[Bug] OpenCode requests lack x-opencode-session and a specific User-Agent required by the Go docs

[cabrinha]

Affected area

AI providers and models

What happened?

The OpenCode Go docs (https://opencode.ai/docs/go/#where-can-i-use-it) state that Go traffic is monitored, and that to avoid an account being flagged the client must (1) identify itself with a specific User-Agent ("no broad user agents") and (2) send the x-opencode-session header so Go can optimize prompt caching.

Prime Agent does neither for opencode / opencode-go models:

• User-Agent is the SDK default (OpenAI/JS ... on the Responses/Completions paths).
• x-opencode-session is never sent.

Impact for Go subscribers: worse prompt-cache hit rate, which burns the dollar-based Go allowance ($12 / 5h, $30 / week, $60 / month) faster, plus a risk of the account being flagged for unidentified traffic.

Reference: OpenCode's own client (anomalyco/opencode, packages/opencode/src/session/llm/request.ts) sends x-opencode-session: <sessionID> and User-Agent: opencode/<version> for every provider id starting with opencode.

Prior art in this repo: f0ebb327f fix(ai): set default Kimi Coding user agent closes #3586 set a provider-specific User-Agent via static headers for kimi-coding. The same pattern fits here, plus a dynamic x-opencode-session from the existing sessionId plumbing in createClient of openai-responses.ts, openai-completions.ts, and anthropic.ts.

Workaround today: provider headers in ~/.prime/agent/models.json with "x-opencode-session": "!uuidgen". That gives one id per process, not per session, and does not distinguish subagent sessions.

Steps to reproduce

1. Authenticate the opencode-go provider (OPENCODE_API_KEY).
2. In ~/.prime/agent/models.json, point the opencode-go provider baseUrl at a local request-capturing proxy (for example mitmproxy or nc -l 8080) that forwards to https://opencode.ai/zen/go/v1.
3. Start prime-agent, select opencode-go/muse-spark-1.3-contributor (Responses API) and send a prompt.
4. Inspect the captured request headers.
5. Repeat with opencode-go/deepseek-v4-flash (Completions API) and opencode-go/minimax-m3 (Anthropic Messages API).

Expected behavior

For every request to an opencode or opencode-go model, on all three API paths:

• x-opencode-session: <prime-agent session id> (the same id already used for session_id / prompt_cache_key), distinct per session including RLM subagent sessions.
• A specific User-Agent, e.g. prime-agent/<version>, instead of the SDK default.

Headers need not be added for non-OpenCode providers.

Prime Agent version

0.9.2

Installation method

Stable release installer

Operating system

macOS

Operating system version

macOS 26.6.2

CPU architecture

arm64 / aarch64

Shell and terminal

zsh, ghostty

Additional context

No response

[inxeoz]

i am using a custom plugin to workaround this issue for now

https://github.com/inxeoz/prime-agent-ext/blob/master/x-opencode-session.ts

[kevinjosethomas]

I’m taking a look at this.

[kevinjosethomas]

Merged in #2131; this fix is not released yet.