feat: Constrain values for approval_policy (#7778)

Constrain `approval_policy` through new `admin_policy` config.

This PR will:
1. Add a `admin_policy` section to config, with a single field (for now)
`allowed_approval_policies`. This list constrains the set of
user-settable `approval_policy`s.
2. Introduce a new `Constrained<T>` type, which combines a current value
and a validator function. The validator function ensures disallowed
values are not set.
3. Change the type of `approval_policy` on `Config` and
`SessionConfiguration` from `AskForApproval` to
`Constrained<AskForApproval>`. The validator function is set by the
values passed into `allowed_approval_policies`.
4. `GenericDisplayRow`: add a `disabled_reason: Option<String>`. When
set, it disables selection of the value and indicates as such in the
menu. This also makes it unselectable with arrow keys or numbers. This
is used in the `/approvals` menu.

Follow ups are:
1. Do the same thing to `sandbox_policy`.
2. Propagate the allowed set of values through app-server for the
extension (though already this should prevent app-server from setting
this values, it's just that we want to disable UI elements that are
unsettable).

Happy to split this PR up if you prefer, into the logical numbered areas
above. Especially if there are parts we want to gavel on separately
(e.g. admin_policy).

Disabled full access:
<img width="1680" height="380" alt="image"
src="https://github.com/user-attachments/assets/1fb61c8c-1fcb-4dc4-8355-2293edb52ba0"
/>

Disabled `--yolo` on startup:
<img width="749" height="76" alt="image"
src="https://github.com/user-attachments/assets/0a1211a0-6eb1-40d6-a1d7-439c41e94ddb"
/>

