diff --git a/network_process/src/prim_gen/filter_tet_by_subface.cpp b/network_process/src/prim_gen/filter_tet_by_subface.cpp
index 5b04291..8067722 100644
--- a/network_process/src/prim_gen/filter_tet_by_subface.cpp
+++ b/network_process/src/prim_gen/filter_tet_by_subface.cpp
@@ -71,6 +71,10 @@ void filter_tet_by_subface(const btree_map_mp<uint32_t, stl_vector_mp<uint32_t>>
     tetrahedron_active_subface_start_index.reserve(tetrahedrons.size() + 1);
     active_subface_indices.reserve(tetrahedrons.size());
     tetrahedron_active_subface_start_index.emplace_back(0);
+
+    flat_hash_map_mp<uint32_t, uint32_t> old_to_new_tet_idx{};
+    old_to_new_tet_idx.reserve(tetrahedrons.size() / 4);
+
     for (auto i = 0; i < tetrahedrons.size(); ++i) {
         const auto& tet_info = sign_counts[i];
         for (auto j = 0; j < tet_info.size(); ++j) {
@@ -78,6 +82,8 @@ void filter_tet_by_subface(const btree_map_mp<uint32_t, stl_vector_mp<uint32_t>>
             if ((sign & 0x0F) < 4 && (sign >> 4) < 4) { active_subface_indices.emplace_back(j); }
         }
         if (active_subface_indices.size() > tetrahedron_active_subface_start_index.back()) {
+            // Record mapping BEFORE emplace_back so filtered_tets.size() is the new index.
+            old_to_new_tet_idx[static_cast<uint32_t>(i)] = static_cast<uint32_t>(filtered_tets.size());
             tetrahedron_active_subface_start_index.emplace_back(active_subface_indices.size());
             const auto& vertices = filtered_tets.emplace_back(std::move(tetrahedrons[i]));
             filtered_active_vertices.insert(filtered_active_vertices.end(), vertices.begin(), vertices.end());
@@ -88,6 +94,31 @@ void filter_tet_by_subface(const btree_map_mp<uint32_t, stl_vector_mp<uint32_t>>
     filtered_active_vertices.shrink_to_fit();
     std::swap(filtered_tets, tetrahedrons);
 
+    // Remap zero_vertex_to_incident_tet_mapping: replace every stored original tet
+    // index with its new compact index, and drop indices for tets that were filtered out.
+    // The list must remain sorted (set_intersection is used on it later).
+    for (auto& [vertex_idx, tet_list] : zero_vertex_to_incident_tet_mapping) {
+        stl_vector_mp<uint32_t> updated;
+        updated.reserve(tet_list.size());
+        for (const auto old_idx : tet_list) {
+            auto it = old_to_new_tet_idx.find(old_idx);
+            if (it != old_to_new_tet_idx.end()) { updated.push_back(it->second); }
+        }
+        // The mapping is order-preserving (filtered tets keep their relative order),
+        // so updated is already sorted, but sort explicitly for safety.
+        std::sort(updated.begin(), updated.end());
+        tet_list = std::move(updated);
+    }
+    // Remove entries whose every incident tet was filtered out — they can no longer
+    // contribute to any chain and would cause .at() failures if looked up.
+    for (auto it = zero_vertex_to_incident_tet_mapping.begin(); it != zero_vertex_to_incident_tet_mapping.end();) {
+        if (it->second.empty()) {
+            it = zero_vertex_to_incident_tet_mapping.erase(it);
+        } else {
+            ++it;
+        }
+    }
+
     // change vertex adjacency with filtered vertices, so that each vertex pair in adjacency map is connected directly
     // without any intermediate vertices
     std::sort(filtered_active_vertices.begin(), filtered_active_vertices.end());