image-gen-core (#13290)

Core tool-calling for image-gen, handles requesting and receiving logic
for images using response API

codex-rs/core/src/features.rs

@@ -131,6 +131,8 @@ pub enum Feature {
     Apps,
     /// Enable plugins.
     Plugins,
+    /// Allow the model to invoke the built-in image generation tool.
+    ImageGeneration,
     /// Route apps MCP calls through the configured gateway.
     AppsMcpGateway,
     /// Allow prompting and installing missing MCP dependencies.
@@ -649,6 +651,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::ImageGeneration,
+        key: "image_generation",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::AppsMcpGateway,
         key: "apps_mcp_gateway",
@@ -868,6 +876,12 @@ mod tests {
         assert_eq!(Feature::JsRepl.default_enabled(), false);
     }
 
+    #[test]
+    fn image_generation_is_under_development() {
+        assert_eq!(Feature::ImageGeneration.stage(), Stage::UnderDevelopment);
+        assert_eq!(Feature::ImageGeneration.default_enabled(), false);
+    }
+
     #[test]
     fn collab_is_legacy_alias_for_multi_agent() {
         assert_eq!(feature_for_key("multi_agent"), Some(Feature::Collab));