Retire the unused Guardian extension prototype API (#45679)

## What changed

- Mark `guardian_ext` as a removed compatibility flag.
- Remove `InternalSessionSpawner`, `InternalSessionSpawnFuture`, `ApprovalReviewInput`, and `ApprovalReviewError` from the extension API, along with the spawner test.
- Remove `NodeReplReviewEvidence::review_inputs` and make the core re-exports of `NodeReplReviewEvidenceMode` crate-private.

GitOrigin-RevId: 1c532bc57264644cf521ef8077285a9b8ed67391

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

@@ -98,7 +98,7 @@ pub(crate) use multi_agent_role_instructions::MultiAgentRoleInstructions;
 pub(crate) use multi_agent_usage_hint::MultiAgentUsageHint;
 pub(crate) use network_rule_saved::NetworkRuleSaved;
 pub use node_repl_review_evidence::NodeReplReviewEvidence;
-pub use node_repl_review_evidence::NodeReplReviewEvidenceMode;
+pub(crate) use node_repl_review_evidence::NodeReplReviewEvidenceMode;
 pub(crate) use node_repl_review_evidence::node_repl_review_evidence_mode;
 pub use permissions_instructions::ApprovalPromptContext;
 pub use permissions_instructions::PermissionsInstructions;

codex-rs/core/src/context/node_repl_review_evidence.rs

@@ -10,7 +10,7 @@ use std::sync::PoisonError;
 use codex_features::Feature;
 use codex_guardian_context::NodeReplContext;
 use codex_guardian_context::NodeReplResponse;
-pub use codex_guardian_context::NodeReplReviewEvidenceMode;
+pub(crate) use codex_guardian_context::NodeReplReviewEvidenceMode;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ImageReference;
 use codex_protocol::user_input::UserInput;
@@ -129,16 +129,6 @@ impl NodeReplReviewEvidence {
             .collect()
     }
 
-    /// Returns bounded REPL evidence using the existing Guardian text and image layout.
-    pub fn review_inputs(&self, mode: NodeReplReviewEvidenceMode) -> Vec<UserInput> {
-        if mode == NodeReplReviewEvidenceMode::Disabled {
-            return Vec::new();
-        }
-        self.snapshot_since(/*reviewed_sequence*/ 0)
-            .map(|snapshot| snapshot.context(mode).render_inputs())
-            .unwrap_or_default()
-    }
-
     pub(crate) fn record(
         &self,
         tool_name: &str,

codex-rs/ext/extension-api/src/capabilities/internal_session.rs

@@ -1,40 +0,0 @@
-use std::future::Future;
-use std::pin::Pin;
-
-use codex_protocol::ThreadId;
-
-/// Future returned by one host-owned internal-session spawning request.
-pub type InternalSessionSpawnFuture<'a, T, E> =
-    Pin<Box<dyn Future<Output = Result<T, E>> + Send + 'a>>;
-
-/// Constructor-injected host helper for extensions that need private internal sessions.
-///
-/// The extension owns the request shape and resulting handle types. The host
-/// provides the implementation when it constructs the extension.
-pub trait InternalSessionSpawner<R>: Send + Sync {
-    type Spawned;
-    type Error;
-
-    /// Starts a fresh host-owned internal session associated with its parent.
-    fn spawn_internal_session<'a>(
-        &'a self,
-        parent_thread_id: ThreadId,
-        request: R,
-    ) -> InternalSessionSpawnFuture<'a, Self::Spawned, Self::Error>;
-}
-
-impl<R, S, E, F> InternalSessionSpawner<R> for F
-where
-    F: Fn(ThreadId, R) -> InternalSessionSpawnFuture<'static, S, E> + Send + Sync,
-{
-    type Spawned = S;
-    type Error = E;
-
-    fn spawn_internal_session<'a>(
-        &'a self,
-        parent_thread_id: ThreadId,
-        request: R,
-    ) -> InternalSessionSpawnFuture<'a, Self::Spawned, Self::Error> {
-        self(parent_thread_id, request)
-    }
-}

codex-rs/ext/extension-api/src/capabilities/mod.rs

@@ -1,6 +1,5 @@
 mod conversation_history;
 mod events;
-mod internal_session;
 mod metrics;
 mod response_items;
 
@@ -8,8 +7,6 @@ pub use conversation_history::ConversationHistorySnapshot;
 pub use events::ExtensionEventSink;
 pub use events::ExtensionWarning;
 pub use events::NoopExtensionEventSink;
-pub use internal_session::InternalSessionSpawnFuture;
-pub use internal_session::InternalSessionSpawner;
 pub use metrics::ExtensionMetrics;
 pub use response_items::NoopResponseItemInjector;
 pub use response_items::ResponseItemInjectionFuture;

codex-rs/ext/extension-api/src/contributors.rs

@@ -24,8 +24,6 @@ mod world_state;
 
 pub use approval_review::ApprovalDecision;
 pub use approval_review::ApprovalDecisionInput;
-pub use approval_review::ApprovalReviewError;
-pub use approval_review::ApprovalReviewInput;
 pub use approval_review::GuardianV2Enabled;
 pub use approval_review::SynchronousApprovalReviewer;
 pub use context::TurnContextContributionInput;

codex-rs/ext/extension-api/src/contributors/approval_review.rs

@@ -1,58 +1,14 @@
 //! Request-scoped approval decisions. A review only satisfies the review gate; the host enforces permissions.
 
