fix(moe): guard FP8 delegate activation params (#36275)

Signed-off-by: jikuixie <jikuixie@gmail.com>
Co-authored-by: Mohammad Angkad <mohammad.angkad@radixark.ai>
Co-authored-by: Mohammad Miadh Angkad <176301910+mmangkad@users.noreply.github.com>
Co-authored-by: shyeh25 <206795756+shyeh25@users.noreply.github.com>

python/sglang/srt/layers/quantization/fp8.py

@@ -1085,6 +1085,9 @@ class Fp8MoEMethod(FusedMoEMethodBase):
         self.is_fp4_expert = self.quant_config.is_fp4_experts
         self.dequant_fp4_to_fp8 = self.quant_config.dequant_fp4_to_fp8
         self.with_bias = False
+        # The MxFP4 wrapper methods borrow this instance for weight loading;
+        # they never call create_moe_runner, so moe_runner_config is unset.
+        self._owns_moe_runner = False
         if get_moe_runner_backend().is_cutlass():
             assert (
                 cutlass_fp8_supported()
@@ -2144,10 +2147,12 @@ class Fp8MoEMethod(FusedMoEMethodBase):
 
                 align_fp8_moe_weights_for_flashinfer_trtllm(layer)
 
+        # The runner backend is global, so it is also true for a borrowed delegate,
+        # which has no moe_runner_config and whose kernel ignores these params.
         if (
             get_moe_runner_backend().is_flashinfer_trtllm()
             or get_moe_runner_backend().is_flashinfer_trtllm_routed()
-        ):
+        ) and self._owns_moe_runner:
             self._prepare_flashinfer_trtllm_activation_params(layer)
 
         if get_moe_runner_backend().is_hpc_ops():
@@ -2325,6 +2330,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
     def create_moe_runner(
         self, layer: torch.nn.Module, moe_runner_config: MoeRunnerConfig
     ):
+        self._owns_moe_runner = False
         self.moe_runner_config = moe_runner_config
         moe_runner_backend = get_moe_runner_backend()
 
@@ -2349,6 +2355,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             or moe_runner_backend.is_hpc_ops()
         ):
             self.runner = MoeRunner(moe_runner_backend, moe_runner_config)
+            self._owns_moe_runner = True
         else:
             # TODO(cwan): refactor other backends
             pass