BSP: add room adjacency graph for corridor generation (closes #210)

New features:
- bsp.adjacency[i] returns tuple of neighbor leaf indices
- bsp.get_leaf(index) returns BSPNode by leaf index (O(1) lookup)
- node.leaf_index returns this leaf's index (0..n-1) or None
- node.adjacent_tiles[j] returns tuple of Vector wall tiles bordering neighbor j

Implementation details:
- Lazy-computed adjacency cache with generation-based invalidation
- O(n²) pairwise adjacency check on first access
- Wall tiles computed per-direction (not symmetric) for correct perspective
- Supports 'in' operator: `5 in leaf.adjacent_tiles`

Code review fixes applied:
- split_once now increments generation to invalidate cache
- Wall tile cache uses (self, neighbor) key, not symmetric
- Added sq_contains for 'in' operator support
- Documented wall tile semantics (tiles on THIS leaf's boundary)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/McRFPy_API.cpp

@@ -441,6 +441,8 @@ PyObject* PyInit_mcrfpy()
         /*BSP internal types - returned by BSP methods but not directly instantiable*/
         &mcrfpydef::PyBSPNodeType,
         &mcrfpydef::PyBSPIterType,
+        &mcrfpydef::PyBSPAdjacencyType,      // #210: BSP.adjacency wrapper
+        &mcrfpydef::PyBSPAdjacentTilesType,  // #210: BSPNode.adjacent_tiles wrapper
 
         nullptr};
     

src/PyBSP.cpp

@@ -3,9 +3,11 @@
 #include "McRFPy_Doc.h"
 #include "PyPositionHelper.h"
 #include "PyHeightMap.h"
+#include "PyVector.h"  // #210: For wall tile Vectors
 #include <sstream>
 #include <cstdlib>
 #include <ctime>
+#include <algorithm>  // #210: For std::min, std::max
 
 // Static storage for Traversal enum
 PyObject* PyTraversal::traversal_enum_class = nullptr;
@@ -19,6 +21,127 @@ enum TraversalOrder {
     TRAVERSAL_INVERTED_LEVEL_ORDER = 4,
 };
 
