fix: reject JDK < 11 early with clear error message

When running with JDK 8, the pipeline would fail late with a cryptic
UnsupportedClassVersionError from the runtime JAR. Now checks the
detected Java version in ensure_runtime_environment() and returns False
with a clear error message explaining that JDK 11+ is required.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mohamedashrraf222

codeflash/languages/java/support.py

@@ -546,6 +546,21 @@ def ensure_runtime_environment(self, project_root: Path) -> bool:
         if self._language_version is None:
             self._detect_java_version()
 
+        if self._language_version is not None:
+            try:
+                major = int(self._language_version)
+                if major < 11:
+                    logger.error(
+                        "Java %s detected, but codeflash requires JDK 11 or later. "
+                        "The codeflash-runtime JAR and --add-opens flags are incompatible with JDK %s. "
+                        "Please install JDK 11+ and ensure it is on your PATH.",
+                        self._language_version,
+                        self._language_version,
+                    )
+                    return False
+            except ValueError:
+                pass
+
         self._test_framework = config.test_framework
 
         return True

tests/test_languages/test_java/test_support.py

@@ -134,3 +134,44 @@ def test_discover_functions_from_fixture(self, support, java_fixture_path: Path)
         source = calculator_file.read_text(encoding="utf-8")
         functions = support.discover_functions(source, calculator_file)
         assert len(functions) > 0
+
+
+class TestJdkVersionCheck:
+    def test_jdk8_rejected(self, tmp_path: Path) -> None:
+        from unittest.mock import MagicMock, patch
+
+        support = get_java_support()
+
+        mock_config = MagicMock()
+        mock_config.java_version = "8"
+        mock_config.test_framework = "junit5"
+
+        with patch("codeflash.languages.java.support.detect_java_project", return_value=mock_config):
+            result = support.ensure_runtime_environment(tmp_path)
+        assert result is False
+
+    def test_jdk11_accepted(self, tmp_path: Path) -> None:
+        from unittest.mock import MagicMock, patch
+
+        support = get_java_support()
+
+        mock_config = MagicMock()
+        mock_config.java_version = "11"
+        mock_config.test_framework = "junit5"
+
+        with patch("codeflash.languages.java.support.detect_java_project", return_value=mock_config):
+            result = support.ensure_runtime_environment(tmp_path)
+        assert result is True
+
+    def test_jdk21_accepted(self, tmp_path: Path) -> None:
+        from unittest.mock import MagicMock, patch
+
+        support = get_java_support()
+
+        mock_config = MagicMock()
+        mock_config.java_version = "21"
+        mock_config.test_framework = "junit5"
+
+        with patch("codeflash.languages.java.support.detect_java_project", return_value=mock_config):
+            result = support.ensure_runtime_environment(tmp_path)
+        assert result is True