refactor: make StateSnapshot inherit from NodeOutput

work on #24

core-jdk8/src/main/java/org/bsc/langgraph4j/state/StateSnapshot.java

@@ -1,32 +1,49 @@
 package org.bsc.langgraph4j.state;
 
 import lombok.NonNull;
-import lombok.Value;
-import lombok.var;
+import org.bsc.langgraph4j.NodeOutput;
 import org.bsc.langgraph4j.RunnableConfig;
 import org.bsc.langgraph4j.checkpoint.Checkpoint;
 
-@Value
-public class StateSnapshot<State extends AgentState> {
-    State state;
-    RunnableConfig config;
+public final class StateSnapshot<State extends AgentState> extends NodeOutput<State> {
+    private final RunnableConfig config;
 
-    public String getNext( ) {
+    public String next( ) {
         return config.nextNode().orElse(null);
     }
 
-    private StateSnapshot(@NonNull State state, @NonNull RunnableConfig config) {
-        this.state = state;
+    public RunnableConfig config() {
+        return config;
+    }
+
+    /**
+     * @deprecated Use {@link #config()} instead.
+     */
+    @Deprecated
+    public RunnableConfig getConfig( ) {
+        return config();
+    }
+
+    /**
+     * @deprecated Use {@link #next()} instead.
+     */
+    @Deprecated
+    public String getNext( ) {
+        return next();
+    }
+
+    private StateSnapshot(@NonNull String node, @NonNull State state, @NonNull RunnableConfig config) {
+        super( node, state );
         this.config = config;
     }
 
     public static <State extends AgentState> StateSnapshot<State> of(Checkpoint checkpoint, RunnableConfig config, AgentStateFactory<State> factory) {
 
-        var newConfig = RunnableConfig.builder(config)
+        RunnableConfig newConfig = RunnableConfig.builder(config)
                                 .checkPointId( checkpoint.getId() )
                                 .nextNode( checkpoint.getNextNodeId() )
                                 .build() ;
-        return new StateSnapshot<>( factory.apply(checkpoint.getState()), newConfig);
+        return new StateSnapshot<>( checkpoint.getNodeId(), factory.apply(checkpoint.getState()), newConfig);
     }
 
 }