+// ==================== Adjacency Helpers (#210) ====================
+
+// Check if two BSP leaf nodes share a wall segment (not just a corner)
+static bool are_adjacent(TCOD_bsp_t* a, TCOD_bsp_t* b) {
+    // a is left of b (vertical wall)
+    if (a->x + a->w == b->x) {
+        int overlap = std::min(a->y + a->h, b->y + b->h) - std::max(a->y, b->y);
+        if (overlap > 0) return true;
+    }
+    // b is left of a (vertical wall)
+    if (b->x + b->w == a->x) {
+        int overlap = std::min(a->y + a->h, b->y + b->h) - std::max(a->y, b->y);
+        if (overlap > 0) return true;
+    }
+    // a is above b (horizontal wall)
+    if (a->y + a->h == b->y) {
+        int overlap = std::min(a->x + a->w, b->x + b->w) - std::max(a->x, b->x);
+        if (overlap > 0) return true;
+    }
+    // b is above a (horizontal wall)
+    if (b->y + b->h == a->y) {
+        int overlap = std::min(a->x + a->w, b->x + b->w) - std::max(a->x, b->x);
+        if (overlap > 0) return true;
+    }
+    return false;
+}
+
+// Compute wall tiles for two adjacent leaves (from perspective of node a).
+// Returns coordinates of tiles on a's boundary that are suitable for corridor placement.
+// For a vertical wall (a left of b): returns a's rightmost column in the overlap range.
+// For a horizontal wall (a above b): returns a's bottommost row in the overlap range.
+// These are the tiles INSIDE leaf a that touch leaf b's boundary.
+static std::vector<sf::Vector2i> compute_wall_tiles(TCOD_bsp_t* a, TCOD_bsp_t* b) {
+    std::vector<sf::Vector2i> tiles;
+
+    // a is left of b (vertical wall at right edge of a)
+    if (a->x + a->w == b->x) {
+        int y_start = std::max(a->y, b->y);
+        int y_end = std::min(a->y + a->h, b->y + b->h);
+        int x = a->x + a->w - 1;  // Last column of a
+        for (int y = y_start; y < y_end; y++) {
+            tiles.push_back({x, y});
+        }
+        return tiles;
+    }
+    // b is left of a (vertical wall at left edge of a)
+    if (b->x + b->w == a->x) {
+        int y_start = std::max(a->y, b->y);
+        int y_end = std::min(a->y + a->h, b->y + b->h);
+        int x = a->x;  // First column of a
+        for (int y = y_start; y < y_end; y++) {
+            tiles.push_back({x, y});
+        }
+        return tiles;
+    }
+    // a is above b (horizontal wall at bottom edge of a)
+    if (a->y + a->h == b->y) {
+        int x_start = std::max(a->x, b->x);
+        int x_end = std::min(a->x + a->w, b->x + b->w);
+        int y = a->y + a->h - 1;  // Last row of a
+        for (int x = x_start; x < x_end; x++) {
+            tiles.push_back({x, y});
+        }
+        return tiles;
+    }
+    // b is above a (horizontal wall at top edge of a)
+    if (b->y + b->h == a->y) {
+        int x_start = std::max(a->x, b->x);
+        int x_end = std::min(a->x + a->w, b->x + b->w);
+        int y = a->y;  // First row of a
+        for (int x = x_start; x < x_end; x++) {
+            tiles.push_back({x, y});
+        }
+        return tiles;
+    }
+
+    return tiles;  // Empty if not adjacent
+}
+
+// Rebuild the adjacency cache for a BSP tree
+static void rebuild_adjacency_cache(PyBSPObject* self) {
+    // Delete old cache if exists
+    if (self->adjacency_cache) {
+        delete self->adjacency_cache;
+    }
+
+    self->adjacency_cache = new BSPAdjacencyCache();
+    self->adjacency_cache->generation = self->generation;
+
+    // Collect all leaves in level-order
+    TCOD_bsp_traverse_level_order(self->root, [](TCOD_bsp_t* node, void* data) -> bool {
+        auto cache = (BSPAdjacencyCache*)data;
+        if (TCOD_bsp_is_leaf(node)) {
+            int idx = (int)cache->leaf_pointers.size();
+            cache->leaf_pointers.push_back(node);
+            cache->ptr_to_index[node] = idx;
+            cache->graph.push_back({});  // Empty neighbor list
+        }
+        return true;
+    }, self->adjacency_cache);
+
+    // Build adjacency graph (O(n^2) pairwise check)
+    auto& cache = *self->adjacency_cache;
+    int n = (int)cache.leaf_pointers.size();
+    for (int i = 0; i < n; i++) {
+        for (int j = i + 1; j < n; j++) {
+            if (are_adjacent(cache.leaf_pointers[i], cache.leaf_pointers[j])) {
+                cache.graph[i].push_back(j);
+                cache.graph[j].push_back(i);
+            }
+        }
+    }
+}
+
+// Ensure adjacency cache is valid, rebuild if needed
+static void ensure_adjacency_cache(PyBSPObject* self) {
+    if (!self->adjacency_cache || self->adjacency_cache->generation != self->generation) {
+        rebuild_adjacency_cache(self);
+    }
+}
+
 // ==================== Traversal Enum ====================
 
 PyObject* PyTraversal::create_enum_class(PyObject* module) {
@@ -193,6 +316,8 @@ PyGetSetDef PyBSP::getsetters[] = {
      MCRF_PROPERTY(size, "Dimensions (width, height). Read-only."), NULL},
     {"root", (getter)PyBSP::get_root, NULL,
      MCRF_PROPERTY(root, "Reference to the root BSPNode. Read-only."), NULL},
+    {"adjacency", (getter)PyBSP::get_adjacency, NULL,
+     MCRF_PROPERTY(adjacency, "Leaf adjacency graph. adjacency[i] returns tuple of neighbor indices. Read-only."), NULL},
     {NULL}
 };
 
@@ -268,6 +393,16 @@ PyMethodDef PyBSP::methods[] = {
          MCRF_ARG("value", "Value inside selected regions. Default: 1.0.")
          MCRF_RETURNS("HeightMap with selected regions filled")
      )},
+    {"get_leaf", (PyCFunction)PyBSP::get_leaf, METH_VARARGS | METH_KEYWORDS,
+     MCRF_METHOD(BSP, get_leaf,
+         MCRF_SIG("(index: int)", "BSPNode"),
+         MCRF_DESC("Get a leaf node by its index (0 to len(bsp)-1). "
+                   "This is useful when working with adjacency data, which returns leaf indices."),
+         MCRF_ARGS_START
+         MCRF_ARG("index", "Leaf index (0 to len(bsp)-1). Negative indices supported.")
+         MCRF_RETURNS("BSPNode at the specified index")
+         MCRF_RAISES("IndexError", "If index is out of range")
+     )},
     {NULL}
 };
 
@@ -283,6 +418,7 @@ PyObject* PyBSP::pynew(PyTypeObject* type, PyObject* args, PyObject* kwds)
         self->orig_w = 0;
         self->orig_h = 0;
         self->generation = 0;
+        self->adjacency_cache = nullptr;  // #210: Lazy-computed
     }
     return (PyObject*)self;
 }
@@ -330,6 +466,12 @@ int PyBSP::init(PyBSPObject* self, PyObject* args, PyObject* kwds)
         TCOD_bsp_delete(self->root);
     }
 
