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/examples/offline_inference/save_sharded_state.py

@@ -0,0 +1,85 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Saves each worker's model state dict directly to a checkpoint, which enables a
+fast load path for large tensor-parallel models where each worker only needs to
+read its own shard rather than the entire checkpoint.
+
+Example usage:
+
+python save_sharded_state.py \
+    --model /path/to/load \
+    --tensor-parallel-size 8 \
+    --output /path/to/save
+
+Then, the model can be loaded with
+
+llm = LLM(
+    model="/path/to/save",
+    load_format="sharded_state",
+    tensor_parallel_size=8,
+)
+"""
+
+import dataclasses
+import os
+import shutil
+from pathlib import Path
+
+from vllm import LLM, EngineArgs
+from vllm.model_executor.model_loader import ShardedStateLoader
+from vllm.utils.argparse_utils import FlexibleArgumentParser
+
+
+def parse_args():
+    parser = FlexibleArgumentParser()
+    EngineArgs.add_cli_args(parser)
+    parser.add_argument(
+        "--output", "-o", required=True, type=str, help="path to output checkpoint"
+    )
+    parser.add_argument(
+        "--file-pattern",
+        type=str,
+        default=ShardedStateLoader.DEFAULT_PATTERN,
+        help="string pattern of saved filenames",
+    )
+    parser.add_argument(
+        "--max-file-size",
+        type=int,
+        default=5 * 1024**3,
+        help="max size (in bytes) of each safetensors file",
+    )
+    return parser.parse_args()
+
+
+def main(args):
+    engine_args = EngineArgs.from_cli_args(args)
+    if engine_args.enable_lora:
+        raise ValueError("Saving with enable_lora=True is not supported!")
+    model_path = engine_args.model
+    if not Path(model_path).is_dir():
+        raise ValueError("model path must be a local directory")
+    # Create LLM instance from arguments
+    llm = LLM(**dataclasses.asdict(engine_args))
+    # Prepare output directory
+    Path(args.output).mkdir(exist_ok=True)
+    # Dump worker states to output directory
+
+    llm.llm_engine.engine_core.save_sharded_state(
+        path=args.output, pattern=args.file_pattern, max_size=args.max_file_size
+    )
+
+    # Copy metadata files to output directory
+    for file in os.listdir(model_path):
+        if os.path.splitext(file)[1] not in (".bin", ".pt", ".safetensors"):
+            if os.path.isdir(os.path.join(model_path, file)):
+                shutil.copytree(
+                    os.path.join(model_path, file), os.path.join(args.output, file)
+                )
+            else:
+                shutil.copy(os.path.join(model_path, file), args.output)
+
+
+if __name__ == "__main__":
+    args = parse_args()
+    main(args)