-use std::fmt;
 use std::sync::Arc;
 
 use codex_protocol::ThreadId;
-use serde_json::Value;
 
-use crate::ConversationHistorySnapshot;
 use crate::ExtensionData;
 
 /// Thread-local state installed only after Guardian V2's async classifier initializes.
 pub struct GuardianV2Enabled;
 
-/// Operational failure returned by an approval reviewer.
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub enum ApprovalReviewError {
-    /// The reviewer could not produce a valid assessment.
-    Failed(String),
-    /// The request exceeded its synchronous review deadline.
-    TimedOut,
-    /// The request was cancelled by its parent approval.
-    Cancelled,
-}
-
-impl fmt::Display for ApprovalReviewError {
-    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Failed(message) => write!(formatter, "approval review failed: {message}"),
-            Self::TimedOut => formatter.write_str("approval review timed out"),
-            Self::Cancelled => formatter.write_str("approval review was cancelled"),
-        }
-    }
-}
-
-impl std::error::Error for ApprovalReviewError {}
-
-/// Immutable context for reviewing an existing host-owned approval action.
-pub struct ApprovalReviewInput<'a> {
-    /// Structured action evidence rendered by the host's existing approval path.
-    pub action: &'a Value,
-    /// Canonical immutable conversation snapshot captured before review.
-    pub conversation_history: Arc<dyn ConversationHistorySnapshot>,
-    /// Stable host-owned thread identifier.
-    pub thread_id: ThreadId,
-    /// Store scoped to this thread runtime.
-    pub thread_store: &'a ExtensionData,
-    /// Stable host-owned turn identifier.
-    pub turn_id: &'a str,
-    /// Policy reason that caused the host to request approval.
-    pub approval_reason: Option<&'a str>,
-    /// Reason an earlier request is being retried, when applicable.
-    pub retry_reason: Option<&'a str>,
-}
-
 /// Guardian's choice for one approval. Synchronous results pass through unchanged.
 #[derive(Clone, Debug, PartialEq)]
 pub enum ApprovalDecision {

codex-rs/ext/extension-api/src/lib.rs

@@ -12,8 +12,6 @@ pub use capabilities::ConversationHistorySnapshot;
 pub use capabilities::ExtensionEventSink;
 pub use capabilities::ExtensionMetrics;
 pub use capabilities::ExtensionWarning;
-pub use capabilities::InternalSessionSpawnFuture;
-pub use capabilities::InternalSessionSpawner;
 pub use capabilities::NoopExtensionEventSink;
 pub use capabilities::NoopResponseItemInjector;
 pub use capabilities::ResponseItemInjectionFuture;
@@ -46,8 +44,6 @@ pub use codex_tools::parse_tool_input_schema_without_compaction;
 pub use contributors::ApprovalDecision;
 pub use contributors::ApprovalDecisionInput;
 pub use contributors::ApprovalReviewContributor;
-pub use contributors::ApprovalReviewError;
-pub use contributors::ApprovalReviewInput;
 pub use contributors::ConfigContributor;
 pub use contributors::ContextContributor;
 pub use contributors::ExtensionFuture;

codex-rs/ext/extension-api/tests/capabilities.rs

@@ -1,11 +1,5 @@
-use std::sync::Arc;
-use std::sync::Mutex;
-
-use codex_extension_api::InternalSessionSpawnFuture;
-use codex_extension_api::InternalSessionSpawner;
 use codex_extension_api::NoopResponseItemInjector;
 use codex_extension_api::ResponseItemInjector;
-use codex_protocol::ThreadId;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseInputItem;
 use pretty_assertions::assert_eq;
@@ -27,30 +21,3 @@ async fn noop_response_item_injector_returns_original_items() {
 
     assert_eq!(returned_items, items);
 }
-
-#[tokio::test]
-async fn closure_internal_session_spawner_forwards_arguments_and_result() {
-    let calls = Arc::new(Mutex::new(Vec::new()));
-    let recorded_calls = Arc::clone(&calls);
-    let spawner = move |thread_id: ThreadId,
-                        request: String|
-          -> InternalSessionSpawnFuture<'static, usize, &'static str> {
-        recorded_calls
-            .lock()
-            .expect("agent spawn calls lock")
-            .push((thread_id, request.clone()));
-        Box::pin(async move { Ok(request.len()) })
-    };
-    let thread_id =
-        ThreadId::from_string("11111111-1111-4111-8111-111111111111").expect("valid thread id");
-
-    let spawned = spawner
-        .spawn_internal_session(thread_id, "delegate this".to_string())
-        .await;
-
-    assert_eq!(spawned, Ok(13));
-    assert_eq!(
-        calls.lock().expect("agent spawn calls lock").as_slice(),
-        [(thread_id, "delegate this".to_string())]
-    );
-}

codex-rs/features/src/lib.rs

@@ -322,7 +322,7 @@ pub enum Feature {
     GuardianNodeReplTranscriptImages,
     /// Enable Guardian V2 automatic approval reviews.
     GuardianV2,
-    /// Enable the extension-owned synchronous Guardian reviewer.
+    /// Removed compatibility flag for the unused Guardian extension prototype.
     GuardianExt,
     /// Enable persisted thread goals and automatic goal continuation.
     Goals,
@@ -1610,7 +1610,7 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::GuardianExt,
         key: "guardian_ext",
-        stage: Stage::UnderDevelopment,
+        stage: Stage::Removed,
         default_enabled: false,
     },
     FeatureSpec {