+    // Clean up any existing adjacency cache (#210)
+    if (self->adjacency_cache) {
+        delete self->adjacency_cache;
+        self->adjacency_cache = nullptr;
+    }
+
     // Create new BSP with size
     self->root = TCOD_bsp_new_with_size(x, y, w, h);
     if (!self->root) {
@@ -349,6 +491,11 @@ int PyBSP::init(PyBSPObject* self, PyObject* args, PyObject* kwds)
 
 void PyBSP::dealloc(PyBSPObject* self)
 {
+    // Clean up adjacency cache (#210)
+    if (self->adjacency_cache) {
+        delete self->adjacency_cache;
+        self->adjacency_cache = nullptr;
+    }
     if (self->root) {
         TCOD_bsp_delete(self->root);
         self->root = nullptr;
@@ -422,6 +569,29 @@ PyObject* PyBSP::get_root(PyBSPObject* self, void* closure)
     return PyBSPNode::create(self->root, (PyObject*)self);
 }
 
+// Property: adjacency (#210)
+PyObject* PyBSP::get_adjacency(PyBSPObject* self, void* closure)
+{
+    if (!self->root) {
+        PyErr_SetString(PyExc_RuntimeError, "BSP not initialized");
+        return nullptr;
+    }
+
+    // Ensure cache is valid
+    ensure_adjacency_cache(self);
+
+    // Create and return adjacency wrapper
+    PyBSPAdjacencyObject* adj = (PyBSPAdjacencyObject*)
+        mcrfpydef::PyBSPAdjacencyType.tp_alloc(&mcrfpydef::PyBSPAdjacencyType, 0);
+    if (!adj) return nullptr;
+
+    adj->bsp_owner = (PyObject*)self;
+    adj->generation = self->generation;
+    Py_INCREF(self);
+
+    return (PyObject*)adj;
+}
+
 // Method: split_once(horizontal, position) -> BSP
 PyObject* PyBSP::split_once(PyBSPObject* self, PyObject* args, PyObject* kwds)
 {
@@ -439,8 +609,10 @@ PyObject* PyBSP::split_once(PyBSPObject* self, PyObject* args, PyObject* kwds)
         return nullptr;
     }
 
-    // Note: split_once only adds children, doesn't remove any nodes
+    // Increment generation to invalidate adjacency cache and stale BSPNode references
-    // Root node pointer remains valid, so we don't increment generation
+    // The tree structure changes, so any cached adjacency graph is now invalid
+    self->generation++;
+
     TCOD_bsp_split_once(self->root, horizontal ? true : false, position);
 
     Py_INCREF(self);
@@ -685,6 +857,40 @@ PyObject* PyBSP::find(PyBSPObject* self, PyObject* args, PyObject* kwds)
     return PyBSPNode::create(found, (PyObject*)self);
 }
 
+// Method: get_leaf(index) -> BSPNode (#210)
+PyObject* PyBSP::get_leaf(PyBSPObject* self, PyObject* args, PyObject* kwds)
+{
+    static const char* keywords[] = {"index", nullptr};
+    int index;
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "i", const_cast<char**>(keywords), &index)) {
+        return nullptr;
+    }
+
+    if (!self->root) {
+        PyErr_SetString(PyExc_RuntimeError, "BSP not initialized");
+        return nullptr;
+    }
+
+    // Ensure adjacency cache is valid (this builds leaf_pointers list)
+    ensure_adjacency_cache(self);
+
+    int n = (int)self->adjacency_cache->leaf_pointers.size();
+
+    // Handle negative indexing
+    if (index < 0) {
+        index += n;
+    }
+
+    if (index < 0 || index >= n) {
+        PyErr_SetString(PyExc_IndexError, "leaf index out of range");
+        return nullptr;
+    }
+
+    TCOD_bsp_t* leaf = self->adjacency_cache->leaf_pointers[index];
+    return PyBSPNode::create(leaf, (PyObject*)self);
+}
+
 // Method: to_heightmap(...) -> HeightMap
 PyObject* PyBSP::to_heightmap(PyBSPObject* self, PyObject* args, PyObject* kwds)
 {
@@ -841,6 +1047,13 @@ PyGetSetDef PyBSPNode::getsetters[] = {
      MCRF_PROPERTY(parent, "Parent node, or None if root. Read-only."), NULL},
     {"sibling", (getter)PyBSPNode::get_sibling, NULL,
      MCRF_PROPERTY(sibling, "Other child of parent, or None. Read-only."), NULL},
+    {"leaf_index", (getter)PyBSPNode::get_leaf_index, NULL,
+     MCRF_PROPERTY(leaf_index, "Leaf index (0..n-1) in adjacency graph, or None if not a leaf. Read-only."), NULL},
+    {"adjacent_tiles", (getter)PyBSPNode::get_adjacent_tiles, NULL,
+     MCRF_PROPERTY(adjacent_tiles, "Mapping of neighbor_index -> tuple of Vector wall tiles. "
+                   "Returns tiles on THIS leaf's boundary suitable for corridor placement. "
+                   "Each Vector has integer coordinates; use .int for (x, y) tuple. "
+                   "Only available for leaf nodes. Read-only."), NULL},
     {NULL}
 };
 
