ref(upstream): FULL TREE — Deep-Spark xllm (1470) + ds_vllm csrc/models (703)

Replaces cherry-picked upstream_ref with complete source trees.

xllm/ — Iluvatar official C++ inference engine (15MB, 1470 files)
  Complete: kernels → layers → models → runtime → scheduler → api
  Excluded: .git, binary images, third_party submodule checkouts

ds_vllm/ — Iluvatar official vllm fork (8MB, 703 files)
  Included: csrc/ (ALL CUDA kernels), fused_moe/, qwen3_5 model, _custom_ops
  Excluded: tests, benchmarks, docs, examples (not needed for reference)

Critical call chains now fully traceable:
  MoE: moe_topk_softmax_kernels.cuh → ixformer.h → fused_moe.cpp → layer
  GDN: qwen3_gated_delta_net_base.cpp → qwen3_5_gated_delta_net.cpp
  Attention: ixformer.h → xllm_paged_attention → attention.cpp

upstream_ref/xllm/.agents/skills/add-unit-test/SKILL.md

@@ -0,0 +1,48 @@
+---
+name: add-unit-test
+description: Add or update xLLM unit tests in the repository. Use when Codex needs to create a new C++/CUDA/NPU/MLU unit test, place a test under tests/, wire it into CMake with cc_test, update an existing test target, choose platform gates, or validate test naming and dependencies against current xLLM test conventions.
+---
+
+# Add Unit Test
+
+## Workflow
+
+1. Inspect the production code and the nearest existing tests before writing a new test.
+   - Match the production path under `xllm/` to `tests/` where possible.
+   - Prefer extending an existing nearby `*_test.cpp` and `cc_test` target when the behavior belongs to the same domain.
+   - Create a new test source only when it improves isolation, keeps platform setup separate, or follows an existing directory pattern.
+
+2. Read the project style guide before editing production files under `xllm/`, and apply the same C++ style discipline to new test code:
+   `.agents/skills/code-review/references/custom-code-style.md`.
+
+3. Follow the current test layout and CMake conventions.
+   - Read [xllm-test-patterns.md](references/xllm-test-patterns.md) when adding a new test file, new `cc_test`, platform-specific test, or test directory.
+   - Use `*_test.cpp` for C++ test files and `*_test.cu` for CUDA source tests.
+   - Do not create nested `test/` or `tests/` directories for new unit tests unless the surrounding tree already requires that structure.
+
+4. Wire tests through CMake with `include(cc_test)` and `cc_test(...)`.
+   - Keep source names relative to the current test directory unless an existing target already uses an absolute source path for a production `.cpp`.
+   - Use target names ending in `_test`.
+   - Put platform-directory gates in the parent `CMakeLists.txt` when the whole child directory is platform-specific.
+   - Use target-level `if(USE_NPU)`, `if(USE_MLU)`, `if(USE_CUDA)`, or generator expressions only when a mixed directory contains both generic and platform-specific tests.
+
+5. Write tests for observable behavior, not implementation trivia.
+   - Cover success, edge, and error paths touched by the change.
+   - Prefer deterministic inputs, fixed seeds, and small tensors/data structures.
+   - Keep helpers file-local in an anonymous namespace unless shared by multiple test files.
+   - Use `TEST`/`TEST_F` names that describe behavior clearly.
+
+6. Validate narrowly before finishing.
+   - Always run `git diff --check` for the changed test paths.
+   - Search for stale filenames after moving or renaming tests.
+   - Run the narrowest build/test command available locally; if not feasible, state the exact reason and what was checked instead.
+
+## Common Commands
+
+```bash
+rg --files tests/<area>
+rg "old_test_name|old_file_name" tests xllm CMakeLists.txt
+git diff --check -- tests/<area>
+```
+
+For full remote validation on the development machine, use the repository AGENTS instructions for SSH, container, build, and test commands.