sync: rebase PR 8165 routing fix onto current main

[haic0]

Purpose

Update fix/amd-ulysses-multigpu-routing from its current acda42f7 history to current upstream main (4af28f33) while preserving only the original vllm-project#8165 routing delta.

The helper head is one signed-off commit atop current main. It therefore includes the merged Wan BF16 fix vllm-project#8188 and Hunyuan CPU-dispatch fix vllm-project#8166 that address the unrelated AMD failures on the old vllm-project#8165 head.

This is a coordination PR into the existing author branch, not a duplicate upstream PR.

Validation

• .venv/bin/python -m pytest -q -o addopts= --confcutdir=tests/buildkite tests/buildkite/test_amd_pipeline.py — 11 passed
• Both changed AMD YAML pipelines parsed with yaml.safe_load
• pre-commit run --files for all three changed files — passed, including Buildkite validation
• git diff --check origin/main...HEAD — passed
• DCO trailer present

AI assistance was used to investigate the CI failures, prepare the rebase helper, and run validation. The branch owner should review the resulting history before merging.

[haic0]

Superseded: the validated rebase was pushed directly to fix/amd-ulysses-multigpu-routing as 9452e39c423a08793fadca705b85437d2c699301 using an exact force-with-lease against 9208762db9a370f59a42e8a66620956cd6c11c33. Upstream PR vllm-project#8165 now points to the direct-push head, so this helper PR must not be merged.