@@ -1080,6 +1293,69 @@ PyObject* PyBSPNode::get_sibling(PyBSPNodeObject* self, void* closure)
     }
 }
 
+// Property: leaf_index (#210)
+PyObject* PyBSPNode::get_leaf_index(PyBSPNodeObject* self, void* closure)
+{
+    if (!checkValid(self)) return nullptr;
+
+    // Only leaves have an index
+    if (!TCOD_bsp_is_leaf(self->node)) {
+        Py_RETURN_NONE;
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+
+    // Ensure cache is valid
+    ensure_adjacency_cache(bsp);
+
+    // Look up this node's index
+    auto it = bsp->adjacency_cache->ptr_to_index.find(self->node);
+    if (it == bsp->adjacency_cache->ptr_to_index.end()) {
+        // Should not happen if node is valid leaf
+        PyErr_SetString(PyExc_RuntimeError, "Leaf node not found in adjacency cache");
+        return nullptr;
+    }
+
+    return PyLong_FromLong(it->second);
+}
+
+// Property: adjacent_tiles (#210)
+PyObject* PyBSPNode::get_adjacent_tiles(PyBSPNodeObject* self, void* closure)
+{
+    if (!checkValid(self)) return nullptr;
+
+    // Only leaves have adjacent_tiles
+    if (!TCOD_bsp_is_leaf(self->node)) {
+        PyErr_SetString(PyExc_ValueError, "adjacent_tiles is only available for leaf nodes");
+        return nullptr;
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+
+    // Ensure cache is valid
+    ensure_adjacency_cache(bsp);
+
+    // Look up this node's index
+    auto it = bsp->adjacency_cache->ptr_to_index.find(self->node);
+    if (it == bsp->adjacency_cache->ptr_to_index.end()) {
+        PyErr_SetString(PyExc_RuntimeError, "Leaf node not found in adjacency cache");
+        return nullptr;
+    }
+
+    // Create adjacent_tiles wrapper
+    PyBSPAdjacentTilesObject* tiles = (PyBSPAdjacentTilesObject*)
+        mcrfpydef::PyBSPAdjacentTilesType.tp_alloc(&mcrfpydef::PyBSPAdjacentTilesType, 0);
+    if (!tiles) return nullptr;
+
+    tiles->bsp_owner = self->bsp_owner;
+    tiles->node = self->node;
+    tiles->leaf_index = it->second;
+    tiles->generation = bsp->generation;
+    Py_INCREF(self->bsp_owner);
+
+    return (PyObject*)tiles;
+}
+
 // Method: contains(pos) -> bool
 PyObject* PyBSPNode::contains(PyBSPNodeObject* self, PyObject* args, PyObject* kwds)
 {
@@ -1167,3 +1443,337 @@ PyObject* PyBSPIter::repr(PyObject* obj)
 
