fix(security): [HIGH] resolve uncontrolled memory consumption DoS in automaton builder

src/main/java/org/eu/autogex/core/AbstractAutomatonBuilder.java

@@ -13,6 +13,9 @@
 public abstract class AbstractAutomatonBuilder<
         B extends AbstractAutomatonBuilder<B, A>, A extends Automaton> {
 
+    /** Maximum allowed states to prevent memory exhaustion (DoS) during manual construction. */
+    private static final int MAX_STATES = 10000;
+
     protected final Map<String, State> states = new HashMap<>();
     protected final Set<State> finalStates = new HashSet<>();
     protected State initialState;
@@ -39,6 +42,11 @@ protected AbstractAutomatonBuilder() {
      * @return The current builder instance.
      */
     public B addState(String name, boolean isFinal) {
+        if (states.size() >= MAX_STATES && !states.containsKey(name)) {
+            throw new IllegalStateException(
+                    "Builder state limit exceeded (Security: DoS prevention).");
+        }
+
         State state = new State(name, isFinal);
         states.put(name, state);
         if (isFinal) {

src/test/java/org/eu/autogex/core/AbstractAutomatonBuilderSecurityTest.java

@@ -0,0 +1,36 @@
+package org.eu.autogex.core;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class AbstractAutomatonBuilderSecurityTest {
+
+    static class TestBuilder extends AbstractAutomatonBuilder<TestBuilder, Automaton> {
+        @Override
+        protected TestBuilder self() {
+            return this;
+        }
+
+        @Override
+        public Automaton build() {
+            return null;
+        }
+    }
+
+    @Test
+    void testStateExplosionDoSPreventionInBuilder() {
+        TestBuilder builder = new TestBuilder();
+        for (int i = 0; i < 10000; i++) {
+            builder.addState("q" + i, false);
+        }
+
+        IllegalStateException exception =
+                assertThrows(
+                        IllegalStateException.class, () -> builder.addState("overflow", false));
+        assertTrue(
+                exception.getMessage().contains("Builder state limit exceeded"),
+                "Should detect state explosion to prevent DoS during manual construction");
+    }
+}