diff --git a/backend/crates/providers/openai/src/transport/request.rs b/backend/crates/providers/openai/src/transport/request.rs
index 5af84ca78..544498696 100644
--- a/backend/crates/providers/openai/src/transport/request.rs
+++ b/backend/crates/providers/openai/src/transport/request.rs
@@ -1,9 +1,12 @@
 //! 核心 Generate operation 到 Codex Responses wire request 的严格编码。
 
+use std::io;
+
 use base64::{Engine as _, engine::general_purpose::STANDARD};
 use gateway_core::operation::GenerateRequest;
 use gateway_protocol::openai::WS_REQUEST_HEADER_RESPONSES_LITE_CLIENT_METADATA_KEY;
 use reqwest::header::{HeaderMap, HeaderName, HeaderValue};
+use serde::Serialize as _;
 use serde_json::{Map, Value};
 use sha2::{Digest, Sha256};
 
@@ -447,7 +450,8 @@ pub(crate) fn scope_turn_metadata(
             changed |= metadata.remove(*key).is_some();
         }
     }
-    if !cross_account
+    if raw.is_ascii()
+        && !cross_account
         && !changed
         && !INSTALLATION_ID_KEYS
             .iter()
@@ -460,7 +464,40 @@ pub(crate) fn scope_turn_metadata(
             metadata.insert((*key).to_owned(), Value::String(installation_id.to_owned()));
         }
     }
-    serde_json::to_string(&metadata).ok()
+    // Codex 的 turn metadata 同时承载于 HTTP header 与 WS client_metadata。
+    // 改写安装 ID 后仍须保持官方 to_ascii_json_string 的编码合同；普通
+    // to_string 会把中文工作区路径还原成 UTF-8，触发上游 WS metadata 后 Close 1000。
+    let mut bytes = Vec::new();
+    metadata
+        .serialize(&mut serde_json::Serializer::with_formatter(
+            &mut bytes,
+            AsciiTurnMetadataFormatter,
+        ))
+        .ok()?;
+    String::from_utf8(bytes).ok()
+}
+
+struct AsciiTurnMetadataFormatter;
+
+impl serde_json::ser::Formatter for AsciiTurnMetadataFormatter {
+    fn write_string_fragment<W: ?Sized + io::Write>(
+        &mut self,
+        writer: &mut W,
+        fragment: &str,
+    ) -> io::Result<()> {
+        let mut start = 0;
+        for (index, ch) in fragment.char_indices() {
+            if ch.is_ascii() {
+                continue;
+            }
+            writer.write_all(&fragment.as_bytes()[start..index])?;
+            for unit in ch.encode_utf16(&mut [0; 2]) {
+                write!(writer, "\\u{unit:04x}")?;
+            }
+            start = index + ch.len_utf8();
+        }
+        writer.write_all(&fragment.as_bytes()[start..])
+    }
 }
 
 fn replace_existing_body_string(
diff --git a/backend/crates/providers/openai/tests/provider/contract.rs b/backend/crates/providers/openai/tests/provider/contract.rs
index 3b8f09675..0b366b617 100644
--- a/backend/crates/providers/openai/tests/provider/contract.rs
+++ b/backend/crates/providers/openai/tests/provider/contract.rs
@@ -2942,6 +2942,108 @@ async fn cross_account_scope_sanitizes_only_known_turn_metadata_fields() {
     );
 }
 