     return PyUnicode_FromString(ss.str().c_str());
 }
+
+// ==================== PyBSPAdjacency Implementation (#210) ====================
+
+// Static method definitions
+PySequenceMethods PyBSPAdjacency::sequence_methods = {
+    .sq_length = (lenfunc)PyBSPAdjacency::len,
+    .sq_item = (ssizeargfunc)PyBSPAdjacency::getitem,
+};
+
+PyMappingMethods PyBSPAdjacency::mapping_methods = {
+    .mp_length = (lenfunc)PyBSPAdjacency::len,
+    .mp_subscript = (binaryfunc)PyBSPAdjacency::subscript,
+};
+
+bool PyBSPAdjacency::checkValid(PyBSPAdjacencyObject* self)
+{
+    if (!self->bsp_owner) {
+        PyErr_SetString(PyExc_RuntimeError, "BSPAdjacency has no parent BSP");
+        return false;
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    if (self->generation != bsp->generation) {
+        PyErr_SetString(PyExc_RuntimeError,
+            "BSPAdjacency is stale: parent BSP was modified. Re-access bsp.adjacency.");
+        return false;
+    }
+
+    return true;
+}
+
+void PyBSPAdjacency::dealloc(PyBSPAdjacencyObject* self)
+{
+    Py_XDECREF(self->bsp_owner);
+    Py_TYPE(self)->tp_free((PyObject*)self);
+}
+
+PyObject* PyBSPAdjacency::repr(PyObject* obj)
+{
+    PyBSPAdjacencyObject* self = (PyBSPAdjacencyObject*)obj;
+
+    if (!self->bsp_owner) {
+        return PyUnicode_FromString("<BSPAdjacency (invalid)>");
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    if (self->generation != bsp->generation) {
+        return PyUnicode_FromString("<BSPAdjacency (stale)>");
+    }
+
+    ensure_adjacency_cache(bsp);
+    int n = (int)bsp->adjacency_cache->leaf_pointers.size();
+
+    std::ostringstream ss;
+    ss << "<BSPAdjacency with " << n << " leaves>";
+    return PyUnicode_FromString(ss.str().c_str());
+}
+
+Py_ssize_t PyBSPAdjacency::len(PyBSPAdjacencyObject* self)
+{
+    if (!checkValid(self)) return -1;
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    return (Py_ssize_t)bsp->adjacency_cache->leaf_pointers.size();
+}
+
+PyObject* PyBSPAdjacency::getitem(PyBSPAdjacencyObject* self, Py_ssize_t index)
+{
+    if (!checkValid(self)) return nullptr;
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    int n = (int)bsp->adjacency_cache->leaf_pointers.size();
+
+    // Handle negative indexing
+    if (index < 0) {
+        index += n;
+    }
+
+    if (index < 0 || index >= n) {
+        PyErr_SetString(PyExc_IndexError, "leaf index out of range");
+        return nullptr;
+    }
+
+    // Get neighbors for this leaf
+    const auto& neighbors = bsp->adjacency_cache->graph[index];
+
+    // Build tuple of neighbor indices
+    PyObject* result = PyTuple_New(neighbors.size());
+    if (!result) return nullptr;
+
+    for (size_t i = 0; i < neighbors.size(); i++) {
+        PyTuple_SET_ITEM(result, i, PyLong_FromLong(neighbors[i]));
+    }
+
+    return result;
+}
+
+PyObject* PyBSPAdjacency::subscript(PyBSPAdjacencyObject* self, PyObject* key)
+{
+    if (!PyLong_Check(key)) {
+        PyErr_SetString(PyExc_TypeError, "adjacency indices must be integers");
+        return nullptr;
+    }
+
+    Py_ssize_t index = PyLong_AsSsize_t(key);
+    if (index == -1 && PyErr_Occurred()) return nullptr;
+
+    return getitem(self, index);
+}
+
+PyObject* PyBSPAdjacency::iter(PyBSPAdjacencyObject* self)
+{
+    if (!checkValid(self)) return nullptr;
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    // Create a list of tuples for iteration
+    int n = (int)bsp->adjacency_cache->leaf_pointers.size();
+    PyObject* list = PyList_New(n);
+    if (!list) return nullptr;
+
+    for (int i = 0; i < n; i++) {
+        const auto& neighbors = bsp->adjacency_cache->graph[i];
+        PyObject* tuple = PyTuple_New(neighbors.size());
+        if (!tuple) {
+            Py_DECREF(list);
+            return nullptr;
+        }
+        for (size_t j = 0; j < neighbors.size(); j++) {
+            PyTuple_SET_ITEM(tuple, j, PyLong_FromLong(neighbors[j]));
+        }
+        PyList_SET_ITEM(list, i, tuple);
+    }
+
+    // Return iterator over the list
+    PyObject* iter = PyObject_GetIter(list);
+    Py_DECREF(list);
+    return iter;
+}
+
+// ==================== PyBSPAdjacentTiles Implementation (#210) ====================
+
+// Static method definitions
+PyMappingMethods PyBSPAdjacentTiles::mapping_methods = {
+    .mp_length = (lenfunc)PyBSPAdjacentTiles::len,
+    .mp_subscript = (binaryfunc)PyBSPAdjacentTiles::subscript,
+};
+
+// Sequence methods for 'in' operator support
+PySequenceMethods PyBSPAdjacentTiles::sequence_methods = {
+    .sq_length = (lenfunc)PyBSPAdjacentTiles::len,
+    .sq_contains = (objobjproc)PyBSPAdjacentTiles::contains,
+};
+
+PyMethodDef PyBSPAdjacentTiles::methods[] = {
+    {"keys", (PyCFunction)PyBSPAdjacentTiles::keys, METH_NOARGS,
+     "Return tuple of adjacent neighbor indices."},
+    {NULL}
+};
+
+bool PyBSPAdjacentTiles::checkValid(PyBSPAdjacentTilesObject* self)
+{
+    if (!self->bsp_owner) {
+        PyErr_SetString(PyExc_RuntimeError, "BSPAdjacentTiles has no parent BSP");
+        return false;
