OpenCode Zen model_id strip proxy + SessionStart hook for Grok Build (mise shim)

A developer has created a local proxy for OpenCode Zen that strips the non-standard `model_id` field from Grok CLI assistant history before forwarding requests to the upstream Chat Completions API. The proxy, written in Bun, sanitizes JSON bodies for `/chat/completions`, `/responses`, and `/messages` endpoints, ensuring compatibility with OpenCode Zen's API.

| / | | OpenCode Zen 向けローカルプロキシ | | | | Grok CLI が assistant 履歴に付ける非標準フィールド model id を | | Chat Completions 送信前に削除してから upstream へ転送する | | | | 起動: bun ~/.grok/proxies/opencode-strip-model-id/proxy.ts | | 設定: base url = "http://127.0.0.1:8787/v1" | | / | | | | const LISTEN HOST = process.env.PROXY HOST ?? "127.0.0.1" | | const LISTEN PORT = Number process.env.PROXY PORT ?? "8787" | | const UPSTREAM ORIGIN = | | process.env.OPENCODE UPSTREAM ?? "https://opencode.ai/zen" | | .replace /\/$/, "" | | const LOG = process.env.PROXY LOG === "1" | | | | type JsonObject = Record<string, unknown | | | | function isObject value: unknown : value is JsonObject { | | return value = null && typeof value === "object" && Array.isArray value | | } | | | | / messages / input 配列内の model id を削除する / | | function stripModelIdFromMessages messages: unknown : { | | stripped: number | | value: unknown | | } { | | if Array.isArray messages { | | return { stripped: 0, value: messages } | | } | | | | let stripped = 0 | | const next = messages.map message = { | | if isObject message || "model id" in message { | | return message | | } | | stripped += 1 | | const { model id: modelId, ...rest } = message | | return rest | | } | | return { stripped, value: next } | | } | | | | / Chat Completions / Responses など JSON body から model id を除去 / | | function sanitizeRequestBody bodyText: string : { | | body: string | | stripped: number | | } { | | if bodyText.trim === "" { | | return { body: bodyText, stripped: 0 } | | } | | | | let parsed: unknown | | try { | | parsed = JSON.parse bodyText | | } catch { | | return { body: bodyText, stripped: 0 } | | } | | | | if isObject parsed { | | return { body: bodyText, stripped: 0 } | | } | | | | let stripped = 0 | | | | if "messages" in parsed { | | const result = stripModelIdFromMessages parsed.messages | | parsed.messages = result.value | | stripped += result.stripped | | } | | | | // Responses API 互換 将来用 | | if "input" in parsed { | | const result = stripModelIdFromMessages parsed.input | | parsed.input = result.value | | stripped += result.stripped | | } | | | | if stripped === 0 { | | return { body: bodyText, stripped: 0 } | | } | | | | return { body: JSON.stringify parsed , stripped } | | } | | | | function hopByHopHeaders : Set<string { | | return new Set | | "connection", | | "keep-alive", | | "proxy-authenticate", | | "proxy-authorization", | | "te", | | "trailers", | | "transfer-encoding", | | "upgrade", | | "host", | | "content-length", | | | | } | | | | function copyRequestHeaders req: Request : Headers { | | const headers = new Headers | | const skip = hopByHopHeaders | | req.headers.forEach value, key = { | | if skip.has key.toLowerCase { | | return | | } | | headers.set key, value | | } | | return headers | | } | | | | function copyResponseHeaders upstream: Response : Headers { | | const headers = new Headers | | const skip = hopByHopHeaders | | upstream.headers.forEach value, key = { | | if skip.has key.toLowerCase { | | return | | } | | headers.set key, value | | } | | return headers | | } | | | | function log ...args: unknown : void { | | if LOG { | | console.log new Date .toISOString , ...args | | } | | } | | | | const server = Bun.serve { | | hostname: LISTEN HOST, | | port: LISTEN PORT, | | idleTimeout: 255, | | | | async fetch req: Request : Promise<Response { | | const url = new URL req.url | | const targetUrl = ${UPSTREAM ORIGIN}${url.pathname}${url.search} | | const method = req.method.toUpperCase | | | | try { | | const requestHeaders = copyRequestHeaders req | | let body: string | Uint8Array | undefined | | let stripped = 0 | | | | if method == "GET" && method == "HEAD" { | | const raw = await req.text | | const shouldSanitize = | | url.pathname.includes "/chat/completions" || | | url.pathname.includes "/responses" || | | url.pathname.endsWith "/messages" | | | | if shouldSanitize && raw == "" { | | const sanitized = sanitizeRequestBody raw | | body = sanitized.body | | stripped = sanitized.stripped | | if stripped 0 { | | requestHeaders.set | | "content-type", | | requestHeaders.get "content-type" ?? "application/json" | | | | } | | } else { | | body = raw | | } | | } | | | | log | | method, | | url.pathname, | | stripped 0 ? stripped model id=${stripped} : "passthrough" | | | | | | const upstream = await fetch targetUrl, { | | method, | | headers: requestHeaders, | | body, | | // @ts-expect-error Bun は duplex を受け付ける | | duplex: "half", | | } | | | | // ストリームはそのままパイプ SSE / chat streaming | | return new Response upstream.body, { | | status: upstream.status, | | statusText: upstream.statusText, | | headers: copyResponseHeaders upstream , | | } | | } catch error { | | const message = error instanceof Error ? error.message : String error | | console.error " proxy upstream error:", message | | return new Response | | JSON.stringify { | | error: { | | message: proxy upstream failed: ${message} , | | type: "proxy error", | | }, | | } , | | { | | status: 502, | | headers: { "content-type": "application/json" }, | | } | | | | } | | }, | | } | | | | console.log | | opencode-strip-model-id listening on http://${server.hostname}:${server.port} | | | | console.log opencode-strip-model-id upstream ${UPSTREAM ORIGIN} | | console.log | | opencode-strip-model-id set base url = "http://${server.hostname}:${server.port}/v1" | | | | console.log opencode-strip-model-id debug log: PROXY LOG=1 |