fix: wire MoE topk via ixformer C++ bridge + disable broken flash_qla GDN
Two call chain breaks fixed:
1. MoE routing (2304 calls/token):
BEFORE: torch.softmax + torch.topk (3 Python GPU ops, no ixformer)
AFTER: ix_bridge.py → ix_moe_bridge.cpp → ixformer::infer::topk_softmax()
Source: upstream_ref/xllm/xllm/core/kernels/ilu/fused_moe.cpp line 46
The C++ API exists in base image SDK (ixformer.h declares it),
only the Python binding (ixformer.functions) was missing.
2. GDN prefill (4 layers, 99.98% NaN):
BEFORE: flash_qla SM70 kernel → abs mean=inf → nan_to_num → zeros
AFTER: skip flash_qla, use _pytorch_forward directly
Source: upstream_ref/xllm qwen3_gated_delta_net_base.cpp uses
identical PyTorch chunked logic (no flash_qla).
Sub168 (working build) never deployed flash_qla either.
Files:
- ex_engine/csrc/ix_moe_bridge.cpp: torch C++ extension calling ixformer C++ API
- ex_engine/python/ix_bridge.py: JIT-compile loader with PyTorch fallback
- qwen3_5.py: import ix_bridge for MoE, disable flash_qla for GDN
- patch_ops.sh: deploy ix_bridge .cpp + .py into vllm model dir
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