Always propagate checked exceptions from Kotlin code behind CGLIB proxies

Closes gh-23844

spring-aop/src/main/java/org/springframework/aop/framework/CglibAopProxy.java

@@ -48,6 +48,7 @@ import org.springframework.cglib.proxy.Factory;
 import org.springframework.cglib.proxy.MethodInterceptor;
 import org.springframework.cglib.proxy.MethodProxy;
 import org.springframework.cglib.proxy.NoOp;
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.SmartClassLoader;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -752,10 +753,17 @@ class CglibAopProxy implements AopProxy, Serializable {
 				throw ex;
 			}
 			catch (Exception ex) {
-				if (ReflectionUtils.declaresException(getMethod(), ex.getClass())) {
+				if (ReflectionUtils.declaresException(getMethod(), ex.getClass()) ||
+						KotlinDetector.isKotlinType(getMethod().getDeclaringClass())) {
+					// Propagate original exception if declared on the target method
+					// (with callers expecting it). Always propagate it for Kotlin code
+					// since checked exceptions do not have to be explicitly declared there.
 					throw ex;
 				}
 				else {
+					// Checked exception thrown in the interceptor but not declared on the
+					// target method signature -> apply an UndeclaredThrowableException,
+					// aligned with standard JDK dynamic proxy behavior.
 					throw new UndeclaredThrowableException(ex);
 				}
 			}