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/tools/test_config_validator.py

@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import ast
+
+import pytest
+
+from tools.pre_commit.validate_config import validate_ast
+
+_TestConfig1 = '''
+@config
+class _TestConfig1:
+    a: int
+    """docstring"""
+'''
+
+_TestConfig2 = """
+@config
+class _TestConfig2:
+    a: int = 1
+"""
+
+_TestConfig3 = '''
+@config
+class _TestConfig3:
+    a: Union[Literal[1], Literal[2]] = 1
+    """docstring"""
+'''
+
+
+@pytest.mark.parametrize(
+    ("test_config", "expected_error"),
+    [
+        (_TestConfig1, "must have a default"),
+        (_TestConfig2, "must have a docstring"),
+        (_TestConfig3, "must use a single Literal"),
+    ],
+)
+def test_config(test_config, expected_error):
+    tree = ast.parse(test_config)
+    with pytest.raises(Exception, match=expected_error):
+        validate_ast(tree)