Changelog

[Unreleased]

Tarjan's SCC algorithm (tarjan_scc.hpp) — single-pass O(V+E) strongly connected components using iterative DFS with low-link values; no transpose graph needed
17 new Tarjan SCC tests (test_tarjan_scc.cpp)
Mapped (sparse) graph algorithm support — all 14 algorithms now accept adjacency_list<G> (both index and map-based containers)
mapped_vertex_range, mapped_adjacency_list, mapped_bidirectional_adjacency_list concepts
vertex_property_map<G, T> type alias and make_vertex_property_map factory (vector for index graphs, unordered_map for mapped)
vertex_property_map_for<M, G> concept for algorithm parameter constraints
vertex_property_map_value_t<Container> trait for extracting per-vertex value types
is_sparse_vertex_container_v<G> trait for compile-time graph type dispatch
Map-based graph test fixtures (map_graph_fixtures.hpp) with sparse vertex IDs
456 new algorithm tests for sparse graph types (4343 → 4799)

edge_descriptor simplified to iterator-only storage — removed the conditional_t<random_access_iterator, size_t, EdgeIter> dual-storage path; edges always store the iterator directly since edges always have physical containers. Eliminates 38 if constexpr branches across 6 files (~500 lines removed).
compressed_graph::vertices(g) returns iota_view — simplified to std::ranges::iota_view<size_t, size_t>(0, num_vertices()), which the vertices CPO wraps automatically via _wrap_if_needed.
vertex_descriptor_view CTAD deduction guides — updated from Container::iterator/const_iterator to std::ranges::iterator_t<> for compatibility with views like iota_view.
edge_descriptor_view forward_list compatibility — fixed constructor to use if constexpr for sized_range check so std::ranges::size() is not compiled for non-sized ranges like forward_list.
All algorithms relaxed from index_adjacency_list<G> to adjacency_list<G>
Algorithm internal arrays use make_vertex_property_map (vector or unordered_map depending on graph type)
User-facing Distances, Predecessors, Weight, Component, Label parameters accept vertex property maps
Index-based for-loops replaced with views::basic_vertexlist(g) iteration
Validation uses if constexpr (index_vertex_range<G>) for size checks, find_vertex for mapped graphs

Bidirectional edge access — in_edges, in_degree, find_in_edge, contains_in_edge CPOs
bidirectional_adjacency_list concept
in_edge_range_t<G>, in_edge_iterator_t<G>, in_edge_t<G> type aliases
out_edge_accessor / in_edge_accessor stateless edge-access policies (edge_accessor.hpp)
in_incidence and in_neighbors views with pipe-syntax adaptors
Accessor template parameter on BFS, DFS, and topological sort views for reverse traversal
dynamic_graph Bidirectional template parameter for incoming-edge lists
undirected_adjacency_list bidirectional support (incoming = outgoing)
Kosaraju SCC algorithm and transpose_graph view
144 new tests (4261 → 4405)
New documentation: bidirectional access tutorial, updated views/concepts/CPO/container docs