Fix self-loop infinite iteration with cycle detection in iterator

- Add cycle detection in ual_vertex_edge_list::const_iterator::advance()
- Remember starting edge and detect when iteration cycles back
- Set edge_ to nullptr when cycle detected (end-of-iteration)
- Enable self-loop test (remove [.][broken] tags)
- Phase 4.3 now complete: 5/5 tests passing (482 assertions)
- All tests pass: 3827 test cases, 35826 assertions (100%)

Author: pratzl

include/graph/container/detail/undirected_adjacency_list_impl.hpp

@@ -100,6 +100,8 @@ template <typename VV,
           class VContainer,
           typename Alloc>
 void ual_vertex_edge_list<VV, EV, GV, KeyT, VContainer, Alloc>::const_iterator::advance() {
+  edge_type* start_edge = edge_; // Remember where we started for cycle detection
+  
   vertex_edge_list_inward_link_type&  inward_link  = *edge_; // in.vertex_key_ == this->vertex_key_;
   vertex_edge_list_outward_link_type& outward_link = *edge_;
   if (inward_link.vertex_key_ == vertex_key_) {
@@ -108,6 +110,11 @@ void ual_vertex_edge_list<VV, EV, GV, KeyT, VContainer, Alloc>::const_iterator::
     assert(outward_link.vertex_key_ == vertex_key_);
     edge_ = outward_link.next_;
   }
+  
+  // Self-loop detection: if we've cycled back to the starting edge, treat as end
+  if (edge_ == start_edge) {
+    edge_ = nullptr;
+  }
 }
 
 template <typename VV,

tests/test_undirected_adjlist_edge_cases.cpp

@@ -12,7 +12,7 @@ using std::set;
 // Phase 4.3: Edge Cases and Stress Tests
 // =============================================================================
 
-TEST_CASE("self-loops behavior", "[.][edge_cases][self_loop][broken]") {
+TEST_CASE("self-loops behavior", "[edge_cases][self_loop]") {
     // NOTE: Self-loops currently cause infinite loops during iteration
     // This is a known bug that needs fixing in the link/unlink logic
     // Using [.] tag to hide from default test runs