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/tests/compile/fullgraph/test_multimodal_compile.py

@@ -0,0 +1,110 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import pytest
+
+from vllm.compilation.counter import compilation_counter
+from vllm.config import VllmConfig
+from vllm.config.compilation import CompilationMode
+from vllm.platforms import current_platform
+
+
+def test_compile():
+    vllm_config = VllmConfig()
+    # Default configuration does not compile mm encoder
+    assert not vllm_config.compilation_config.compile_mm_encoder
+
+
+# forked needed to workaround https://github.com/vllm-project/vllm/issues/21073
+@pytest.mark.forked
+@pytest.mark.skipif(not current_platform.is_cuda(), reason="Skip if not cuda")
+def test_qwen2_5_vl_compilation(vllm_runner, monkeypatch):
+    """Test that Qwen2.5-VL vision submodules are compiled.
+
+    This test verifies that the 3 vision submodules (Qwen2_5_VisionPatchEmbed,
+    Qwen2_5_VisionBlock, and Qwen2_5_VisionPatchMerger) are properly tagged
+    for compilation by checking that num_models_seen increases by at least 3.
+    """
+    # Disable multiprocessing so that the counter is in the same process
+    monkeypatch.setenv("VLLM_ENABLE_V1_MULTIPROCESSING", "0")
+
+    with (
+        # NOTE: Qwen2.5-VL has 35 models in total - the LLM backend
+        # Vision Patch Embed, Vision Patch Merger, and then 32 Vision Blocks
+        # (one for each layer) - in the future, we should fix vLLM compilation
+        # logic to handle this case and only compile the Vision submodules once
+        # and reuse the compiled code for all layers
+        # See https://github.com/vllm-project/vllm/issues/27590
+        compilation_counter.expect(num_models_seen=35),
+        vllm_runner(
+            "Qwen/Qwen2.5-VL-3B-Instruct",
+            max_model_len=2048,
+            gpu_memory_utilization=0.8,
+            compilation_config={
+                "mode": CompilationMode.VLLM_COMPILE,
+                "compile_mm_encoder": True,
+            },
+        ) as _,
+    ):
+        pass
+
+
+# forked needed to workaround https://github.com/vllm-project/vllm/issues/21073
+@pytest.mark.forked
+@pytest.mark.skipif(not current_platform.is_cuda(), reason="Skip if not cuda")
+def test_qwen2_5_vl_no_vit_compilation(vllm_runner, monkeypatch):
+    """Test that Qwen2.5-VL vision submodules are not compiled when the
+    config is passed off
+    """
+    # Disable multiprocessing so that the counter is in the same process
+    monkeypatch.setenv("VLLM_ENABLE_V1_MULTIPROCESSING", "0")
+
+    with (
+        compilation_counter.expect(num_models_seen=1),
+        vllm_runner(
+            "Qwen/Qwen2.5-VL-3B-Instruct",
+            max_model_len=2048,
+            gpu_memory_utilization=0.8,
+            compilation_config={
+                "mode": CompilationMode.VLLM_COMPILE,
+                "compile_mm_encoder": False,
+            },
+        ) as _,
+    ):
+        pass
+
+
+# forked needed to workaround https://github.com/vllm-project/vllm/issues/21073
+# Requires Cuda and 8 gpus as well
+@pytest.mark.forked
+@pytest.mark.skip(reason="Skipping due to CI resource constraints")
+def test_mllama4_vit_compilation(vllm_runner, monkeypatch):
+    """Test that Mllama4 vision submodules are compiled.
+
+    This test verifies that the 2 vision submodules (Llama4VisionEncoder,
+    Llama4VisionPixelShuffleMLP) are properly tagged
+    for compilation by checking that num_models_seen increases to 3.
+
+    However since we are using TP=8, we compilation_counter will not
+    work properly so we will just check the run succeeds rn
+    """
+    # Disable multiprocessing so that the counter is in the same process
+    monkeypatch.setenv("VLLM_ENABLE_V1_MULTIPROCESSING", "0")
+
+    with (
+        monkeypatch.context(),
+        # TODO: Since we require TP=8, this messes with the compilation
+        # counter. We should fix this in the future, but leave for now
+        # to make sure that compilation runs (no crash) with llama vision encoder
+        compilation_counter.expect(num_models_seen=0),
+        vllm_runner(
+            "meta-llama/Llama-4-Scout-17B-16E-Instruct",
+            max_model_len=512,
+            gpu_memory_utilization=0.8,
+            tensor_parallel_size=8,
+            compilation_config={
+                "mode": CompilationMode.VLLM_COMPILE,
+                "compile_mm_encoder": True,
+            },
+        ),
+    ):
+        pass