Add vLLM v0.18.1 source tree with KV transfer abort fix

third_party/vllm/ now tracked in git for direct patch management.
Based on vLLM v0.18.1 release with one patch applied:

  vllm/v1/core/sched/scheduler.py:
    Replace fatal assert with graceful skip when KV transfer callback
    arrives for an already-aborted request during PD disaggregated serving.

Future vLLM modifications should be made directly in third_party/vllm/
and committed normally. The patches/ directory is kept as documentation
of what changed from upstream.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

third_party/vllm/tests/evals/gsm8k/conftest.py

@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from pathlib import Path
+
+
+def pytest_addoption(parser):
+    """Add custom command line options."""
+    parser.addoption(
+        "--config-list-file",
+        default="configs/models-small.txt",
+        help="File containing list of config files to test",
+    )
+
+
+def pytest_generate_tests(metafunc):
+    """Generate test parameters from config files."""
+    if "config_filename" in metafunc.fixturenames:
+        config_list_file = metafunc.config.getoption("--config-list-file")
+
+        # Handle both relative and absolute paths
+        config_list_path = Path(config_list_file)
+        if not config_list_path.is_absolute():
+            # If relative, try relative to test directory first
+            test_dir_path = Path(__file__).parent / config_list_file
+            if test_dir_path.exists():
+                config_list_path = test_dir_path
+            else:
+                # Try relative to current working directory
+                config_list_path = Path.cwd() / config_list_file
+
+        print(f"Looking for config list at: {config_list_path}")
+
+        config_files = []
+        if config_list_path.exists():
+            # Determine config directory (same directory as the list file)
+            config_dir = config_list_path.parent
+
+            with open(config_list_path) as f:
+                for line in f:
+                    line = line.strip()
+                    if line and not line.startswith("#"):
+                        config_path = config_dir / line
+                        print(f"Checking config file: {config_path}")
+                        if config_path.exists():
+                            config_files.append(config_path)
+                            print(f"  ✓ Found: {config_path}")
+                        else:
+                            print(f"  ✗ Missing: {config_path}")
+        else:
+            print(f"Config list file not found: {config_list_path}")
+
+        # Generate test parameters
+        if config_files:
+            metafunc.parametrize(
+                "config_filename",
+                config_files,
+                ids=[config_file.stem for config_file in config_files],
+            )
+        else:
+            print("No config files found, test will be skipped")