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/vllm/entrypoints/openai/completion/api_router.py

@@ -0,0 +1,70 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+
+from http import HTTPStatus
+
+from fastapi import APIRouter, Depends, FastAPI, Request
+from fastapi.responses import JSONResponse, StreamingResponse
+
+from vllm.entrypoints.openai.completion.protocol import (
+    CompletionRequest,
+    CompletionResponse,
+)
+from vllm.entrypoints.openai.completion.serving import OpenAIServingCompletion
+from vllm.entrypoints.openai.engine.protocol import ErrorResponse
+from vllm.entrypoints.openai.orca_metrics import metrics_header
+from vllm.entrypoints.openai.utils import validate_json_request
+from vllm.entrypoints.utils import (
+    load_aware_call,
+    with_cancellation,
+)
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
+
+router = APIRouter()
+ENDPOINT_LOAD_METRICS_FORMAT_HEADER_LABEL = "endpoint-load-metrics-format"
+
+
+def completion(request: Request) -> OpenAIServingCompletion | None:
+    return request.app.state.openai_serving_completion
+
+
+@router.post(
+    "/v1/completions",
+    dependencies=[Depends(validate_json_request)],
+    responses={
+        HTTPStatus.OK.value: {"content": {"text/event-stream": {}}},
+        HTTPStatus.BAD_REQUEST.value: {"model": ErrorResponse},
+        HTTPStatus.NOT_FOUND.value: {"model": ErrorResponse},
+        HTTPStatus.INTERNAL_SERVER_ERROR.value: {"model": ErrorResponse},
+    },
+)
+@with_cancellation
+@load_aware_call
+async def create_completion(request: CompletionRequest, raw_request: Request):
+    metrics_header_format = raw_request.headers.get(
+        ENDPOINT_LOAD_METRICS_FORMAT_HEADER_LABEL, ""
+    )
+    handler = completion(raw_request)
+    if handler is None:
+        raise NotImplementedError("The model does not support Completions API")
+
+    generator = await handler.create_completion(request, raw_request)
+
+    if isinstance(generator, ErrorResponse):
+        return JSONResponse(
+            content=generator.model_dump(), status_code=generator.error.code
+        )
+    elif isinstance(generator, CompletionResponse):
+        return JSONResponse(
+            content=generator.model_dump(),
+            headers=metrics_header(metrics_header_format),
+        )
+
+    return StreamingResponse(content=generator, media_type="text/event-stream")
+
+
+def attach_router(app: FastAPI):
+    app.include_router(router)