Add use_agent_identity feature flag (#17385)

codex-rs/features/src/lib.rs

@@ -186,6 +186,8 @@ pub enum Feature {
     ResponsesWebsockets,
     /// Legacy rollout flag for Responses API WebSocket transport v2 experiments.
     ResponsesWebsocketsV2,
+    /// Use the agent identity registration flow for ChatGPT-authenticated sessions.
+    UseAgentIdentity,
 }
 
 impl Feature {
@@ -909,6 +911,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Removed,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::UseAgentIdentity,
+        key: "use_agent_identity",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
 ];
 
 pub fn unstable_features_warning_event(