Gemini API key leaks via reqwest error messages returned to proxy users

[iBreaker]

Problem

The Gemini adapter embeds the API key directly in the URL query parameter (?key=...) at crates/nyro-core/src/proxy/adapter.rs:92-98:

fn build_url(&self, base_url: &str, path: &str, api_key: &str) -> String {
    let url = format!("{}{path}", base_url.trim_end_matches('/'));
    if url.contains('?') {
        format!("{url}&key={api_key}")
    } else {
        format!("{url}?key={api_key}")
    }
}

When reqwest encounters a connection error, timeout, or DNS failure, its Error Display implementation includes the full request URL. The handler then returns this error to the proxy user via error_response(502, &format!("upstream error: {e}")) (handler.rs lines 764, 907, 1081), leaking the complete Gemini API key.

Exploit scenario

1. A proxy user sends a request routed to a Gemini provider
2. The Gemini API is temporarily unreachable (DNS failure, timeout, etc.)
3. reqwest returns an error like: error sending request for url (https://generativelanguage.googleapis.com/...?key=AIzaSy...)
4. The full API key is returned to the proxy user in the 502 response

Recommendation

Sanitize error messages before returning to proxy users — strip or redact URLs containing credentials. Alternatively, avoid embedding the key in the URL and use a header-based auth approach for Gemini if supported.