test(openai): merge websocket proxy header regression (#67)

Preserve the original contributor commit and its two-frame Cloudflare header regression. Resolve overlap with the existing transport-header fix while keeping the identity-encoding fixture and ingress decompression documentation from main.

Validation: 385 API, protocol, and application tests, Rustfmt, and strict workspace Clippy passed. The new regression also passed independently. No new live Cloudflare/OpenAI end-to-end run was performed.

Co-authored-by: Codex <noreply@openai.com>

backend/crates/gateway-api/tests/openai/responses/websocket/protocol.rs

@@ -1,8 +1,53 @@
+use axum::http::{HeaderMap, HeaderValue};
+use base64::{Engine as _, engine::general_purpose::STANDARD};
+use gateway_api::openai::responses::{OpenAiRequestHeaders, decode_response_create_with_context};
 use gateway_core::operation::Operation;
 use serde_json::json;
 
 use super::decode_response_create;
 
+#[test]
+fn response_create_should_exclude_cloudflare_headers_on_every_frame() {
+    let mut headers = HeaderMap::new();
+    for (name, value) in [
+        ("CF-Visitor", r#"{"scheme":"https"}"#),
+        ("cdn-loop", "cloudflare; loops=1"),
+        ("cf-warp-tag-id", "downstream-warp"),
+        ("cf-ipcountry", "US"),
+        ("cf-worker", "worker.example"),
+        ("cf-ew-via", "15"),
+        ("cf-future-proxy-field", "downstream-only"),
+    ] {
+        headers.insert(name, HeaderValue::from_static(value));
+    }
+    headers.append("x-openai-future-mode", HeaderValue::from_static("first"));
+    headers.append("x-openai-future-mode", HeaderValue::from_static("second"));
+    let request_headers = OpenAiRequestHeaders::from_headers(&headers);
+
+    // 连接级头会用于同一 WebSocket 的每一帧，后续帧也不能恢复下游链路元数据。
+    for input in ["hello", "continue"] {
+        let decoded = decode_response_create_with_context(
+            &json!({"type": "response.create", "model": "smart-code", "input": input}).to_string(),
+            &request_headers,
+        )
+        .expect("decode response.create behind Cloudflare");
+        let Operation::Generate(request) = decoded.operation() else {
+            panic!("Responses must map to Generate");
+        };
+        assert_eq!(
+            request
+                .protocol_payload()
+                .context()
+                .get("opaque_request_headers"),
+            Some(&json!([
+                ["x-openai-future-mode", STANDARD.encode(b"first")],
+                ["x-openai-future-mode", STANDARD.encode(b"second")],
+            ])),
+        );
+        assert_eq!(request.protocol_payload().body()["input"], input);
+    }
+}
+
 #[test]
 fn latest_official_codex_response_create_fixture_decodes_unchanged() {
     // Audited against openai/codex main 94cbbddafc1776d5e377bca1b05932c697e82238.