diff --git a/argi-graph-core/src/main/java/io/github/agentic/ai/graph/OverAllState.java b/argi-graph-core/src/main/java/io/github/agentic/ai/graph/OverAllState.java
index 388541848..a56f47986 100644
--- a/argi-graph-core/src/main/java/io/github/agentic/ai/graph/OverAllState.java
+++ b/argi-graph-core/src/main/java/io/github/agentic/ai/graph/OverAllState.java
@@ -169,8 +169,13 @@ public OverAllState(Store store) {
 	 */
 	protected OverAllState(Map<String, Object> data, Map<String, KeyStrategy> keyStrategies) {
 		this.data = data != null ? new HashMap<>(data) : new HashMap<>();
-		this.keyStrategies = keyStrategies != null ? keyStrategies : new HashMap<>();
-		this.registerKeyAndStrategy(OverAllState.DEFAULT_INPUT_KEY, new ReplaceStrategy());
+		// defensive copy: the default-input registration below must not leak into a map
+		// the caller still owns (e.g. the CompiledGraph's shared keyStrategyMap, which
+		// cloneState hands over by reference and every checkpoint would otherwise mutate)
+		this.keyStrategies = keyStrategies != null ? new HashMap<>(keyStrategies) : new HashMap<>();
+		// register the default input strategy only when the caller did not provide one,
+		// so user-registered strategies (e.g. AppendStrategy) survive cloning/snapshots
+		this.keyStrategies.putIfAbsent(OverAllState.DEFAULT_INPUT_KEY, new ReplaceStrategy());
 	}
 
 	/**
@@ -182,8 +187,9 @@ protected OverAllState(Map<String, Object> data, Map<String, KeyStrategy> keyStr
 	protected OverAllState(Map<String, Object> data, Map<String, KeyStrategy> keyStrategies,
 			Store store) {
 		this.data = data != null ? new HashMap<>(data) : new HashMap<>();
-		this.keyStrategies = keyStrategies != null ? keyStrategies : new HashMap<>();
-		this.registerKeyAndStrategy(OverAllState.DEFAULT_INPUT_KEY, new ReplaceStrategy());
+		// defensive copy, same rationale as the two-argument constructor
+		this.keyStrategies = keyStrategies != null ? new HashMap<>(keyStrategies) : new HashMap<>();
+		this.keyStrategies.putIfAbsent(OverAllState.DEFAULT_INPUT_KEY, new ReplaceStrategy());
 		this.store = store;
 	}
 
diff --git a/argi-graph-core/src/test/java/io/github/agentic/ai/graph/CloneStateKeyStrategyPollutionTest.java b/argi-graph-core/src/test/java/io/github/agentic/ai/graph/CloneStateKeyStrategyPollutionTest.java
new file mode 100644
index 000000000..46f0e8640
--- /dev/null
+++ b/argi-graph-core/src/test/java/io/github/agentic/ai/graph/CloneStateKeyStrategyPollutionTest.java
@@ -0,0 +1,92 @@
+package io.github.agentic.ai.graph;
+
+import io.github.agentic.ai.graph.action.NodeAction;
+import io.github.agentic.ai.graph.state.strategy.AppendStrategy;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static io.github.agentic.ai.graph.StateGraph.END;
+import static io.github.agentic.ai.graph.StateGraph.START;
+import static io.github.agentic.ai.graph.action.AsyncNodeAction.node_async;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+
+/**
+ * Reproduction for the keyStrategy aliasing/overwrite issue reported upstream in
+ * alibaba/spring-ai-alibaba#4999 (same code inherited by argi-graph-core):
+ *
+ * 1. CompiledGraph.cloneState passes the compiled graph's shared keyStrategyMap
+ *    into the 2-arg OverAllState constructor by reference, whose unconditional
+ *    registerKeyAndStrategy(DEFAULT_INPUT_KEY, new ReplaceStrategy()) then
+ *    mutates the shared map on the first checkpoint (GraphRunnerContext.addCheckpoint).
+ * 2. Even with a defensive copy, the unconditional default-input registration
+ *    still silently replaces a user-registered "input" strategy on every clone
+ *    and snapshot (OverAllState.snapShot, used by ParallelNode/ConditionalParallelNode),
+ *    so Append/Merge semantics degrade to REPLACE exactly where cloning is involved.
+ */
+public class CloneStateKeyStrategyPollutionTest {
+
+	@Test
+	public void cloneStateMustNotMutateCompiledGraphKeyStrategyMap() throws Exception {
+		KeyStrategyFactory keyStrategyFactory = () -> {
+			Map<String, KeyStrategy> m = new HashMap<>();
+			m.put("input", new AppendStrategy());
+			m.put("messages", new AppendStrategy());
+			return m;
+		};
+
+		NodeAction agent = state -> Map.of("messages", "hello");
+
+		var workflow = new StateGraph(keyStrategyFactory)
+			.addNode("agent", node_async(agent))
+			.addEdge(START, "agent")
+			.addEdge("agent", END);
+
+		// compile() registers a MemorySaver by default, so every node output
+		// triggers addCheckpoint -> cloneState
+		var app = workflow.compile();
+
+		// right after compile, the user-registered strategy is intact
+		assertInstanceOf(AppendStrategy.class, app.getKeyStrategyMap().get("input"));
+
+		app.invoke(Map.of("input", "a"));
+
+		// after the first checkpoint, the shared keyStrategyMap must still hold
+		// the user-registered strategy for "input"
+		assertInstanceOf(AppendStrategy.class, app.getKeyStrategyMap().get("input"),
+				"cloneState must not pollute the CompiledGraph's shared keyStrategyMap");
+	}
+
+	@Test
+	public void cloneStateAndSnapShotMustPreserveUserRegisteredInputStrategy() throws Exception {
+		KeyStrategyFactory keyStrategyFactory = () -> {
+			Map<String, KeyStrategy> m = new HashMap<>();
+			m.put("input", new AppendStrategy());
+			m.put("messages", new AppendStrategy());
+			return m;
+		};
+
+		NodeAction agent = state -> Map.of("messages", "hello");
+
+		var app = new StateGraph(keyStrategyFactory)
+			.addNode("agent", node_async(agent))
+			.addEdge(START, "agent")
+			.addEdge("agent", END)
+			.compile();
+
+		var clone = app.cloneState(Map.of("input", "a"));
+
+		// the clone handed to checkpoints / interrupt hooks must keep the
+		// user-registered merge semantics for "input"
+		assertInstanceOf(AppendStrategy.class, clone.keyStrategies().get("input"),
+				"cloneState must preserve the user-registered 'input' KeyStrategy");
+
+		var snapShot = clone.snapShot().orElseThrow();
+
+		// same for snapshots taken from the clone (ParallelNode/ConditionalParallelNode path)
+		assertInstanceOf(AppendStrategy.class, snapShot.keyStrategies().get("input"),
+				"snapShot must preserve the user-registered 'input' KeyStrategy");
+	}
+
+}