  }
}

3. Run ANTHROPIC_API_KEY=dummy opencode serve --port 4096 , then drive one prompt over the API. (The per-session model pin matters: the top-level model key in opencode.json is not applied to API-created sessions, which otherwise fall through to a default provider.)

SID=$(curl -s -X POST -H "content-type: application/json" -d '{}' http://localhost:4096/session | jq -r .id)
curl -s -X POST -H "content-type: application/json" \
  -d '{"model":{"providerID":"anthropic","id":"claude-sonnet-5"}}' \
  "http://localhost:4096/api/session/$SID/model"
curl -s -X POST -H "content-type: application/json" \
  -d '{"prompt":{"text":"say ok"}}' "http://localhost:4096/api/session/$SID/prompt"

4. The echo server logs the full header set of the LLM request:

{"path":"/v1/messages",
 "headerNames":["accept","accept-encoding","anthropic-beta","anthropic-version","b3","connection","content-length","content-type","host","traceparent","user-agent","x-api-key"],
 "xSessionId":null,"xSessionAffinity":null}

The following are missing: x-session-affinity, X-Session-Id, x-parent-session-id.

Screenshot and/or share link

No response

Operating System

Debian 13 (Trixie)

Terminal

No response