fix: LlmAgent model name resolution and improve Gemini-3 model detection logic

core/src/main/java/com/google/adk/agents/LlmAgent.java

@@ -965,7 +965,10 @@ private Model resolveModelInternal() {
       Model currentModel = this.model.get();
 
       if (currentModel.model().isPresent()) {
-        return currentModel;
+        String modelName = currentModel.model().get().model();
+        BaseLlm resolvedLlm = currentModel.model().get();
+
+        return Model.builder().modelName(modelName).model(resolvedLlm).build();
       }
 
       if (currentModel.modelName().isPresent()) {

core/src/main/java/com/google/adk/flows/llmflows/Contents.java

@@ -559,7 +559,7 @@ private static List<Event> rearrangeEventsForAsyncFunctionResponsesInHistory(
 
     // Gemini 3 requires function calls to be grouped first and only then function responses:
     // FC1 FC2 FR1 FR2
-    boolean shouldBufferResponseEvents = modelName.startsWith("gemini-3-");
+    boolean shouldBufferResponseEvents = modelName.contains("gemini-3-");
 
     for (int i = 0; i < events.size(); i++) {
       Event event = events.get(i);

core/src/test/java/com/google/adk/agents/LlmAgentTest.java

@@ -376,6 +376,17 @@ public void resolveModel_withModelName_resolvesFromRegistry() {
     assertThat(resolvedModel.model()).hasValue(testLlm);
   }
 
+  @Test
+  public void resolveModel_withModel_usesProvidedModel() {
+    TestLlm testLlm = createTestLlm(LlmResponse.builder().build());
+    LlmAgent testAgent = createTestAgent(testLlm);
+
+    Model resolvedModel = testAgent.resolvedModel();
+
+    assertThat(resolvedModel.model()).hasValue(testLlm);
+    assertThat(resolvedModel.modelName()).hasValue(testLlm.model());
+  }
+
   @Test
   public void canonicalCallbacks_returnsEmptyListWhenNull() {
     TestLlm testLlm = createTestLlm(LlmResponse.builder().build());