Configure Guardian sampling for responses lite (#38527)

## What changed

- Opt Guardian V2 Luna sampler WebSocket connections into responses lite.
- Send `reasoning.context` as `all_turns` on sampling requests.

## Testing

- Extend sampler and extension tests to verify the connection header and reasoning context.

GitOrigin-RevId: 4b0263c01b8259ed5268c222dcf7559912baba8c

codex-rs/ext/guardian-v2/src/extension_tests.rs

@@ -147,6 +147,7 @@ async fn contributor_samples_tool_calls_with_the_existing_luna_pool() -> Result<
     assert_eq!(request["client_metadata"]["thread_id"], "thread-1");
     assert_eq!(request["client_metadata"]["turn_id"], "turn-1");
     assert_eq!(request["reasoning"]["effort"], "low");
+    assert_eq!(request["reasoning"]["context"], "all_turns");
     assert_eq!(request["text"]["format"]["strict"], true);
     assert_eq!(
         request["text"]["format"]["schema"]["properties"]["scores"]["properties"]["action_risk"],

codex-rs/ext/guardian-v2/src/sampler.rs

@@ -6,6 +6,7 @@ use std::time::Instant;
 
 use codex_api::ApiError;
 use codex_api::Reasoning;
+use codex_api::ReasoningContext;
 use codex_api::ResponseEvent;
 use codex_api::ResponsesApiRequest;
 use codex_api::ResponsesWebsocketClient;
@@ -171,6 +172,10 @@ impl LunaSampler {
             "openai-beta",
             HeaderValue::from_static(RESPONSES_WEBSOCKETS_BETA),
         );
+        headers.insert(
+            "x-openai-internal-codex-responses-lite",
+            HeaderValue::from_static("true"),
+        );
         if let Some(originator) = self.config.originator.as_deref() {
             add_originator_header(&mut headers, originator);
         }
@@ -292,7 +297,7 @@ impl LunaSampler {
             reasoning: Some(Reasoning {
                 effort: Some(request.reasoning_effort),
                 summary: None,
-                context: None,
+                context: Some(ReasoningContext::AllTurns),
             }),
             store: false,
             stream: true,

codex-rs/ext/guardian-v2/src/sampler_tests.rs

@@ -131,6 +131,10 @@ async fn preconnected_sampler_reuses_authenticated_websocket_for_structured_requ
         handshake.header("OpenAI-Beta"),
         Some("responses_websockets=2026-02-06".to_owned())
     );
+    assert_eq!(
+        handshake.header("x-openai-internal-codex-responses-lite"),
+        Some("true".to_owned())
+    );
     assert_eq!(handshake.header("session-id"), Some("session-1".to_owned()));
     assert_eq!(handshake.header("thread-id"), Some("thread-1".to_owned()));
     assert_eq!(
@@ -196,6 +200,7 @@ async fn preconnected_sampler_reuses_authenticated_websocket_for_structured_requ
         assert!(request.get("tools").is_none());
         let effort = if index == 0 { "none" } else { "medium" };
         assert_eq!(request["reasoning"]["effort"], effort);
+        assert_eq!(request["reasoning"]["context"], "all_turns");
         assert_eq!(
             request["client_metadata"]["turn_id"],
             format!("turn-{}", index + 1)