diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index f0d205658..440135f7f 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -78,7 +78,6 @@ use crate::client_common::ResponseEvent;
 use crate::compact::collect_user_messages;
 use crate::config::Config;
 use crate::config::Constrained;
-use crate::config::ConstraintError;
 use crate::config::ConstraintResult;
 use crate::config::GhostSnapshotConfig;
 use crate::config::types::ShellEnvironmentPolicy;
@@ -836,11 +835,8 @@ impl Session {
                 Ok(())
             }
             Err(err) => {
-                let wrapped = ConstraintError {
-                    message: format!("Could not update config: {err}"),
-                };
-                warn!(%wrapped, "rejected session settings update");
-                Err(wrapped)
+                warn!("rejected session settings update: {err}");
+                Err(err)
             }
         }
     }
@@ -861,18 +857,15 @@ impl Session {
                 }
                 Err(err) => {
                     drop(state);
-                    let wrapped = ConstraintError {
-                        message: format!("Could not update config: {err}"),
-                    };
                     self.send_event_raw(Event {
                         id: sub_id.clone(),
                         msg: EventMsg::Error(ErrorEvent {
-                            message: wrapped.to_string(),
+                            message: err.to_string(),
                             codex_error_info: Some(CodexErrorInfo::BadRequest),
                         }),
                     })
                     .await;
-                    return Err(wrapped);
+                    return Err(err);
                 }
             }
         };
diff --git a/codex-rs/core/src/config/constraint.rs b/codex-rs/core/src/config/constraint.rs
index d126b84a8..795a8d568 100644
--- a/codex-rs/core/src/config/constraint.rs
+++ b/codex-rs/core/src/config/constraint.rs
@@ -4,25 +4,25 @@ use std::sync::Arc;
 use thiserror::Error;
 
 #[derive(Debug, Error, PartialEq, Eq)]
-#[error("{message}")]
-pub struct ConstraintError {
-    pub message: String,
+pub enum ConstraintError {
+    #[error("value `{candidate}` is not in the allowed set {allowed}")]
+    InvalidValue { candidate: String, allowed: String },
+
+    #[error("field `{field_name}` cannot be empty")]
+    EmptyField { field_name: String },
 }
 
 impl ConstraintError {
     pub fn invalid_value(candidate: impl Into<String>, allowed: impl Into<String>) -> Self {
-        Self {
-            message: format!(
-                "value `{}` is not in the allowed set {}",
-                candidate.into(),
-                allowed.into()
-            ),
+        Self::InvalidValue {
+            candidate: candidate.into(),
+            allowed: allowed.into(),
         }
     }
 
     pub fn empty_field(field_name: impl Into<String>) -> Self {
-        Self {
-            message: format!("field `{}` cannot be empty", field_name.into()),
+        Self::EmptyField {
+            field_name: field_name.into(),
         }
     }
 }
diff --git a/codex-rs/tui/src/chatwidget/tests.rs b/codex-rs/tui/src/chatwidget/tests.rs
index fe96b5f97..344208f73 100644
--- a/codex-rs/tui/src/chatwidget/tests.rs
+++ b/codex-rs/tui/src/chatwidget/tests.rs
@@ -2275,12 +2275,12 @@ async fn approvals_popup_shows_disabled_presets() {
     chat.config.approval_policy =
         Constrained::new(AskForApproval::OnRequest, |candidate| match candidate {
             AskForApproval::OnRequest => Ok(()),
-            _ => Err(ConstraintError {
-                message: "this message should be printed in the description".to_string(),
-            }),
+            _ => Err(ConstraintError::invalid_value(
+                candidate.to_string(),
+                "this message should be printed in the description",
+            )),
         })
         .expect("construct constrained approval policy");
-
     chat.open_approvals_popup();
 
     let width = 80;
@@ -2311,12 +2311,12 @@ async fn approvals_popup_navigation_skips_disabled() {
     chat.config.approval_policy =
         Constrained::new(AskForApproval::OnRequest, |candidate| match candidate {
             AskForApproval::OnRequest => Ok(()),
-            _ => Err(ConstraintError {
-                message: "disabled preset".to_string(),
-            }),
+            _ => Err(ConstraintError::invalid_value(
+                candidate.to_string(),
+                "[on-request]",
+            )),
         })
         .expect("construct constrained approval policy");
-
     chat.open_approvals_popup();
 
     // The approvals popup is the active bottom-pane view; drive navigation via chat handle_key_event.