Preserve Guardian history across thread reconstruction (#42065)

## Why

Guardian review evidence must remain available after a compacted thread is resumed or forked, while rolled-back or parent-local evidence must not grant authorization in a different context.

## What changed

- Store the bounded, model-invisible Guardian transcript alongside compacted rollout history and restore it from the newest surviving checkpoint during replay.
- Trim Guardian history at rollback boundaries, clearing it when the boundary has already been evicted.
- Preserve the checkpoint for user-initiated forks, but remove it when spawning a subagent so parent review evidence is not inherited.
- Keep the new rollout field optional for compatibility with existing compacted records and legacy readers.

## Testing

- Cover Guardian history across compaction, restart, paginated and pathless stores, user forks, rollback, bounded replay, serialization, and subagent forks.

GitOrigin-RevId: 6ab076d5e0c3aac4d6a41ebd50ba2b200c90213e

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

@@ -996,6 +996,9 @@ impl AgentControl {
                 RolloutItem::Compacted(compacted) => {
                     // This checkpoint belongs to the inherited parent prefix.
                     compacted.latest_token_usage_record = None;
+                    // Parent-local review evidence must not become the child's authorization.
+                    // Root user authorization is collected separately by the host.
+                    compacted.guardian_history = None;
                     if let Some(replacement_history) = compacted.replacement_history.as_mut() {
                         // Matches before this checkpoint cannot survive its replacement history.
                         replaced_parent_developer_instructions = false;

codex-rs/core/src/agent/control_tests.rs

@@ -1410,6 +1410,7 @@ async fn spawn_agent_fork_drops_inherited_token_usage_state() {
             RolloutItem::Compacted(CompactedItem {
                 message: String::new(),
                 replacement_history: Some(vec![user_message("compacted parent context").into()]),
+                guardian_history: None,
                 mcp_resource_origins: None,
                 window_number: None,
                 first_window_id: None,
@@ -1525,6 +1526,7 @@ async fn spawn_agent_numeric_fork_from_compacted_paginated_parent_clamps_to_prov
                     }
                     .into(),
                 ]),
+                guardian_history: None,
                 mcp_resource_origins: None,
                 window_number: None,
                 first_window_id: None,
@@ -2023,6 +2025,9 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
                 replacement_history: Some(
                     replacement_history.into_iter().map(Into::into).collect(),
                 ),
+                guardian_history: Some(codex_history::GuardianHistoryCheckpoint(vec![
+                    user_message("Parent-local approval must not be inherited."),
+                ])),
                 mcp_resource_origins: None,
                 window_number: None,
                 first_window_id: None,
@@ -2079,6 +2084,13 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
         .await
         .expect("child thread should be registered");
     let history = child_thread.session.clone_history().await;
+    assert!(
+        !history_contains_text(
+            history.conversation_history_snapshot().review_items(),
+            "Parent-local approval must not be inherited.",
+        ),
+        "a subagent must not inherit its parent review checkpoint",
+    );
     assert!(
         history_contains_text(history.raw_items(), "compacted parent summary"),
         "forked child history should retain compacted non-hint content"
@@ -2207,6 +2219,7 @@ async fn spawn_agent_full_fork_restores_instructions_after_compaction_discards_p
                 replacement_history: Some(
                     replacement_history.into_iter().map(Into::into).collect(),
                 ),
+                guardian_history: None,
                 mcp_resource_origins: None,
                 window_number: None,
                 first_window_id: None,
@@ -2362,6 +2375,7 @@ async fn spawn_agent_full_fork_legacy_compaction_rebuilds_child_instructions_onc
             RolloutItem::Compacted(CompactedItem {
                 message: "legacy compacted summary".to_string(),
                 replacement_history: None,
+                guardian_history: None,
                 mcp_resource_origins: None,
                 window_number: None,
                 first_window_id: None,