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    if (self->generation != bsp->generation) {
+        PyErr_SetString(PyExc_RuntimeError,
+            "BSPAdjacentTiles is stale: parent BSP was modified. Re-access node.adjacent_tiles.");
+        return false;
+    }
+
+    return true;
+}
+
+void PyBSPAdjacentTiles::dealloc(PyBSPAdjacentTilesObject* self)
+{
+    Py_XDECREF(self->bsp_owner);
+    Py_TYPE(self)->tp_free((PyObject*)self);
+}
+
+PyObject* PyBSPAdjacentTiles::repr(PyObject* obj)
+{
+    PyBSPAdjacentTilesObject* self = (PyBSPAdjacentTilesObject*)obj;
+
+    if (!self->bsp_owner) {
+        return PyUnicode_FromString("<BSPAdjacentTiles (invalid)>");
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    if (self->generation != bsp->generation) {
+        return PyUnicode_FromString("<BSPAdjacentTiles (stale)>");
+    }
+
+    ensure_adjacency_cache(bsp);
+    const auto& neighbors = bsp->adjacency_cache->graph[self->leaf_index];
+
+    std::ostringstream ss;
+    ss << "<BSPAdjacentTiles for leaf " << self->leaf_index
+       << " with " << neighbors.size() << " neighbors>";
+    return PyUnicode_FromString(ss.str().c_str());
+}
+
+Py_ssize_t PyBSPAdjacentTiles::len(PyBSPAdjacentTilesObject* self)
+{
+    if (!checkValid(self)) return -1;
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    return (Py_ssize_t)bsp->adjacency_cache->graph[self->leaf_index].size();
+}
+
+PyObject* PyBSPAdjacentTiles::subscript(PyBSPAdjacentTilesObject* self, PyObject* key)
+{
+    if (!checkValid(self)) return nullptr;
+
+    if (!PyLong_Check(key)) {
+        PyErr_SetString(PyExc_TypeError, "adjacent_tiles keys must be integers (neighbor leaf index)");
+        return nullptr;
+    }
+
+    int neighbor_index = (int)PyLong_AsLong(key);
+    if (neighbor_index == -1 && PyErr_Occurred()) return nullptr;
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    // Validate neighbor_index is in range
+    int n = (int)bsp->adjacency_cache->leaf_pointers.size();
+    if (neighbor_index < 0 || neighbor_index >= n) {
+        PyErr_Format(PyExc_KeyError, "%d", neighbor_index);
+        return nullptr;
+    }
+
+    // Check if neighbor_index is actually a neighbor
+    const auto& neighbors = bsp->adjacency_cache->graph[self->leaf_index];
+    bool is_neighbor = false;
+    for (int ni : neighbors) {
+        if (ni == neighbor_index) {
+            is_neighbor = true;
+            break;
+        }
+    }
+
+    if (!is_neighbor) {
+        PyErr_Format(PyExc_KeyError, "%d (not adjacent to leaf %d)", neighbor_index, self->leaf_index);
+        return nullptr;
+    }
+
+    // Get or compute wall tiles
+    // Key is (self, neighbor) - NOT symmetric! Each direction has different tiles.
+    auto& cache = *bsp->adjacency_cache;
+    auto cache_key = std::make_pair(self->leaf_index, neighbor_index);
+
+    auto it = cache.wall_tiles_cache.find(cache_key);
+    if (it == cache.wall_tiles_cache.end()) {
+        // Compute and cache - returns tiles on self's edge bordering neighbor
+        TCOD_bsp_t* this_node = cache.leaf_pointers[self->leaf_index];
+        TCOD_bsp_t* other_node = cache.leaf_pointers[neighbor_index];
+        cache.wall_tiles_cache[cache_key] = compute_wall_tiles(this_node, other_node);
+        it = cache.wall_tiles_cache.find(cache_key);
+    }
+
+    // Build tuple of Vector objects
+    const auto& tiles = it->second;
+    PyObject* result = PyTuple_New(tiles.size());
+    if (!result) return nullptr;
+
+    for (size_t i = 0; i < tiles.size(); i++) {
+        // Convert sf::Vector2i to Python Vector (sf::Vector2f)
+        PyVector vec(sf::Vector2f((float)tiles[i].x, (float)tiles[i].y));
+        PyObject* py_vec = vec.pyObject();
+        if (!py_vec) {
+            Py_DECREF(result);
+            return nullptr;
+        }
+        PyTuple_SET_ITEM(result, i, py_vec);
+    }
+
+    return result;
+}
+
+int PyBSPAdjacentTiles::contains(PyBSPAdjacentTilesObject* self, PyObject* key)
+{
+    if (!checkValid(self)) return -1;
+
+    if (!PyLong_Check(key)) {
+        return 0;  // Non-integer keys are not contained
+    }
+
+    int neighbor_index = (int)PyLong_AsLong(key);
+    if (neighbor_index == -1 && PyErr_Occurred()) {
+        PyErr_Clear();
+        return 0;
+    }
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    const auto& neighbors = bsp->adjacency_cache->graph[self->leaf_index];
+    for (int ni : neighbors) {
+        if (ni == neighbor_index) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+PyObject* PyBSPAdjacentTiles::keys(PyBSPAdjacentTilesObject* self, PyObject* Py_UNUSED(args))
+{
+    if (!checkValid(self)) return nullptr;
+
+    PyBSPObject* bsp = (PyBSPObject*)self->bsp_owner;
+    ensure_adjacency_cache(bsp);
+
+    const auto& neighbors = bsp->adjacency_cache->graph[self->leaf_index];
+
+    PyObject* result = PyTuple_New(neighbors.size());
+    if (!result) return nullptr;
+
+    for (size_t i = 0; i < neighbors.size(); i++) {
+        PyTuple_SET_ITEM(result, i, PyLong_FromLong(neighbors[i]));
+    }
+
+    return result;
+}

