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/cmake/external_projects/qutlass.cmake

@@ -0,0 +1,102 @@
+include(FetchContent)
+
+set(CUTLASS_INCLUDE_DIR "${CUTLASS_INCLUDE_DIR}" CACHE PATH "Path to CUTLASS include/ directory")
+
+if(DEFINED ENV{QUTLASS_SRC_DIR})
+  set(QUTLASS_SRC_DIR $ENV{QUTLASS_SRC_DIR})
+endif()
+
+if(QUTLASS_SRC_DIR)
+  FetchContent_Declare(
+    qutlass
+    SOURCE_DIR ${QUTLASS_SRC_DIR}
+    CONFIGURE_COMMAND ""
+    BUILD_COMMAND ""
+  )
+else()
+  FetchContent_Declare(
+    qutlass
+    GIT_REPOSITORY https://github.com/IST-DASLab/qutlass.git
+    GIT_TAG 830d2c4537c7396e14a02a46fbddd18b5d107c65
+    GIT_PROGRESS TRUE
+    CONFIGURE_COMMAND ""
+    BUILD_COMMAND ""
+  )
+endif()
+
+FetchContent_Populate(qutlass)
+
+if(NOT qutlass_SOURCE_DIR)
+  message(FATAL_ERROR "[QUTLASS] source directory could not be resolved.")
+endif()
+message(STATUS "[QUTLASS] QuTLASS is available at ${qutlass_SOURCE_DIR}")
+
+if(${CMAKE_CUDA_COMPILER_VERSION} VERSION_GREATER_EQUAL 13.0)
+  cuda_archs_loose_intersection(QUTLASS_ARCHS "12.0a;10.0f" "${CUDA_ARCHS}")
+else()
+  cuda_archs_loose_intersection(QUTLASS_ARCHS "12.0a;10.0a;10.3a" "${CUDA_ARCHS}")
+endif()
+
+if(${CMAKE_CUDA_COMPILER_VERSION} VERSION_GREATER_EQUAL 12.8 AND QUTLASS_ARCHS)
+
+  if(QUTLASS_ARCHS MATCHES "10\\.(0a|3a|0f)")
+    set(QUTLASS_TARGET_CC 100)
+  elseif(QUTLASS_ARCHS MATCHES "12\\.0a")
+    set(QUTLASS_TARGET_CC 120)
+  else()
+    message(FATAL_ERROR "[QUTLASS] internal error parsing CUDA_ARCHS='${QUTLASS_ARCHS}'.")
+  endif()
+
+  set(QUTLASS_SOURCES
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/bindings.cpp
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/gemm.cu
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/gemm_ada.cu
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/fused_quantize_mx.cu
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/fused_quantize_nv.cu
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/fused_quantize_mx_sm100.cu
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/fused_quantize_nv_sm100.cu
+  )
+
+  set(QUTLASS_INCLUDES
+    ${qutlass_SOURCE_DIR}
+    ${qutlass_SOURCE_DIR}/qutlass
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/include
+    ${qutlass_SOURCE_DIR}/qutlass/csrc/include/cutlass_extensions
+  )
+
+  if(CUTLASS_INCLUDE_DIR AND EXISTS "${CUTLASS_INCLUDE_DIR}/cutlass/cutlass.h")
+    list(APPEND QUTLASS_INCLUDES "${CUTLASS_INCLUDE_DIR}")
+  elseif(EXISTS "${qutlass_SOURCE_DIR}/qutlass/third_party/cutlass/include/cutlass/cutlass.h")
+    list(APPEND QUTLASS_INCLUDES "${qutlass_SOURCE_DIR}/qutlass/third_party/cutlass/include")
+    message(STATUS "[QUTLASS] Using QuTLASS vendored CUTLASS headers (no vLLM CUTLASS detected).")
+  else()
+    message(FATAL_ERROR "[QUTLASS] CUTLASS headers not found. "
+                        "Set -DCUTLASS_INCLUDE_DIR=/path/to/cutlass/include")
+  endif()
+
+  set_gencode_flags_for_srcs(
+    SRCS "${QUTLASS_SOURCES}"
+    CUDA_ARCHS "${QUTLASS_ARCHS}"
+  )
+
+  target_sources(_C PRIVATE ${QUTLASS_SOURCES})
+  target_include_directories(_C PRIVATE ${QUTLASS_INCLUDES})
+  target_compile_definitions(_C PRIVATE
+    QUTLASS_DISABLE_PYBIND=1
+    TARGET_CUDA_ARCH=${QUTLASS_TARGET_CC}
+  )
+
+  set_property(SOURCE ${QUTLASS_SOURCES} APPEND PROPERTY COMPILE_OPTIONS
+    $<$<COMPILE_LANGUAGE:CUDA>:--expt-relaxed-constexpr --use_fast_math -O3>
+  )
+
+else()
+  if("${CMAKE_CUDA_COMPILER_VERSION}" VERSION_LESS "12.8")
+    message(STATUS
+      "[QUTLASS] Skipping build: CUDA 12.8 or newer is required (found ${CMAKE_CUDA_COMPILER_VERSION}).")
+  else()
+    message(STATUS
+      "[QUTLASS] Skipping build: no supported arch (12.0a / 10.0a) found in "
+      "CUDA_ARCHS='${CUDA_ARCHS}'.")
+  endif()
+endif()