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/tools/install_gdrcopy.sh

@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Usage: install_gdrcopy.sh <GDRCOPY_OS_VERSION> <GDRCOPY_CUDA_VERSION> <uuarch>
+# uuarch must be "x64" or "aarch64"
+# Optional: set GDRCOPY_VERSION to override the libgdrapi package version (default: 2.5.1-1)
+# Requires: curl, apt-get, root privileges
+if [[ $(id -u) -ne 0 ]]; then
+  echo "Must be run as root" >&2
+  exit 1
+fi
+if [[ $# -ne 3 ]]; then
+  echo "Usage: $0 <GDRCOPY_OS_VERSION> <GDRCOPY_CUDA_VERSION> <uuarch(x64|aarch64)>" >&2
+  exit 1
+fi
+OS_VER="$1"
+CUDA_VER="$2"
+UUARCH_RAW="$3"
+# Normalize/validate arch
+case "${UUARCH_RAW,,}" in
+  aarch64|arm64)
+    URL_ARCH="aarch64"
+    DEB_ARCH="arm64"
+    ;;
+  x64|x86_64|amd64)
+    URL_ARCH="x64"
+    DEB_ARCH="amd64"
+    ;;
+  *)
+    echo "Unsupported uuarch: ${UUARCH_RAW}. Use 'x64' or 'aarch64'." >&2
+    exit 1
+    ;;
+esac
+
+OS_VER_LOWER="$(tr '[:upper:]' '[:lower:]' <<<"$OS_VER")"
+GDRCOPY_PKG_VER="${GDRCOPY_VERSION:-2.5.1-1}"
+
+DEB_NAME="libgdrapi_${GDRCOPY_PKG_VER}_${DEB_ARCH}.${OS_VER}.deb"
+BASE_URL="https://developer.download.nvidia.com/compute/redist/gdrcopy"
+URL="${BASE_URL}/CUDA%20${CUDA_VER}/${OS_VER_LOWER}/${URL_ARCH}/${DEB_NAME}"
+
+echo "Downloading: ${URL}"
+TMPDIR="$(mktemp -d)"
+trap 'rm -rf "${TMPDIR}"' EXIT
+
+curl -fSL "${URL}" -o "${TMPDIR}/${DEB_NAME}"
+
+export DEBIAN_FRONTEND=noninteractive
+apt-get update
+apt-get install -y "${TMPDIR}/${DEB_NAME}"
+apt-get clean
+rm -rf /var/lib/apt/lists/*
+
+echo "Installed ${DEB_NAME}"