Add Guardian native multi-agent history feature flag (#57441)

## What changed

Register `guardian_native_multi_agent_history` as an under-development feature,
disabled by default, and expose it in the configuration schema.

GitOrigin-RevId: d434750c1aa0cc78b36d1d661a4df0def5426f02

codex-rs/core/config.schema.json

@@ -1059,6 +1059,9 @@
             "guardian_ext": {
               "type": "boolean"
             },
+            "guardian_native_multi_agent_history": {
+              "type": "boolean"
+            },
             "guardian_node_repl_transcript_images": {
               "type": "boolean"
             },
@@ -7701,6 +7704,9 @@
         "guardian_ext": {
           "type": "boolean"
         },
+        "guardian_native_multi_agent_history": {
+          "type": "boolean"
+        },
         "guardian_node_repl_transcript_images": {
           "type": "boolean"
         },

codex-rs/features/src/lib.rs

@@ -405,6 +405,8 @@ pub enum Feature {
     GuardianReuseParentCompaction,
     /// Limit worker Guardian root evidence to preceding root communication windows.
     GuardianRootHandoffContext,
+    /// Preserve native MAv2 tool calls in synchronous Guardian history.
+    GuardianNativeMultiAgentHistory,
     /// Include completed node_repl or cua_repl Code Mode responses in Guardian reviews.
     GuardianEnhancedNodeReplTranscripts,
     /// Include completed node_repl or cua_repl Code Mode response images in Guardian reviews.
@@ -1993,6 +1995,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::GuardianNativeMultiAgentHistory,
+        key: "guardian_native_multi_agent_history",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::GuardianEnhancedNodeReplTranscripts,
         key: "guardian_enhanced_node_repl_transcripts",