src/PyBSP.h

@@ -4,10 +4,26 @@
 #include <libtcod.h>
 #include <vector>
 #include <cstdint>
+#include <unordered_map>
+#include <map>
+#include <SFML/System/Vector2.hpp>
 
 // Forward declarations
 class PyBSP;
 class PyBSPNode;
+class PyBSPAdjacency;
+class PyBSPAdjacentTiles;
+
+// Adjacency cache - computed lazily, invalidated on generation change (#210)
+struct BSPAdjacencyCache {
+    std::vector<std::vector<int>> graph;              // graph[i] = neighbor indices for leaf i
+    std::vector<TCOD_bsp_t*> leaf_pointers;           // leaf_pointers[i] = TCOD node for leaf i
+    std::unordered_map<TCOD_bsp_t*, int> ptr_to_index; // Reverse lookup: node ptr -> index
+    uint64_t generation;                               // Generation when computed
+    // Wall tile cache: key=(self_index, neighbor_index) - perspective matters!
+    // leaf0.adjacent_tiles[1] returns tiles on leaf0's edge, not symmetric with leaf1.adjacent_tiles[0]
+    std::map<std::pair<int,int>, std::vector<sf::Vector2i>> wall_tiles_cache;
+};
 
 // Maximum recursion depth to prevent memory exhaustion
 // 2^16 = 65536 potential leaf nodes, which is already excessive
@@ -20,6 +36,7 @@ typedef struct {
     int orig_x, orig_y;         // Original bounds for clear()
     int orig_w, orig_h;
     uint64_t generation;        // Incremented on structural changes (clear, split)
+    BSPAdjacencyCache* adjacency_cache;  // Lazy-computed adjacency graph (#210)
 } PyBSPObject;
 
 // Python object structure for BSPNode (lightweight reference)
@@ -39,6 +56,22 @@ typedef struct {
     uint64_t generation;              // Generation at iterator creation
 } PyBSPIterObject;
 
+// Python object for BSP.adjacency property (#210)
+typedef struct {
+    PyObject_HEAD
+    PyObject* bsp_owner;        // Reference to PyBSPObject
+    uint64_t generation;        // Generation at creation (for validity check)
+} PyBSPAdjacencyObject;
+
+// Python object for BSPNode.adjacent_tiles property (#210)
+typedef struct {
+    PyObject_HEAD
+    PyObject* bsp_owner;        // Reference to PyBSPObject
+    TCOD_bsp_t* node;           // The leaf node this belongs to
+    int leaf_index;             // This leaf's index in adjacency graph
+    uint64_t generation;        // Generation at creation (for validity check)
+} PyBSPAdjacentTilesObject;
+
 class PyBSP
 {
 public:
@@ -53,6 +86,7 @@ public:
     static PyObject* get_pos(PyBSPObject* self, void* closure);
     static PyObject* get_size(PyBSPObject* self, void* closure);
     static PyObject* get_root(PyBSPObject* self, void* closure);
+    static PyObject* get_adjacency(PyBSPObject* self, void* closure);  // #210
 
