fix(client-java): keep Temurin 21 toolchain, auto-provision instead of bumping to 26

clients/java/build.gradle

@@ -18,7 +18,7 @@ subprojects {
     pluginManager.withPlugin('java') {
         java {
             toolchain {
-                languageVersion = JavaLanguageVersion.of(26)
+                languageVersion = JavaLanguageVersion.of(21)
             }
         }
 

clients/java/settings.gradle

@@ -9,6 +9,10 @@ pluginManagement {
     }
 }
 
+plugins {
+    id 'org.gradle.toolchains.foojay-resolver-convention' version '1.0.0'
+}
+
 dependencyResolutionManagement {
     repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
     repositories {

clients/java/zb-mom-ww-mxgateway-client/src/test/java/com/zb/mom/ww/mxgateway/client/GeneratedContractSmokeTests.java

@@ -1,7 +1,6 @@
 package com.zb.mom.ww.mxgateway.client;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import mxaccess_gateway.v1.MxAccessGatewayGrpc;
 import mxaccess_gateway.v1.MxaccessGateway.OpenSessionRequest;
@@ -25,8 +24,6 @@ final class GeneratedContractSmokeTests {
 
     @Test
     void javaTwentyOneToolchainRunsTests() {
-        // Accept Java 21 or later; locally macOS has JDK 26 (only JDK 26 is installed).
-        assertTrue(Runtime.version().feature() >= 21,
-                "expected Java 21+ but got " + Runtime.version());
+        assertEquals(21, Runtime.version().feature());
     }
 }