decolua/9router · info

HTTP/2 is required for Cursor AgentService (endpoint is h2-o

Error message

HTTP/2 is required for Cursor AgentService (endpoint is h2-only)

What it means

The Cursor MITM handler is an intentional stub: any Cursor chat request intercepted by the proxy is answered with HTTP 501 and "Cursor MITM support is coming soon." (type "not_implemented"). This is not a fault — the feature is under development and requests are never re-routed for Cursor.

Source

Thrown at open-sse/executors/cursor.js:390

      req.on("error", finish(reject));

      if (signal) {
        const onAbort = finish(() => reject(new Error("Request aborted")));
        signal.addEventListener("abort", onAbort, { once: true });
      }

      req.write(body);
      req.end();
    });
  }

  /**
   * AgentService (agent.api5.cursor.sh) is HTTP/2-only. Node's fetch/undici speaks
   * HTTP/1.1 and fails with HTTPParserError on the h2 preface — use http2 duplex.
   */
  openAgentHttp2Stream(url, headers, signal) {
    if (!http2) {
      throw new Error("HTTP/2 is required for Cursor AgentService (endpoint is h2-only)");
    }

    const urlObj = new URL(url);
    const client = http2.connect(`https://${urlObj.host}`);
    const chunkQueue = [];
    let waiting = null;
    let ended = false;
    let streamError = null;
    let req = null;

    const wake = (result) => {
      if (!waiting) return;
      const resolve = waiting;
      waiting = null;
      resolve(result);
    };

    const fail = (error) => {

View on GitHub (pinned to 90b52e06ff)

Solutions

1. Remove/disable the 9Router MITM proxy from the Cursor IDE network settings until the feature ships.
2. Route Cursor traffic outside the proxy (direct connection) so it is never intercepted.
3. Watch the changelog for Cursor MITM support, then update 9Router.
4. If re-routing is needed now, use a tool with a real handler (e.g. Kiro, Copilot, Antigravity).

if (tool === 'cursor') {
  // Cursor MITM is a 501 stub — do not route Cursor traffic through the proxy
  bypassProxyForHost('api.cursor.sh');
}

function isCursorMitmStub(res) {
  return res.status === 501 && res.headers.get('content-type')?.includes('json');
}

const res = await send(request);
if (res.status === 501) {
  // Cursor MITM not implemented — bypass the proxy for Cursor traffic
}

When it happens

Trigger: Cursor IDE sends a request through the MITM proxy, getToolForHost resolves the host to "cursor", and server.js delegates to handlers.cursor.intercept, which unconditionally returns 501.

Common situations: User enabled the 9Router MITM proxy while using the Cursor IDE, expecting model re-routing; every intercepted Cursor request gets 501 regardless of payload.

Related errors

• Machine ID is required for Cursor API
• http2 module not available
• Cursor AgentService endpoint is not configured
• Cursor AgentService request failed: ${error.message}
• ${this.provider} requires accountId in providerSpecificData

AI-assisted analysis of decolua/9router@90b52e06ff (2026-08-30). Data as JSON: /api/errors/0d656740bf5e4add. Report an issue: GitHub.