Expand root authorization context to 16 messages (#47947)

## What changed

Increase `MAX_ROOT_MESSAGES` from 8 to 16 so Guardian subagent authorization reviews can include more root conversation context.

## Testing

Update authorization integration tests to exercise the larger message limit, preserve late user authorization and question context, and expect incomplete root instructions when retained user messages exceed the cap.

GitOrigin-RevId: facc55f424a4d7e29626f4161ecfe031021b30c2

codex-rs/core/src/agent/control/user_authorization.rs

@@ -34,7 +34,7 @@ use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::protocol::MultiAgentVersion;
 
-const MAX_ROOT_MESSAGES: usize = 8;
+const MAX_ROOT_MESSAGES: usize = 16;
 
 impl LocalAgentControl {
     /// Returns bounded root conversation and authorization state for a MultiAgent V2 worker.

codex-rs/core/tests/suite/guardian_subagent_authorization.rs

@@ -393,7 +393,7 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
         ]),
     )
     .await;
-    let mut question_events = (0..8)
+    let mut question_events = (0..16)
         .map(|index| {
             ev_assistant_message(
                 &format!("deployment-update-{index}"),
@@ -522,8 +522,8 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
         );
     }
     if matches!(root_context, RootContext::RetainedAtMessageLimit) {
-        // Eight retained instructions plus the later answer exceed the root projection cap.
-        root_history_items.extend((0..6).map(|index| ResponseItem::Message {
+        // Sixteen user instructions plus the later answer exceed the root projection cap.
+        root_history_items.extend((0..14).map(|index| ResponseItem::Message {
             id: Some(ResponseItemId::with_suffix("root-instruction", index)),
             role: "user".to_owned(),
             content: vec![ContentItem::InputText {
@@ -705,6 +705,7 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
         RootContext::RetainedAtMessageLimit => {
             let mut messages = vec![
                 GuardianRootMessage::RetainedContextScope,
+                GuardianRootMessage::IncompleteRootInstructions,
                 GuardianRootMessage::IncompleteAssistantContext,
             ];
             messages.push(GuardianRootMessage::User(
@@ -714,7 +715,8 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
                 ),
             ));
             messages.extend(
-                (1..6).map(|index| GuardianRootMessage::User(format!("Root instruction {index}."))),
+                (1..14)
+                    .map(|index| GuardianRootMessage::User(format!("Root instruction {index}."))),
             );
             messages.push(GuardianRootMessage::User(USER_APPROVAL.to_owned()));
             messages.extend(answer_message);
@@ -737,7 +739,7 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
                 }
                 RootAnswer::Oversized => 4,
             };
-            messages.extend((first_assistant..8).map(|index| {
+            messages.extend((first_assistant..16).map(|index| {
                 GuardianRootMessage::Assistant(format!("Deployment inspection update {index}."))
             }));
             if question_delivered {
@@ -770,7 +772,11 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
             snapshot.messages,
             snapshot.authorization_version.retained_context_complete
         ),
-        (root_thread_id, expected_messages.clone(), evidence_complete),
+        (
+            root_thread_id,
+            expected_messages.clone(),
+            evidence_complete && !matches!(root_context, RootContext::RetainedAtMessageLimit),
+        ),
     );
 
     let worker_request = worker_review_request.single_request();
@@ -784,7 +790,10 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
     if matches!(root_context, RootContext::RetainedAtMessageLimit) {
         assert!(guardian_transcript.contains("<truncated omitted_approx_tokens="));
     }
-    assert!(!guardian_transcript.contains("some root user instructions are unavailable"));
+    assert_eq!(
+        guardian_transcript.contains("some root user instructions are unavailable"),
+        matches!(root_context, RootContext::RetainedAtMessageLimit),
+    );
     assert!(guardian_transcript.contains(">>> ROOT CONVERSATION START"));
     assert!(guardian_transcript.contains("only user messages can authorize actions"));
     assert!(
@@ -1238,7 +1247,7 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
     ) {
         // Later progress evicts the question from retained storage. Its raw source must
         // still beat newer progress when selecting the context for the ordinary reply.
-        let progress = (0..8)
+        let progress = (0..16)
             .map(|index| {
                 let mut event = ev_assistant_message(
                     &format!("post-approval-progress-{index}"),
@@ -1260,7 +1269,7 @@ async fn guardian_subagent_review_preserves_late_root_user_authorization(
                 "assistant: {ROOT_QUESTION}\nuser: {ROOT_ANSWER}\n"
             )),
         ];
-        expected.extend((5..8).map(|index| {
+        expected.extend((5..16).map(|index| {
             GuardianRootMessage::Assistant(format!("Preparing deployment step {index}."))
         }));
         assert_eq!(