Fix POSIXisms: use TestUtil.tempPath() for cross-platform temp paths

Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/b7de171b-6625-4ab4-b222-4858b0cacfc2

Co-authored-by: edburns <75821+edburns@users.noreply.github.com>

Author: Copilot

src/test/java/com/github/copilot/sdk/TestUtil.java

@@ -10,13 +10,27 @@
 import java.nio.file.Paths;
 
 /**
- * Shared test utilities for locating the Copilot CLI binary.
+ * Shared test utilities for locating the Copilot CLI binary and other
+ * cross-platform test helpers.
  */
-final class TestUtil {
+public final class TestUtil {
 
     private TestUtil() {
     }
 
+    /**
+     * Returns a platform-independent path string for a file inside the system
+     * temporary directory. Uses {@code java.io.tmpdir} so tests run correctly on
+     * both POSIX and Windows.
+     *
+     * @param filename
+     *            the file name (no directory separator required)
+     * @return absolute path string in the system temp directory
+     */
+    public static String tempPath(String filename) {
+        return Path.of(System.getProperty("java.io.tmpdir"), filename).toString();
+    }
+
     /**
      * Locates a launchable Copilot CLI executable.
      * <p>

src/test/java/com/github/copilot/sdk/generated/rpc/GeneratedRpcRecordsCoverageTest.java

@@ -12,6 +12,8 @@
 
 import org.junit.jupiter.api.Test;
 
+import com.github.copilot.sdk.TestUtil;
+
 /**
  * Tests for generated RPC param and result record types. Exercises
  * constructors, field accessors, and enum variants to provide JaCoCo coverage
@@ -144,25 +146,25 @@ void sessionFleetStartParams_record() {
 
     @Test
     void sessionFsAppendFileParams_record() {
-        var params = new SessionFsAppendFileParams("sess-12", "/tmp/log.txt", "new line\n", null);
+        var params = new SessionFsAppendFileParams("sess-12", TestUtil.tempPath("log.txt"), "new line\n", null);
         assertEquals("sess-12", params.sessionId());
-        assertEquals("/tmp/log.txt", params.path());
+        assertEquals(TestUtil.tempPath("log.txt"), params.path());
         assertEquals("new line\n", params.content());
         assertNull(params.mode());
     }
 
     @Test
     void sessionFsExistsParams_record() {
-        var params = new SessionFsExistsParams("sess-13", "/tmp/file.txt");
+        var params = new SessionFsExistsParams("sess-13", TestUtil.tempPath("file.txt"));
         assertEquals("sess-13", params.sessionId());
-        assertEquals("/tmp/file.txt", params.path());
+        assertEquals(TestUtil.tempPath("file.txt"), params.path());
     }
 
     @Test
     void sessionFsMkdirParams_record() {
-        var params = new SessionFsMkdirParams("sess-14", "/tmp/newdir", true, null);
+        var params = new SessionFsMkdirParams("sess-14", TestUtil.tempPath("newdir"), true, null);
         assertEquals("sess-14", params.sessionId());
-        assertEquals("/tmp/newdir", params.path());
+        assertEquals(TestUtil.tempPath("newdir"), params.path());
         assertTrue(params.recursive());
         assertNull(params.mode());
     }
@@ -198,9 +200,9 @@ void sessionFsRenameParams_record() {
 
     @Test
     void sessionFsRmParams_record() {
-        var params = new SessionFsRmParams("sess-19", "/tmp/file.txt", false, true);
+        var params = new SessionFsRmParams("sess-19", TestUtil.tempPath("file.txt"), false, true);
         assertEquals("sess-19", params.sessionId());
-        assertEquals("/tmp/file.txt", params.path());
+        assertEquals(TestUtil.tempPath("file.txt"), params.path());
         assertFalse(params.recursive());
         assertTrue(params.force());
     }
@@ -224,11 +226,11 @@ void sessionFsStatParams_record() {
 
     @Test
     void sessionFsWriteFileParams_record() {
-        var params = new SessionFsWriteFileParams("sess-21", "/tmp/out.txt", "content here", 644.0);
+        var params = new SessionFsWriteFileParams("sess-21", TestUtil.tempPath("out.txt"), "content here", null);
         assertEquals("sess-21", params.sessionId());
-        assertEquals("/tmp/out.txt", params.path());
+        assertEquals(TestUtil.tempPath("out.txt"), params.path());
         assertEquals("content here", params.content());
-        assertEquals(644.0, params.mode());
+        assertNull(params.mode());
     }
 
     @Test