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/flashinfer-build.sh

@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+# This script is used to build FlashInfer wheels with AOT kernels
+
+set -ex
+
+# FlashInfer configuration
+FLASHINFER_GIT_REPO="https://github.com/flashinfer-ai/flashinfer.git"
+BUILD_WHEEL="${BUILD_WHEEL:-true}"
+
+if [[ -z "${FLASHINFER_GIT_REF}" ]]; then
+    echo "❌ FLASHINFER_GIT_REF must be specified" >&2
+    exit 1
+fi
+
+if [[ -z "${CUDA_VERSION}" ]]; then
+    echo "❌ CUDA_VERSION must be specified" >&2
+    exit 1
+fi
+
+echo "🏗️  Building FlashInfer ${FLASHINFER_GIT_REF} for CUDA ${CUDA_VERSION}"
+
+# Clone FlashInfer
+git clone --depth 1 --recursive --shallow-submodules \
+    --branch "${FLASHINFER_GIT_REF}" \
+    ${FLASHINFER_GIT_REPO} flashinfer
+
+# Set CUDA arch list based on CUDA version
+# Exclude CUDA arches for older versions (11.x and 12.0-12.7)
+if [[ "${CUDA_VERSION}" == 11.* ]]; then
+    FI_TORCH_CUDA_ARCH_LIST="7.5 8.0 8.9"
+elif [[ "${CUDA_VERSION}" == 12.[0-7]* ]]; then
+    FI_TORCH_CUDA_ARCH_LIST="7.5 8.0 8.9 9.0a"
+elif [[ "${CUDA_VERSION}" == 12.[8-9]* ]]; then
+    # CUDA 12.8–12.9
+    FI_TORCH_CUDA_ARCH_LIST="7.5 8.0 8.9 9.0a 10.0a 10.3a 12.0"
+else
+    # CUDA 13.0+
+    FI_TORCH_CUDA_ARCH_LIST="7.5 8.0 8.9 9.0a 10.0f 12.0"
+fi
+
+echo "🏗️ Building FlashInfer AOT for arches: ${FI_TORCH_CUDA_ARCH_LIST}"
+
+pushd flashinfer
+    # Make sure the wheel is built for the correct CUDA version
+    export UV_TORCH_BACKEND=cu$(echo "$CUDA_VERSION" | cut -d. -f1,2 | tr -d '.')
+
+    # Build AOT kernels
+    export TORCH_CUDA_ARCH_LIST="${FI_TORCH_CUDA_ARCH_LIST}"
+    export FLASHINFER_CUDA_ARCH_LIST="${FI_TORCH_CUDA_ARCH_LIST}"
+    python3 -m flashinfer.aot
+    
+    if [[ "${BUILD_WHEEL}" == "true" ]]; then
+        # Build wheel for distribution
+        uv build --no-build-isolation --wheel --out-dir ../flashinfer-dist .
+        echo "✅ FlashInfer wheel built successfully in flashinfer-dist/"
+    else
+        # Install directly (for Dockerfile)
+        uv pip install --system --no-build-isolation --force-reinstall .
+        echo "✅ FlashInfer installed successfully"
+    fi
+popd
+
+# Cleanup
+rm -rf flashinfer