[router] router circuit breaker core (#8941)

sgl-router/src/core/mod.rs

@@ -3,12 +3,17 @@
 //! This module contains the fundamental types and traits used throughout the router:
 //! - Worker trait and implementations
 //! - Error types
+//! - Circuit breaker for reliability
 //! - Common utilities
 
+pub mod circuit_breaker;
 pub mod error;
 pub mod worker;
 
 // Re-export commonly used types at the module level
+pub use circuit_breaker::{
+    CircuitBreaker, CircuitBreakerConfig, CircuitBreakerStats, CircuitState,
+};
 pub use error::{WorkerError, WorkerResult};
 pub use worker::{
     start_health_checker, BasicWorker, DPAwareWorker, HealthChecker, Worker, WorkerCollection,