Add hierarchical agent prompt (#8996)

codex-rs/core/src/features.rs

@@ -86,6 +86,8 @@ pub enum Feature {
     RemoteModels,
     /// Experimental shell snapshotting.
     ShellSnapshot,
+    /// Append additional AGENTS.md guidance to user instructions.
+    HierarchicalAgents,
     /// Experimental TUI v2 (viewport) implementation.
     Tui2,
     /// Enforce UTF8 output in Powershell.
@@ -352,6 +354,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         },
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::HierarchicalAgents,
+        key: "hierarchical_agents",
+        stage: Stage::Experimental,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::ApplyPatchFreeform,
         key: "apply_patch_freeform",