Improve handling of config and rules errors for app server clients (#9182)

When an invalid config.toml key or value is detected, the CLI currently
just quits. This leaves the VSCE in a dead state.

This PR changes the behavior to not quit and bubble up the config error
to users to make it actionable. It also surfaces errors related to
"rules" parsing.

This allows us to surface these errors to users in the VSCE, like this:

<img width="342" height="129" alt="Screenshot 2026-01-13 at 4 29 22 PM"
src="https://github.com/user-attachments/assets/a79ffbe7-7604-400c-a304-c5165b6eebc4"
/>

<img width="346" height="244" alt="Screenshot 2026-01-13 at 4 45 06 PM"
src="https://github.com/user-attachments/assets/de874f7c-16a2-4a95-8c6d-15f10482e67b"
/>

codex-rs/core/src/exec_policy.rs

@@ -46,19 +46,19 @@ fn is_policy_match(rule_match: &RuleMatch) -> bool {
 
 #[derive(Debug, Error)]
 pub enum ExecPolicyError {
-    #[error("failed to read execpolicy files from {dir}: {source}")]
+    #[error("failed to read rules files from {dir}: {source}")]
     ReadDir {
         dir: PathBuf,
         source: std::io::Error,
     },
 
-    #[error("failed to read execpolicy file {path}: {source}")]
+    #[error("failed to read rules file {path}: {source}")]
     ReadFile {
         path: PathBuf,
         source: std::io::Error,
     },
 
-    #[error("failed to parse execpolicy file {path}: {source}")]
+    #[error("failed to parse rules file {path}: {source}")]
     ParsePolicy {
         path: String,
         source: codex_execpolicy::Error,
@@ -67,19 +67,19 @@ pub enum ExecPolicyError {
 
 #[derive(Debug, Error)]
 pub enum ExecPolicyUpdateError {
-    #[error("failed to update execpolicy file {path}: {source}")]
+    #[error("failed to update rules file {path}: {source}")]
     AppendRule { path: PathBuf, source: AmendError },
 
-    #[error("failed to join blocking execpolicy update task: {source}")]
+    #[error("failed to join blocking rules update task: {source}")]
     JoinBlockingTask { source: tokio::task::JoinError },
 
-    #[error("failed to update in-memory execpolicy: {source}")]
+    #[error("failed to update in-memory rules: {source}")]
     AddRule {
         #[from]
         source: ExecPolicyRuleError,
     },
 
-    #[error("cannot append execpolicy rule because execpolicy feature is disabled")]
+    #[error("cannot append rule because rules feature is disabled")]
     FeatureDisabled,
 }
 
@@ -98,7 +98,11 @@ impl ExecPolicyManager {
         features: &Features,
         config_stack: &ConfigLayerStack,
     ) -> Result<Self, ExecPolicyError> {
-        let policy = load_exec_policy_for_features(features, config_stack).await?;
+        let (policy, warning) =
+            load_exec_policy_for_features_with_warning(features, config_stack).await?;
+        if let Some(err) = warning.as_ref() {
+            tracing::warn!("failed to parse rules: {err}");
+        }
         Ok(Self::new(Arc::new(policy)))
     }
 
@@ -195,14 +199,26 @@ impl Default for ExecPolicyManager {
     }
 }
 
-async fn load_exec_policy_for_features(
+pub async fn check_execpolicy_for_warnings(
     features: &Features,
     config_stack: &ConfigLayerStack,
-) -> Result<Policy, ExecPolicyError> {
+) -> Result<Option<ExecPolicyError>, ExecPolicyError> {
+    let (_, warning) = load_exec_policy_for_features_with_warning(features, config_stack).await?;
+    Ok(warning)
+}
+
+async fn load_exec_policy_for_features_with_warning(
+    features: &Features,
+    config_stack: &ConfigLayerStack,
+) -> Result<(Policy, Option<ExecPolicyError>), ExecPolicyError> {
     if !features.enabled(Feature::ExecPolicy) {
-        Ok(Policy::empty())
-    } else {
-        load_exec_policy(config_stack).await
+        return Ok((Policy::empty(), None));
+    }
+
+    match load_exec_policy(config_stack).await {
+        Ok(policy) => Ok((policy, None)),
+        Err(err @ ExecPolicyError::ParsePolicy { .. }) => Ok((Policy::empty(), Some(err))),
+        Err(err) => Err(err),
     }
 }
 
@@ -239,7 +255,7 @@ pub async fn load_exec_policy(config_stack: &ConfigLayerStack) -> Result<Policy,
     }
 
     let policy = parser.build();
-    tracing::debug!("loaded execpolicy from {} files", policy_paths.len());
+    tracing::debug!("loaded rules from {} files", policy_paths.len());
 
     Ok(policy)
 }