Preserve thread settings for goal-first and forked threads (#34469)

## Why

Goal-first and forked threads could create rollouts without recording their
effective thread settings. Resuming those threads after a restart could then
use current configuration instead of the settings selected when the thread was
created.

## What changed

- Persist a `thread_settings_applied` item when a goal first materializes a
  rollout, including a follow-up snapshot if settings changed concurrently.
- Append each fork's effective settings after its copied history so they take
  precedence over inherited settings during resume.
- Centralize conversion from `ThreadConfigSnapshot` to
  `ThreadSettingsSnapshot`.

## Testing

Added coverage that restarts the app server and verifies goal-first and forked
threads retain their respective `approvals_reviewer` settings.

GitOrigin-RevId: 6cb9aaae73bbe9ca432831cff7e826f95ffd6d01

codex-rs/core/src/codex_thread.rs

@@ -34,6 +34,7 @@ use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::Submission;
 use codex_protocol::protocol::ThreadHistoryMode;
 use codex_protocol::protocol::ThreadMemoryMode;
+use codex_protocol::protocol::ThreadSettingsSnapshot;
 use codex_protocol::protocol::ThreadSource;
 use codex_protocol::protocol::TokenUsageInfo;
 use codex_protocol::protocol::TurnEnvironmentSelection;
@@ -138,6 +139,24 @@ impl ThreadConfigSnapshot {
             self.cwd().as_path(),
         )
     }
+
+    pub fn into_thread_settings_snapshot(self) -> ThreadSettingsSnapshot {
+        let cwd = self.cwd().clone();
+        ThreadSettingsSnapshot {
+            model: self.model,
+            model_provider_id: self.model_provider_id,
+            service_tier: self.service_tier,
+            approval_policy: self.approval_policy,
+            approvals_reviewer: self.approvals_reviewer,
+            permission_profile: self.permission_profile,
+            active_permission_profile: self.active_permission_profile,
+            cwd,
+            reasoning_effort: self.reasoning_effort,
+            reasoning_summary: self.reasoning_summary,
+            personality: self.personality,
+            collaboration_mode: self.collaboration_mode,
+        }
+    }
 }
 
 /// Thread settings overrides that app-server validates before starting a turn.

codex-rs/core/src/session/handlers.rs

@@ -43,7 +43,6 @@ use codex_protocol::protocol::ThreadMemoryMode;
 use codex_protocol::protocol::ThreadRolledBackEvent;
 use codex_protocol::protocol::ThreadSettingsAppliedEvent;
 use codex_protocol::protocol::ThreadSettingsOverrides;
-use codex_protocol::protocol::ThreadSettingsSnapshot;
 use codex_protocol::protocol::TurnAbortReason;
 use codex_protocol::protocol::WarningEvent;
 use codex_protocol::request_permissions::RequestPermissionsResponse;
@@ -165,27 +164,13 @@ async fn thread_settings_update(
     }
 }
 
-async fn thread_settings_applied_event(sess: &Session) -> EventMsg {
+pub(super) async fn thread_settings_applied_event(sess: &Session) -> EventMsg {
     let snapshot = {
         let state = sess.state.lock().await;
         state.session_configuration.thread_config_snapshot()
     };
-    let cwd = snapshot.cwd().clone();
     EventMsg::ThreadSettingsApplied(ThreadSettingsAppliedEvent {
-        thread_settings: ThreadSettingsSnapshot {
-            model: snapshot.model,
-            model_provider_id: snapshot.model_provider_id,
-            service_tier: snapshot.service_tier,
-            approval_policy: snapshot.approval_policy,
-            approvals_reviewer: snapshot.approvals_reviewer,
-            permission_profile: snapshot.permission_profile,
-            active_permission_profile: snapshot.active_permission_profile,
-            cwd,
-            reasoning_effort: snapshot.reasoning_effort,
-            reasoning_summary: snapshot.reasoning_summary,
-            personality: snapshot.personality,
-            collaboration_mode: snapshot.collaboration_mode,
-        },
+        thread_settings: snapshot.into_thread_settings_snapshot(),
     })
 }
 

codex-rs/core/src/session/mod.rs

@@ -1336,9 +1336,16 @@ impl Session {
                     state.set_token_info(Some(info));
                 }
 
-                // Paginated subagents persist inherited model context while creating the live
-                // thread so the copied prefix is not observed as child-owned metadata.
-                if !rollout_items.is_empty() && !is_paginated_subagent {
+                let thread_settings_applied =
+                    RolloutItem::EventMsg(handlers::thread_settings_applied_event(self).await);
+                if is_paginated_subagent {
+                    // Paginated subagents persist inherited model context while creating the live
+                    // thread so the copied prefix is not observed as child-owned metadata.
+                    self.persist_rollout_items(&[thread_settings_applied]).await;
+                } else {
+                    // Keep the copied prefix and the child's effective settings in one append so a
+                    // cold resume cannot observe inherited settings as the child's latest value.
+                    rollout_items.push(thread_settings_applied);
                     self.persist_rollout_items(&rollout_items).await;
                 }