CODEX-4087

codex-rs/core/src/config/constraint.rs

@@ -0,0 +1,195 @@
+use std::fmt;
+use std::sync::Arc;
+
+use thiserror::Error;
+
+#[derive(Debug, Error, PartialEq, Eq)]
+#[error("{message}")]
+pub struct ConstraintError {
+    pub message: 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()
+            ),
+        }
+    }
+}
+
+pub type ConstraintResult<T> = Result<T, ConstraintError>;
+
+impl From<ConstraintError> for std::io::Error {
+    fn from(err: ConstraintError) -> Self {
+        std::io::Error::new(std::io::ErrorKind::InvalidInput, err)
+    }
+}
+
+type ConstraintValidator<T> = dyn Fn(&T) -> ConstraintResult<()> + Send + Sync;
+
+#[derive(Clone)]
+pub struct Constrained<T> {
+    value: T,
+    validator: Arc<ConstraintValidator<T>>,
+}
+
+impl<T: Send + Sync> Constrained<T> {
+    pub fn new(
+        initial_value: T,
+        validator: impl Fn(&T) -> ConstraintResult<()> + Send + Sync + 'static,
+    ) -> ConstraintResult<Self> {
+        let validator: Arc<ConstraintValidator<T>> = Arc::new(validator);
+        validator(&initial_value)?;
+        Ok(Self {
+            value: initial_value,
+            validator,
+        })
+    }
+
+    pub fn allow_any(initial_value: T) -> Self {
+        Self {
+            value: initial_value,
+            validator: Arc::new(|_| Ok(())),
+        }
+    }
+
+    pub fn allow_values(initial_value: T, allowed: Vec<T>) -> ConstraintResult<Self>
+    where
+        T: PartialEq + Send + Sync + fmt::Debug + 'static,
+    {
+        Self::new(initial_value, move |candidate| {
+            if allowed.contains(candidate) {
+                Ok(())
+            } else {
+                Err(ConstraintError::invalid_value(
+                    format!("{candidate:?}"),
+                    format!("{allowed:?}"),
+                ))
+            }
+        })
+    }
+
+    pub fn get(&self) -> &T {
+        &self.value
+    }
+
+    pub fn value(&self) -> T
+    where
+        T: Copy,
+    {
+        self.value
+    }
+
+    pub fn can_set(&self, candidate: &T) -> ConstraintResult<()> {
+        (self.validator)(candidate)
+    }
+
+    pub fn set(&mut self, value: T) -> ConstraintResult<()> {
+        (self.validator)(&value)?;
+        self.value = value;
+        Ok(())
+    }
+}
+
+impl<T> std::ops::Deref for Constrained<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.value
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for Constrained<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Constrained")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+impl<T: PartialEq> PartialEq for Constrained<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.value == other.value
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn constrained_allow_any_accepts_any_value() {
+        let mut constrained = Constrained::allow_any(5);
+        constrained.set(-10).expect("allow any accepts all values");
+        assert_eq!(constrained.value(), -10);
+    }
+
+    #[test]
+    fn constrained_new_rejects_invalid_initial_value() {
+        let result = Constrained::new(0, |value| {
+            if *value > 0 {
+                Ok(())
+            } else {
+                Err(ConstraintError::invalid_value(
+                    value.to_string(),
+                    "positive values",
+                ))
+            }
+        });
+
+        assert_eq!(
+            result,
+            Err(ConstraintError::invalid_value("0", "positive values"))
+        );
+    }
+
+    #[test]
+    fn constrained_set_rejects_invalid_value_and_leaves_previous() {
+        let mut constrained = Constrained::new(1, |value| {
+            if *value > 0 {
+                Ok(())
+            } else {
+                Err(ConstraintError::invalid_value(
+                    value.to_string(),
+                    "positive values",
+                ))
+            }
+        })
+        .expect("initial value should be accepted");
+
+        let err = constrained
+            .set(-5)
+            .expect_err("negative values should be rejected");
+        assert_eq!(err, ConstraintError::invalid_value("-5", "positive values"));
+        assert_eq!(constrained.value(), 1);
+    }
+
+    #[test]
+    fn constrained_can_set_allows_probe_without_setting() {
+        let constrained = Constrained::new(1, |value| {
+            if *value > 0 {
+                Ok(())
+            } else {
+                Err(ConstraintError::invalid_value(
+                    value.to_string(),
+                    "positive values",
+                ))
+            }
+        })
+        .expect("initial value should be accepted");
+
+        constrained
+            .can_set(&2)
+            .expect("can_set should accept positive value");
+        let err = constrained
+            .can_set(&-1)
+            .expect_err("can_set should reject negative value");
+        assert_eq!(err, ConstraintError::invalid_value("-1", "positive values"));
+        assert_eq!(constrained.value(), 1);
+    }
+}

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

@@ -54,10 +54,14 @@ use crate::config::profile::ConfigProfile;
 use toml::Value as TomlValue;
 use toml_edit::DocumentMut;
 
+mod constraint;
 pub mod edit;
 pub mod profile;
 pub mod service;
 pub mod types;
+pub use constraint::Constrained;
+pub use constraint::ConstraintError;
+pub use constraint::ConstraintResult;
 
 pub use service::ConfigService;
 pub use service::ConfigServiceError;
@@ -106,7 +110,7 @@ pub struct Config {
     pub model_provider: ModelProviderInfo,
 
     /// Approval policy for executing commands.
-    pub approval_policy: AskForApproval,
+    pub approval_policy: Constrained<AskForApproval>,
 