+#[tokio::test]
+async fn websocket_account_scoping_preserves_ascii_turn_metadata_and_unicode_input() {
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_scope_same").await;
+    let listener = TcpListener::bind("127.0.0.1:0").await.expect("listener");
+    let base_url = format!("http://{}", listener.local_addr().expect("address"));
+    let server = tokio::spawn(async move {
+        let (socket, _) = listener.accept().await.expect("accept websocket");
+        let mut socket = accept_codex_test_websocket(socket).await;
+        let message = socket.next().await.expect("request").expect("valid frame");
+        let body: Value = serde_json::from_str(message.to_text().expect("text")).expect("JSON");
+        socket.send(Message::Text(json!({
+            "type": "response.completed",
+            "response": {"id": "resp_ascii_metadata", "model": "gpt-5.4", "status": "completed", "output": []}
+        }).to_string().into())).await.expect("complete response");
+        body
+    });
+    // Official Codex keeps embedded turn metadata ASCII even for Unicode workspaces.
+    let raw = r#"{"installation_id":"client-installation","workspaces":{"C:\\Users\\\u9879\u76ee\\\ud83d\ude80":{"label":"caf\u00e9","literal":"\\u4e2d","quoted":"\"line\n"}}}"#;
+    let input = json!([{"role": "user", "content": "中文正文 🚀"}]);
+    let payload = ProtocolPayload::json_object(
+        "openai",
+        Map::from_iter([
+            ("model".to_owned(), json!("gpt-5.4")),
+            ("input".to_owned(), input.clone()),
+            (
+                "client_metadata".to_owned(),
+                json!({"x-codex-turn-metadata": raw}),
+            ),
+        ]),
+    )
+    .expect("payload")
+    .with_context(Map::from_iter([("turn_metadata".to_owned(), json!(raw))]));
+    let mut stream = provider_with_base_url(&store, base_url)
+        .execute(
+            planned_request(
+                "openai",
+                Operation::Generate(GenerateRequest::from_protocol_payload(payload)),
+            ),
+            context_with_state_owner("req_ascii_metadata", "acct_scope_same"),
+        )
+        .await
+        .expect("provider stream");
+    while let Some(event) = stream.next().await {
+        event.expect("successful websocket response");
+    }
+    let body = server.await.expect("server");
+    let encoded = body
+        .pointer("/client_metadata/x-codex-turn-metadata")
+        .and_then(Value::as_str)
+        .expect("turn metadata");
+    assert!(encoded.is_ascii(), "embedded header JSON must remain ASCII");
+    let mut expected: Value = serde_json::from_str(raw).expect("original metadata");
+    expected["installation_id"] = body["client_metadata"]["installation_id"].clone();
+    assert_eq!(
+        serde_json::from_str::<Value>(encoded).expect("metadata JSON"),
+        expected
+    );
+    assert_eq!(body["input"], input);
+}
+
+#[tokio::test]
+async fn http_account_scoping_keeps_unicode_metadata_ascii_in_headers_and_body() {
+    for owner in ["acct_scope_same", "acct_scope_old"] {
+        let raw = r#"{"installation_id":"client-installation","workspaces":{"/tmp/\u4e2d\u6587/\ud83d\ude80":{"label":"caf\u00e9"}}}"#;
+        let request = capture_scoped_http_request(
+            "req_ascii_http",
+            "acct_scope_same",
+            owner,
+            Map::from_iter([
+                ("model".to_owned(), json!("gpt-5.4")),
+                ("input".to_owned(), json!("中文正文 🚀")),
+                ("turnMetadata".to_owned(), json!(raw)),
+                (
+                    "client_metadata".to_owned(),
+                    json!({"x-codex-turn-metadata": raw}),
+                ),
+            ]),
+            Map::from_iter([("turn_metadata".to_owned(), json!(raw))]),
+        )
+        .await;
+        let body = captured_request_body(&request);
+        let headers = captured_header_values(&request, "x-codex-turn-metadata");
+        assert_eq!(headers.len(), 1);
+        let mut expected: Value = serde_json::from_str(raw).expect("original metadata");
+        expected["installation_id"] = body["client_metadata"]["installation_id"].clone();
+        for encoded in [
+            std::str::from_utf8(&headers[0]).expect("UTF-8 header"),
+            body["turnMetadata"].as_str().expect("body turn metadata"),
+            body["client_metadata"]["x-codex-turn-metadata"]
+                .as_str()
+                .expect("client metadata"),
+        ] {
+            assert!(encoded.is_ascii(), "scoped header JSON must remain ASCII");
+            assert_eq!(
+                serde_json::from_str::<Value>(encoded).expect("metadata JSON"),
+                expected
+            );
+        }
+    }
+}
+
 #[tokio::test]
 async fn cross_account_continuation_should_require_client_replay_without_an_upstream_probe() {
     let store = Arc::new(MemoryAccountStore::default());