Fix invalid prototype slot node issue

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slotchain/DefaultProcessorSlotChain.java

@@ -16,6 +16,7 @@
 package com.alibaba.csp.sentinel.slotchain;
 
 import com.alibaba.csp.sentinel.context.Context;
+import com.alibaba.csp.sentinel.slots.block.flow.PrototypeSlotWrapper;
 
 /**
  * @author qinan.qn
@@ -50,8 +51,9 @@ public void addFirst(AbstractLinkedProcessorSlot<?> protocolProcessor) {
 
     @Override
     public void addLast(AbstractLinkedProcessorSlot<?> protocolProcessor) {
-        end.setNext(protocolProcessor);
-        end = protocolProcessor;
+        PrototypeSlotWrapper processor = new PrototypeSlotWrapper(protocolProcessor);
+        end.setNext(processor);
+        end = processor;
     }
 
     /**

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/PrototypeSlotWrapper.java

@@ -0,0 +1,39 @@
+package com.alibaba.csp.sentinel.slots.block.flow;
+
+import com.alibaba.csp.sentinel.context.Context;
+import com.alibaba.csp.sentinel.slotchain.AbstractLinkedProcessorSlot;
+import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
+
+/**
+ * @author joyce
+ * @date 2026/5/14
+ * @since 1.8.5
+ **/
+public class PrototypeSlotWrapper extends AbstractLinkedProcessorSlot<Object> {
+
+    private final AbstractLinkedProcessorSlot delegate;
+
+    public PrototypeSlotWrapper(AbstractLinkedProcessorSlot delegate) {
+        this.delegate = delegate;
+    }
+
+    @Override
+    public void fireEntry(Context context, ResourceWrapper resourceWrapper, Object obj, int count, boolean prioritized, Object... args) throws Throwable {
+        this.delegate.fireEntry(context, resourceWrapper, obj, count, prioritized, args);
+    }
+
+    @Override
+    public void fireExit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
+        this.delegate.fireExit(context, resourceWrapper, count, args);
+    }
+
+    @Override
+    public void entry(Context context, ResourceWrapper resourceWrapper, Object param, int count, boolean prioritized, Object... args) throws Throwable {
+        delegate.entry(context, resourceWrapper, param, count, prioritized, args);
+    }
+
+    @Override
+    public void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
+        delegate.exit(context, resourceWrapper, count, args);
+    }
+}

sentinel-core/src/test/java/com/alibaba/csp/sentinel/slots/ProcessorSlotChainTest.java

@@ -0,0 +1,76 @@
+package com.alibaba.csp.sentinel.slots;
+
+import com.alibaba.csp.sentinel.context.Context;
+import com.alibaba.csp.sentinel.slotchain.AbstractLinkedProcessorSlot;
+import com.alibaba.csp.sentinel.slotchain.DefaultProcessorSlotChain;
+import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
+import org.junit.Assert;
+import org.junit.Test;
+import org.mockito.Mockito;
+import java.lang.reflect.Field;
+
+/**
+ * @author joyce
+ * @date 2026/5/14
+ */
+public class ProcessorSlotChainTest {
+
+    @Test
+    public void testBeforeFix_nextOfSingletonIsShared() throws Exception {
+        DefaultSlot singleton = new DefaultSlot();
+        DefaultProcessorSlotChain chain1 = createLegacyChain();
+        DefaultProcessorSlotChain chain2 = createLegacyChain();
+
+        DefaultSlot prototypeA1 = new DefaultSlot();
+        chain1.addLast(singleton);
+        chain1.addLast(prototypeA1);
+
+        DefaultSlot prototypeA2 = new DefaultSlot();
+        chain2.addLast(singleton);
+        chain2.addLast(prototypeA2);
+
+        Assert.assertEquals(chain1.getNext().getNext(), chain2.getNext().getNext());
+    }
+    @Test
+    public void testAfterFix_eachChainHasItsOwnWrapper() {
+        DefaultSlot singleton = new DefaultSlot();
+        DefaultProcessorSlotChain chain1 = new DefaultProcessorSlotChain();
+        DefaultProcessorSlotChain chain2 = new DefaultProcessorSlotChain();
+
+        chain1.addLast(singleton);
+        chain1.addLast(new DefaultSlot());
+
+        chain2.addLast(singleton);
+        chain2.addLast(new DefaultSlot());
+        Assert.assertNotEquals(chain1.getNext().getNext(), chain2.getNext().getNext());
+    }
+
+    private DefaultProcessorSlotChain createLegacyChain() throws Exception {
+        DefaultProcessorSlotChain chain = Mockito.spy(new DefaultProcessorSlotChain());
+        Field endField = DefaultProcessorSlotChain.class.getDeclaredField("end");
+        endField.setAccessible(true);
+
+        Mockito.doAnswer(invocation -> {
+            AbstractLinkedProcessorSlot<?> slot = invocation.getArgument(0);
+            AbstractLinkedProcessorSlot<?> end =
+                    (AbstractLinkedProcessorSlot<?>) endField.get(chain);
+            end.setNext(slot);
+            endField.set(chain, slot);
+            return null;
+        }).when(chain).addLast(Mockito.any(AbstractLinkedProcessorSlot.class));
+
+        return chain;
+    }
+
+    private static class DefaultSlot extends AbstractLinkedProcessorSlot<Object> {
+
+        @Override
+        public void entry(Context context, ResourceWrapper resourceWrapper, Object t, int count,
+                          boolean prioritized, Object... args) throws Throwable {
+        }
+
+        @Override
+        public void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
+        }
+    }
+}