fix(exec): 同步 UTF-8 输出解码修复（JDK 17 线直接可用 toString(Charset)）

Author: loong10k

src/main/java/io/github/easy4j/opencode/cli/OpenCodeCliExecutor.java

@@ -11,6 +11,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.util.Objects;
 
 /**
@@ -77,8 +78,10 @@ public OpenCodeCliResult execute(String... args) {
 
         try {
             int exitCode = executor.execute(cmd);
-            String out = stdout.toString().trim();
-            String err = stderr.toString().trim();
+            // 显式 UTF-8 解码：toString() 走平台默认字符集，GBK 默认字符集的
+            // Windows 上会把 opencode 的 UTF-8 输出解成乱码。
+            String out = stdout.toString(StandardCharsets.UTF_8).trim();
+            String err = stderr.toString(StandardCharsets.UTF_8).trim();
             if (config.getDebug().allows(HttpLogLevel.BASIC)) {
                 log.debug("OpenCode CLI executed: exitCode={}, stdoutLength={}, stderrLength={}",
                         exitCode, out.length(), err.length());

src/test/java/io/github/easy4j/opencode/cli/OpenCodeCliExecutorTest.java

@@ -15,6 +15,22 @@ void shouldRejectNullConfig() {
         assertThrows(NullPointerException.class, () -> new OpenCodeCliExecutor(null));
     }
 
+    @Test
+    void shouldDecodeUtf8OutputFromChildProcess() {
+        // 子进程经 POSIX printf 八进制转义输出"你好"的 UTF-8 字节
+        //（\344\275\240\345\245\275）。源码必须写双反斜杠：Java 字面量里
+        // 的 \344 会被编译器当八进制转义吃掉。
+        OpenCodeCliConfig config = new OpenCodeCliConfig();
+        config.setExecutable("sh");
+        config.setTimeout(5);
+        OpenCodeCliExecutor executor = new OpenCodeCliExecutor(config);
+
+        OpenCodeCliResult result = executor.execute("-c", "printf '\\344\\275\\240\\345\\245\\275'");
+
+        assertTrue(result.isSuccess());
+        assertEquals("你好", result.getStdout(), "UTF-8 输出必须按 UTF-8 解码，而非平台默认字符集");
+    }
+
     @Test
     void shouldExecuteSimpleCommand() {
         OpenCodeCliConfig config = new OpenCodeCliConfig();