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/multimodal/test_image.py

@@ -0,0 +1,40 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from pathlib import Path
+
+import numpy as np
+import pytest
+from PIL import Image, ImageChops
+
+from vllm.multimodal.image import convert_image_mode
+
+pytestmark = pytest.mark.cpu_test
+
+ASSETS_DIR = Path(__file__).parent / "assets"
+assert ASSETS_DIR.exists()
+
+
+def test_rgb_to_rgb():
+    # Start with an RGB image.
+    original_image = Image.open(ASSETS_DIR / "image1.png").convert("RGB")
+    converted_image = convert_image_mode(original_image, "RGB")
+
+    # RGB to RGB should be a no-op.
+    diff = ImageChops.difference(original_image, converted_image)
+    assert diff.getbbox() is None
+
+
+def test_rgba_to_rgb():
+    original_image = Image.open(ASSETS_DIR / "rgba.png")
+    original_image_numpy = np.array(original_image)
+
+    converted_image = convert_image_mode(original_image, "RGB")
+    converted_image_numpy = np.array(converted_image)
+
+    for i in range(original_image_numpy.shape[0]):
+        for j in range(original_image_numpy.shape[1]):
+            # Verify that all transparent pixels are converted to white.
+            if original_image_numpy[i][j][3] == 0:
+                assert converted_image_numpy[i][j][0] == 255
+                assert converted_image_numpy[i][j][1] == 255
+                assert converted_image_numpy[i][j][2] == 255