default enable compression, update test helpers (#10102)

set `enable_request_compression` flag to default-enabled.

update integration test helpers to decompress `zstd` if flag set.

codex-rs/core/tests/common/responses.rs

@@ -76,9 +76,32 @@ impl ResponseMock {
 #[derive(Debug, Clone)]
 pub struct ResponsesRequest(wiremock::Request);
 
+fn is_zstd_encoding(value: &str) -> bool {
+    value
+        .split(',')
+        .any(|entry| entry.trim().eq_ignore_ascii_case("zstd"))
+}
+
+fn decode_body_bytes(body: &[u8], content_encoding: Option<&str>) -> Vec<u8> {
+    if content_encoding.is_some_and(is_zstd_encoding) {
+        zstd::stream::decode_all(std::io::Cursor::new(body)).unwrap_or_else(|err| {
+            panic!("failed to decode zstd request body: {err}");
+        })
+    } else {
+        body.to_vec()
+    }
+}
+
 impl ResponsesRequest {
     pub fn body_json(&self) -> Value {
-        self.0.body_json().unwrap()
+        let body = decode_body_bytes(
+            &self.0.body,
+            self.0
+                .headers
+                .get("content-encoding")
+                .and_then(|value| value.to_str().ok()),
+        );
+        serde_json::from_slice(&body).unwrap()
     }
 
     pub fn body_bytes(&self) -> Vec<u8> {
@@ -105,7 +128,7 @@ impl ResponsesRequest {
     }
 
     pub fn input(&self) -> Vec<Value> {
-        self.0.body_json::<Value>().unwrap()["input"]
+        self.body_json()["input"]
             .as_array()
             .expect("input array not found in request")
             .clone()
@@ -1083,7 +1106,14 @@ fn validate_request_body_invariants(request: &wiremock::Request) {
     if request.method != "POST" || !request.url.path().ends_with("/responses") {
         return;
     }
-    let Ok(body): Result<Value, _> = request.body_json() else {
+    let body_bytes = decode_body_bytes(
+        &request.body,
+        request
+            .headers
+            .get("content-encoding")
+            .and_then(|value| value.to_str().ok()),
+    );
+    let Ok(body): Result<Value, _> = serde_json::from_slice(&body_bytes) else {
         return;
     };
     let Some(items) = body.get("input").and_then(Value::as_array) else {