test(hook): improve GenericRAGHook coverage for long_term_memory skip logic

Use scoreThreshold=0.0 to guarantee RAG retrieval triggers in the
hook-interference test, ensuring the name-based skip branch is
actually executed. Add edge-case test for when all USER messages
are hook-injected (no genuine user query available).

Author: hexly666

agentscope-extensions/agentscope-extensions-rag-simple/src/test/java/io/agentscope/core/rag/hook/GenericRAGHookTest.java

@@ -327,9 +327,22 @@ void testFormatKnowledgeContent() {
     @Test
     @DisplayName("Should skip long_term_memory injected messages when extracting query")
     void testSkipLongTermMemoryInjectedMessage() {
+        // Use scoreThreshold=0.0 to guarantee retrieval hits regardless of vector similarity
+        TestMockEmbeddingModel embeddingModel = new TestMockEmbeddingModel(DIMENSIONS);
+        InMemoryStore vectorStore = InMemoryStore.builder().dimensions(DIMENSIONS).build();
+        Knowledge zeroThresholdKnowledge =
+                SimpleKnowledge.builder()
+                        .embeddingModel(embeddingModel)
+                        .embeddingStore(vectorStore)
+                        .build();
+        RetrieveConfig zeroThresholdConfig =
+                RetrieveConfig.builder().limit(5).scoreThreshold(0.0).build();
+        GenericRAGHook hookWithZeroThreshold =
+                new GenericRAGHook(zeroThresholdKnowledge, zeroThresholdConfig);
+
         // Simulate StaticLongTermMemoryHook having already injected a "long_term_memory" message
         Document doc = createDocument("doc1", "Refund policy: 30 days return");
-        knowledge.addDocuments(List.of(doc)).block();
+        zeroThresholdKnowledge.addDocuments(List.of(doc)).block();
 
         List<Msg> inputMessages = new ArrayList<>();
         inputMessages.add(
@@ -349,20 +362,45 @@ void testSkipLongTermMemoryInjectedMessage() {
 
         PreCallEvent event = new PreCallEvent(mockAgent, inputMessages);
 
-        StepVerifier.create(hook.onEvent(event))
+        StepVerifier.create(hookWithZeroThreshold.onEvent(event))
                 .assertNext(
                         result -> {
                             List<Msg> messages = result.getInputMessages();
-                            // Should have original user msg + long_term_memory + RAG knowledge
+                            // Should have: original user msg + long_term_memory + RAG knowledge
                             assertEquals(3, messages.size());
-                            // The RAG hook should use the original user query, not the memory
-                            // message
+                            // The RAG hook must use the original user query, not the memory message
                             assertEquals("retrieved_knowledge", messages.get(2).getName());
                             assertTrue(messages.get(2).getTextContent().contains("knowledge base"));
                         })
                 .verifyComplete();
     }
 
+    @Test
+    @DisplayName("Should return no results when all user messages are hook-injected")
+    void testNoRealUserMessageWhenAllAreInjected() {
+        // Only hook-injected USER messages exist — no genuine user query
+        List<Msg> inputMessages = new ArrayList<>();
+        inputMessages.add(
+                Msg.builder()
+                        .role(MsgRole.USER)
+                        .name("long_term_memory")
+                        .content(
+                                TextBlock.builder()
+                                        .text("<long_term_memory>some memory</long_term_memory>")
+                                        .build())
+                        .build());
+
+        PreCallEvent event = new PreCallEvent(mockAgent, inputMessages);
+
+        StepVerifier.create(hook.onEvent(event))
+                .assertNext(
+                        result -> {
+                            // No real user query found: messages should remain unchanged
+                            assertEquals(1, result.getInputMessages().size());
+                        })
+                .verifyComplete();
+    }
+
     /**
      * Creates a test document.
      */