Propagate MCP elicitation event delivery failures (#38035)

## Why

When the event receiver is closed, an MCP elicitation request cannot reach its
consumer. Ignoring that delivery failure leaves the request and its lifecycle
registration pending while waiting for a response that cannot arrive.

## What changed

Return a contextual error when an MCP elicitation event cannot be delivered.
This drops the pending-request guard immediately, removing the responder from
the router and releasing its lifecycle registration.

## Testing

Add a regression test that closes the event channel and verifies the request
fails immediately, the router is empty, and the lifecycle registration is
released.

GitOrigin-RevId: 1067f35a5775d61c5bcd07b4b190d3907d8f219a

codex-rs/codex-mcp/src/elicitation.rs

@@ -418,7 +418,7 @@ impl ElicitationRequestManager {
                     router: router.clone(),
                     key: request_key,
                 };
-                let _ = tx_event
+                tx_event
                     .send(Event {
                         id: "mcp_elicitation_request".to_string(),
                         msg: EventMsg::ElicitationRequest(ElicitationRequestEvent {
@@ -428,7 +428,8 @@ impl ElicitationRequestManager {
                             request,
                         }),
                     })
-                    .await;
+                    .await
+                    .context("failed to deliver MCP elicitation request")?;
                 rx.await
                     .context("elicitation request channel closed unexpectedly")
             }

codex-rs/codex-mcp/src/elicitation_tests.rs

@@ -118,6 +118,52 @@ async fn assert_declined(marker: Value, response: Option<ReviewerResponse>) {
     assert!(events.is_empty());
 }
 
+#[test]
+fn closed_event_channel_immediately_cleans_up_pending_elicitation() {
+    let active_elicitations = Arc::new(AtomicUsize::new(0));
+    let registrations = active_elicitations.clone();
+    let lifecycle = ElicitationLifecycle::new(move || {
+        registrations.fetch_add(/*val*/ 1, Relaxed);
+        LifecycleRegistration(registrations.clone())
+    });
+    let (manager, events, sender) = elicitation_fixture(
+        AskForApproval::OnRequest,
+        PermissionProfile::Disabled,
+        /*reviewer*/ None,
+    );
+    assert!(manager.update(
+        AskForApproval::OnRequest,
+        PermissionProfile::Disabled,
+        /*reviewer*/ None,
+        Some(lifecycle),
+    ));
+    drop(events);
+
+    let elicitation = Elicitation::Mcp(ElicitRequestParams::FormElicitationParams {
+        meta: None,
+        message: "Review this request".to_string(),
+        requested_schema: ElicitationSchema::builder().build().unwrap(),
+    });
+    let error = sender(RequestId::Number(7), elicitation)
+        .now_or_never()
+        .expect("closed event channel must not leave an elicitation pending")
+        .expect_err("closed event channel must fail the elicitation");
+
+    assert_eq!(
+        error.to_string(),
+        "failed to deliver MCP elicitation request"
+    );
+    assert!(
+        manager
+            .router
+            .requests
+            .lock()
+            .expect("pending request router should be available")
+            .is_empty()
+    );
+    assert_eq!(active_elicitations.load(Relaxed), 0);
+}
+
 #[tokio::test]
 async fn strict_auto_review_respects_explicit_elicitation_denials() {
     for policy in [