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/.buildkite/test_areas/models_basic.yaml

@@ -0,0 +1,71 @@
+group: Models - Basic
+depends_on: 
+  - image-build
+steps:
+- label: Basic Models Tests (Initialization)
+  timeout_in_minutes: 45
+  torch_nightly: true
+  source_file_dependencies:
+  - vllm/
+  - tests/models/test_initialization.py
+  - tests/models/registry.py
+  commands:
+    # Run a subset of model initialization tests
+    - pytest -v -s models/test_initialization.py::test_can_initialize_small_subset
+
+- label: Basic Models Tests (Extra Initialization) %N
+  timeout_in_minutes: 45
+  torch_nightly: true
+  source_file_dependencies:
+  - vllm/model_executor/models/
+  - tests/models/test_initialization.py
+  - tests/models/registry.py
+  commands:
+    # Only when vLLM model source is modified - test initialization of a large
+    # subset of supported models (the complement of the small subset in the above
+    # test.) Also run if model initialization test file is modified
+    - pytest -v -s models/test_initialization.py -k 'not test_can_initialize_small_subset' --num-shards=$$BUILDKITE_PARALLEL_JOB_COUNT --shard-id=$$BUILDKITE_PARALLEL_JOB
+  parallelism: 2
+
+- label: Basic Models Tests (Other)
+  timeout_in_minutes: 45
+  source_file_dependencies:
+  - vllm/
+  - tests/models/test_terratorch.py
+  - tests/models/test_transformers.py
+  - tests/models/test_registry.py
+  commands:
+    - pytest -v -s models/test_terratorch.py models/test_transformers.py models/test_registry.py
+  mirror:
+    amd:
+      device: mi325_1
+      depends_on:
+      - image-build-amd
+    
+
+- label: Basic Models Test (Other CPU) # 5min
+  depends_on: 
+  - image-build-cpu
+  timeout_in_minutes: 10
+  source_file_dependencies:
+  - vllm/
+  - tests/models/test_utils.py
+  - tests/models/test_vision.py
+  device: cpu
+  commands:
+    - pytest -v -s models/test_utils.py models/test_vision.py
+
+- label: Transformers Nightly Models
+  working_dir: "/vllm-workspace/"
+  optional: true
+  soft_fail: true
+  commands:
+    - pip install --upgrade git+https://github.com/huggingface/transformers
+    - pytest -v -s tests/models/test_initialization.py
+    - pytest -v -s tests/models/test_transformers.py
+    - pytest -v -s tests/models/multimodal/processing/
+    - pytest -v -s tests/models/multimodal/test_mapping.py
+    - python3 examples/basic/offline_inference/chat.py
+    - python3 examples/offline_inference/vision_language.py --model-type qwen2_5_vl
+    # Whisper needs spawn method to avoid deadlock
+    - VLLM_WORKER_MULTIPROC_METHOD=spawn python3 examples/offline_inference/audio_language.py --model-type whisper