chore(core) rm AskForApproval::OnFailure (#28418)

## Summary
Deletes the OnFailure variant of the `AskForApproval` enum. This option
has been deprecated since #11631.

## Testing
- [x] Tests pass

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

@@ -2246,8 +2246,7 @@ impl Session {
                     strict_auto_review: false,
                 });
             }
-            AskForApproval::OnFailure
-            | AskForApproval::OnRequest
+            AskForApproval::OnRequest
             | AskForApproval::UnlessTrusted
             | AskForApproval::Granular(_) => {}
         }

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

@@ -748,15 +748,6 @@ impl Session {
             ) {
                 post_session_configured_events.push(event);
             }
-            if config.permissions.approval_policy.value() == AskForApproval::OnFailure {
-                post_session_configured_events.push(Event {
-                    id: "".to_owned(),
-                    msg: EventMsg::Warning(WarningEvent {
-                        message: "`on-failure` approval policy is deprecated and will be removed in a future release. Use `on-request` for interactive approvals or `never` for non-interactive runs.".to_string(),
-                    }),
-                });
-            }
-
             let auth = auth.as_ref();
             let auth_mode = auth.map(CodexAuth::auth_mode).map(TelemetryAuthMode::from);
             let account_id = auth.and_then(CodexAuth::get_account_id);

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

@@ -1288,7 +1288,7 @@ async fn reload_user_config_layer_updates_base_and_selected_profile_layers() {
     let profile_config_path = codex_home.join("work.config.toml");
     std::fs::write(
         &base_config_path,
-        "model = \"base\"\napproval_policy = \"on-failure\"\n",
+        "model = \"base\"\napproval_policy = \"on-request\"\n",
     )
     .expect("write base user config");
     std::fs::write(&profile_config_path, "model = \"profile-old\"\n")
@@ -10147,7 +10147,7 @@ async fn rejects_escalated_permissions_when_policy_not_on_request() {
     // Ensure policy is NOT OnRequest so the early rejection path triggers
     turn_context_raw
         .approval_policy
-        .set(AskForApproval::OnFailure)
+        .set(AskForApproval::Never)
         .expect("test setup should allow updating approval policy");
     let session = Arc::new(session);
     let mut turn_context = Arc::new(turn_context_raw);
@@ -10310,7 +10310,7 @@ async fn unified_exec_rejects_escalated_permissions_when_policy_not_on_request()
     let (session, mut turn_context_raw) = make_session_and_context().await;
     turn_context_raw
         .approval_policy
-        .set(AskForApproval::OnFailure)
+        .set(AskForApproval::Never)
         .expect("test setup should allow updating approval policy");
     let session = Arc::new(session);
     let turn_context = Arc::new(turn_context_raw);

codex-rs/core/src/session/tests/guardian_tests.rs

@@ -407,7 +407,7 @@ async fn strict_auto_review_turn_grant_forces_guardian_for_shell_command_policy_
 
     turn_context_raw
         .approval_policy
-        .set(AskForApproval::OnFailure)
+        .set(AskForApproval::Never)
         .expect("test setup should allow updating approval policy");
     turn_context_raw.permission_profile = codex_protocol::models::PermissionProfile::Disabled;
     let mut config = (*turn_context_raw.config).clone();