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/samplers/test_logprobs.py

@@ -0,0 +1,91 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+
+from vllm import SamplingParams
+from vllm.logprobs import FlatLogprobs
+
+MODELS = ["distilbert/distilgpt2"]
+MAX_TOKENS = 5
+NUM_TOP_LOGPROBS = 5
+NUM_PROMPT_LOGPROBS = 7
+MAX_LOGPROBS = max(NUM_TOP_LOGPROBS, NUM_PROMPT_LOGPROBS)
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", ["half"])
+@pytest.mark.parametrize("greedy", [True, False])
+@pytest.mark.parametrize("flat_logprobs", [True, False])
+def test_ranks(
+    vllm_runner,
+    model,
+    dtype,
+    greedy,
+    flat_logprobs,
+    example_prompts,
+):
+    with vllm_runner(model, dtype=dtype, max_logprobs=MAX_LOGPROBS) as vllm_model:
+        tokenizer = vllm_model.llm.get_tokenizer()
+        example_prompt_tokens = [tokenizer.encode(prompt) for prompt in example_prompts]
+        sampling_params = SamplingParams(
+            temperature=0.0 if greedy else 1.0,
+            top_p=1.0,
+            max_tokens=MAX_TOKENS,
+            logprobs=NUM_TOP_LOGPROBS,
+            prompt_logprobs=NUM_PROMPT_LOGPROBS,
+            flat_logprobs=flat_logprobs,
+        )
+        results = vllm_model.generate_w_logprobs(example_prompts, sampling_params)
+
+    assert len(results) == len(example_prompt_tokens)
+    for i, (result, prompt_tokens) in enumerate(zip(results, example_prompt_tokens)):
+        decode_tokens, _, decode_logprobs, prompt_logprobs = result
+
+        # Ensure the return type of logprobs is accurate
+        assert isinstance(prompt_logprobs, FlatLogprobs if flat_logprobs else list)
+        assert isinstance(decode_logprobs, FlatLogprobs if flat_logprobs else list)
+
+        ########################
+        # Check prompt logprobs
+        ########################
+        assert len(prompt_tokens) == len(prompt_logprobs)
+        # No logprob for first prompt token
+        assert not prompt_logprobs[0]
+        for position, (token, logprobs) in enumerate(
+            zip(prompt_tokens[1:], prompt_logprobs[1:]), start=1
+        ):
+            # Ensure logprobs of prompt token is always returned
+            logprob = logprobs.get(token)
+            assert logprob is not None
+            assert logprob.rank >= 1
+            # Ensure # of returned logprobs should be
+            # either NUM_PROMPT_LOGPROBS or NUM_PROMPT_LOGPROBS+1
+            assert NUM_PROMPT_LOGPROBS <= len(logprobs) <= NUM_PROMPT_LOGPROBS + 1
+            # Ensure top NUM_PROMPT_LOGPROBS is always extracted
+            assert set(range(1, NUM_PROMPT_LOGPROBS + 1)).issubset(
+                {logprob.rank for logprob in logprobs.values()}
+            )
+
+        ########################
+        # Check sample logprobs
+        ########################
+        assert len(decode_tokens) == len(decode_logprobs)
+        for position, (token, logprobs) in enumerate(
+            zip(decode_tokens, decode_logprobs)
+        ):
+            # Ensure logprobs of chosen token is always returned
+            logprob = logprobs.get(token)
+            assert logprob is not None
+            if greedy:
+                # For greedy sampling, all chosen logprob should be top ranked
+                assert logprob.rank == 1
+            else:
+                assert logprob.rank >= 1
+            # Ensure # of returned logprobs should be
+            # either NUM_TOP_LOGPROBS or NUM_TOP_LOGPROBS+1
+            assert NUM_TOP_LOGPROBS <= len(logprobs) <= NUM_TOP_LOGPROBS + 1
+            # Ensure top NUM_TOP_LOGPROBS logprobs is always extracted
+            assert set(range(1, NUM_TOP_LOGPROBS + 1)).issubset(
+                {logprob.rank for logprob in logprobs.values()}
+            )