[Bugfix][HiSparse] Resolve MTP verification rows with a union residency kernel

csrc/libtorch_stable/ops.h

@@ -680,7 +680,7 @@ void hisparse_resolve_residency(
     torch::stable::Tensor& device_global_indices,
     torch::stable::Tensor& lru_slots,
     std::optional<torch::stable::Tensor> const& request_state_indices,
-    int64_t region_stride,
+    int64_t region_stride, int64_t max_union_rows,
     std::optional<torch::stable::Tensor> const& miss_mask,
     std::optional<torch::stable::Tensor> const& stats,
     std::optional<torch::stable::Tensor> const& attention_indices,

csrc/libtorch_stable/torch_bindings.cpp

@@ -995,6 +995,7 @@ STABLE_TORCH_LIBRARY_FRAGMENT(_C_cache_ops, ops) {
       "                 Tensor! lru_slots,"
       "                 Tensor? request_state_indices,"
       "                 int region_stride,"
+      "                 int max_union_rows,"
       "                 Tensor(a!)? miss_mask=None,"
       "                 Tensor(b!)? stats=None,"
       "                 Tensor(c!)? attention_indices=None,"

docs/design/hisparse.md

@@ -130,10 +130,10 @@ path. The resolver consumes the existing graph-stable request mapping from
 attention metadata; neither the worker nor individual cache handles keep a
 duplicate mapping.
 
-Speculative decoding resolves and consumes each verification step in order.
-Each step receives distinct replayable plan rows while sharing the request's
-hot-cache state, so a later step cannot reuse a hot row before an earlier step
-has consumed it.
+Speculative decoding resolves all verification rows of a request in one pass:
+one block resolves the union of the rows' top-k against the request's hot-cache
+state, so rows that select the same host row share its hot row and no row
+evicts a hot row another row of the step still reads.
 
 ## P/D import target