     pub sandbox_policy: SandboxPolicy,
 
@@ -1026,15 +1030,14 @@ impl Config {
             .or(cfg.approval_policy)
             .unwrap_or_else(|| {
                 if active_project.is_trusted() {
-                    // If no explicit approval policy is set, but we trust cwd, default to OnRequest
                     AskForApproval::OnRequest
                 } else if active_project.is_untrusted() {
-                    // If project is explicitly marked untrusted, require approval for non-safe commands
                     AskForApproval::UnlessTrusted
                 } else {
                     AskForApproval::default()
                 }
             });
+        let approval_policy = Constrained::allow_any(approval_policy);
         let did_user_set_custom_approval_policy_or_sandbox_mode = approval_policy_override
             .is_some()
             || config_profile.approval_policy.is_some()
@@ -2945,7 +2948,7 @@ model_verbosity = "high"
                 model_auto_compact_token_limit: None,
                 model_provider_id: "openai".to_string(),
                 model_provider: fixture.openai_provider.clone(),
-                approval_policy: AskForApproval::Never,
+                approval_policy: Constrained::allow_any(AskForApproval::Never),
                 sandbox_policy: SandboxPolicy::new_read_only_policy(),
                 did_user_set_custom_approval_policy_or_sandbox_mode: true,
                 forced_auto_mode_downgraded_on_windows: false,
@@ -3020,7 +3023,7 @@ model_verbosity = "high"
             model_auto_compact_token_limit: None,
             model_provider_id: "openai-chat-completions".to_string(),
             model_provider: fixture.openai_chat_completions_provider.clone(),
-            approval_policy: AskForApproval::UnlessTrusted,
+            approval_policy: Constrained::allow_any(AskForApproval::UnlessTrusted),
             sandbox_policy: SandboxPolicy::new_read_only_policy(),
             did_user_set_custom_approval_policy_or_sandbox_mode: true,
             forced_auto_mode_downgraded_on_windows: false,
@@ -3110,7 +3113,7 @@ model_verbosity = "high"
             model_auto_compact_token_limit: None,
             model_provider_id: "openai".to_string(),
             model_provider: fixture.openai_provider.clone(),
-            approval_policy: AskForApproval::OnFailure,
+            approval_policy: Constrained::allow_any(AskForApproval::OnFailure),
             sandbox_policy: SandboxPolicy::new_read_only_policy(),
             did_user_set_custom_approval_policy_or_sandbox_mode: true,
             forced_auto_mode_downgraded_on_windows: false,
@@ -3186,7 +3189,7 @@ model_verbosity = "high"
             model_auto_compact_token_limit: None,
             model_provider_id: "openai".to_string(),
             model_provider: fixture.openai_provider.clone(),
-            approval_policy: AskForApproval::OnFailure,
+            approval_policy: Constrained::allow_any(AskForApproval::OnFailure),
             sandbox_policy: SandboxPolicy::new_read_only_policy(),
             did_user_set_custom_approval_policy_or_sandbox_mode: true,
             forced_auto_mode_downgraded_on_windows: false,
@@ -3500,26 +3503,21 @@ trust_level = "untrusted"
     }
 
     #[test]
-    fn test_untrusted_project_gets_unless_trusted_approval_policy() -> std::io::Result<()> {
+    fn test_untrusted_project_gets_unless_trusted_approval_policy() -> anyhow::Result<()> {
         let codex_home = TempDir::new()?;
         let test_project_dir = TempDir::new()?;
         let test_path = test_project_dir.path();
 
-        let mut projects = std::collections::HashMap::new();
-        projects.insert(
-            test_path.to_string_lossy().to_string(),
-            ProjectConfig {
-                trust_level: Some(TrustLevel::Untrusted),
-            },
-        );
-
-        let cfg = ConfigToml {
-            projects: Some(projects),
-            ..Default::default()
-        };
-
         let config = Config::load_from_base_config_with_overrides(
-            cfg,
+            ConfigToml {
+                projects: Some(HashMap::from([(
+                    test_path.to_string_lossy().to_string(),
+                    ProjectConfig {
+                        trust_level: Some(TrustLevel::Untrusted),
+                    },
+                )])),
+                ..Default::default()
+            },
             ConfigOverrides {
                 cwd: Some(test_path.to_path_buf()),
                 ..Default::default()
@@ -3529,7 +3527,7 @@ trust_level = "untrusted"
 
         // Verify that untrusted projects get UnlessTrusted approval policy
         assert_eq!(
-            config.approval_policy,
+            config.approval_policy.value(),
             AskForApproval::UnlessTrusted,
             "Expected UnlessTrusted approval policy for untrusted project"
         );