Register the Guardian additional-context feature flag (#59238)

## What changed

Add `guardian_include_additional_context` as a stable feature enabled by default, with a corresponding `GuardianIncludeAdditionalContext` enum variant. Document its purpose as including standalone additional-context tool outputs in Guardian review history, and expose the boolean flag in the configuration schema.

GitOrigin-RevId: 505132e5916bd7b3f1d6d80c2219051912ad8271

codex-rs/core/config.schema.json

@@ -1081,6 +1081,9 @@
             "guardian_ext": {
               "type": "boolean"
             },
+            "guardian_include_additional_context": {
+              "type": "boolean"
+            },
             "guardian_native_multi_agent_history": {
               "type": "boolean"
             },
@@ -7877,6 +7880,9 @@
         "guardian_ext": {
           "type": "boolean"
         },
+        "guardian_include_additional_context": {
+          "type": "boolean"
+        },
         "guardian_native_multi_agent_history": {
           "type": "boolean"
         },

codex-rs/features/src/lib.rs

@@ -420,6 +420,8 @@ pub enum Feature {
     SendMessageToUserAsync,
     /// Enable automatic review for approval prompts.
     GuardianApproval,
+    /// Include standalone additional-context tool outputs in Guardian review history.
+    GuardianIncludeAdditionalContext,
     /// Forward private reviewer items and interruptions to raw-event observers.
     GuardianRecordedItems,
     /// Removed compatibility flag for always-on thread-owned Guardian context.
@@ -2091,6 +2093,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Stable,
         default_enabled: true,
     },
+    FeatureSpec {
+        id: Feature::GuardianIncludeAdditionalContext,
+        key: "guardian_include_additional_context",
+        stage: Stage::Stable,
+        default_enabled: true,
+    },
     FeatureSpec {
         id: Feature::GuardianRecordedItems,
         key: "guardian_recorded_items",