fix: lazily initialize tokenizer HTTP client

src/main/java/com/google/genai/LocalTokenizerLoader.java

@@ -129,10 +129,21 @@ public String toString() {
   private static final Map<String, ModelProto> modelProtoCache = new ConcurrentHashMap<>();
   private static final Map<String, LocalTokenizerProcessor> localTokenizerProcessorCache =
       new ConcurrentHashMap<>();
-  private static OkHttpClient httpClient = new OkHttpClient();
+  // Non-null only when replaced by tests.
+  private static OkHttpClient httpClient;
 
   private LocalTokenizerLoader() {}
 
+  private static final class HttpClientHolder {
+    private static final OkHttpClient INSTANCE = new OkHttpClient();
+
+    private HttpClientHolder() {}
+  }
+
+  private static OkHttpClient getHttpClient() {
+    return httpClient != null ? httpClient : HttpClientHolder.INSTANCE;
+  }
+
   /** Gets the tokenizer name for the given model name. */
   public static String getTokenizerName(String modelName) {
     if (GEMINI_MODELS_TO_TOKENIZER_NAMES.containsKey(modelName)) {
@@ -240,7 +251,7 @@ private static void maybeSaveToCache(Path cacheDir, Path cachePath, byte[] conte
 
   private static byte[] loadFromUrl(String fileUrl, String expectedHash) throws IOException {
     Request request = new Request.Builder().url(fileUrl).build();
-    try (Response response = httpClient.newCall(request).execute()) {
+    try (Response response = getHttpClient().newCall(request).execute()) {
       if (response == null) {
         throw new GenAiIOException("HTTP request failed: response is null");
       }

src/test/java/com/google/genai/LocalTokenizerLoaderTest.java

@@ -19,6 +19,7 @@
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -98,11 +99,22 @@ void setUp() throws Exception {
   @AfterEach
   void tearDown() throws Exception {
     System.setProperty("java.io.tmpdir", originalTmpDir);
+    Field clientField = LocalTokenizerLoader.class.getDeclaredField("httpClient");
+    setStatic(clientField, null);
     // Restore original tokenizers map
     Field tokenizersField = LocalTokenizerLoader.class.getDeclaredField("TOKENIZERS");
     setStatic(tokenizersField, originalTokenizers);
   }
 
+  @Test
+  void getTokenizerName_doesNotInitializeHttpClient() throws Exception {
+    Field clientField = LocalTokenizerLoader.class.getDeclaredField("httpClient");
+    setStatic(clientField, null);
+
+    assertEquals("gemma3", LocalTokenizerLoader.getTokenizerName("gemini-2.5-pro"));
+    assertNull(clientField.get(null));
+  }
+
   @Test
   void getTokenizerName_supportedModels() {
     assertEquals("gemma3", LocalTokenizerLoader.getTokenizerName("gemini-2.5-pro"));