     // Splitting methods (#202)
     static PyObject* split_once(PyBSPObject* self, PyObject* args, PyObject* kwds);
@@ -65,6 +99,7 @@ public:
 
     // Query methods (#205)
     static PyObject* find(PyBSPObject* self, PyObject* args, PyObject* kwds);
+    static PyObject* get_leaf(PyBSPObject* self, PyObject* args, PyObject* kwds);  // #210
 
     // HeightMap conversion (#206)
     static PyObject* to_heightmap(PyBSPObject* self, PyObject* args, PyObject* kwds);
@@ -106,6 +141,10 @@ public:
     static PyObject* get_parent(PyBSPNodeObject* self, void* closure);
     static PyObject* get_sibling(PyBSPNodeObject* self, void* closure);
 
+    // Adjacency properties (#210)
+    static PyObject* get_leaf_index(PyBSPNodeObject* self, void* closure);
+    static PyObject* get_adjacent_tiles(PyBSPNodeObject* self, void* closure);
+
     // Methods (#203)
     static PyObject* contains(PyBSPNodeObject* self, PyObject* args, PyObject* kwds);
     static PyObject* center(PyBSPNodeObject* self, PyObject* Py_UNUSED(args));
@@ -132,6 +171,39 @@ public:
     static PyObject* repr(PyObject* obj);
 };
 
+// BSP Adjacency wrapper class (#210)
+class PyBSPAdjacency
+{
+public:
+    static void dealloc(PyBSPAdjacencyObject* self);
+    static PyObject* repr(PyObject* obj);
+    static Py_ssize_t len(PyBSPAdjacencyObject* self);
+    static PyObject* getitem(PyBSPAdjacencyObject* self, Py_ssize_t index);
+    static PyObject* subscript(PyBSPAdjacencyObject* self, PyObject* key);
+    static PyObject* iter(PyBSPAdjacencyObject* self);
+    static bool checkValid(PyBSPAdjacencyObject* self);
+
+    static PySequenceMethods sequence_methods;
+    static PyMappingMethods mapping_methods;
+};
+
+// BSP Adjacent Tiles wrapper class (#210)
+class PyBSPAdjacentTiles
+{
+public:
+    static void dealloc(PyBSPAdjacentTilesObject* self);
+    static PyObject* repr(PyObject* obj);
+    static Py_ssize_t len(PyBSPAdjacentTilesObject* self);
+    static PyObject* subscript(PyBSPAdjacentTilesObject* self, PyObject* key);
+    static int contains(PyBSPAdjacentTilesObject* self, PyObject* key);
+    static PyObject* keys(PyBSPAdjacentTilesObject* self, PyObject* Py_UNUSED(args));
+    static bool checkValid(PyBSPAdjacentTilesObject* self);
+
+    static PyMappingMethods mapping_methods;
+    static PySequenceMethods sequence_methods;  // For 'in' operator
+    static PyMethodDef methods[];
+};
+
 // Traversal enum creation
 class PyTraversal
 {
@@ -237,4 +309,53 @@ namespace mcrfpydef {
             return NULL;
         },
     };
+
+    // BSP Adjacency - internal type for BSP.adjacency property (#210)
+    inline PyTypeObject PyBSPAdjacencyType = {
+        .ob_base = {.ob_base = {.ob_refcnt = 1, .ob_type = NULL}, .ob_size = 0},
+        .tp_name = "mcrfpy.BSPAdjacency",
+        .tp_basicsize = sizeof(PyBSPAdjacencyObject),
+        .tp_itemsize = 0,
+        .tp_dealloc = (destructor)PyBSPAdjacency::dealloc,
+        .tp_repr = PyBSPAdjacency::repr,
+        .tp_as_sequence = &PyBSPAdjacency::sequence_methods,
+        .tp_as_mapping = &PyBSPAdjacency::mapping_methods,
+        .tp_flags = Py_TPFLAGS_DEFAULT,
+        .tp_doc = PyDoc_STR(
+            "BSPAdjacency - Sequence of leaf neighbor tuples.\n\n"
+            "Accessed via BSP.adjacency property. adjacency[i] returns a tuple\n"
+            "of leaf indices that are adjacent to (share a wall with) leaf i.\n"
+        ),
+        .tp_iter = (getiterfunc)PyBSPAdjacency::iter,
+        .tp_new = [](PyTypeObject* type, PyObject* args, PyObject* kwds) -> PyObject* {
+            PyErr_SetString(PyExc_TypeError, "BSPAdjacency cannot be instantiated directly");
+            return NULL;
+        },
+    };
+
+    // BSP Adjacent Tiles - internal type for BSPNode.adjacent_tiles property (#210)
+    inline PyTypeObject PyBSPAdjacentTilesType = {
+        .ob_base = {.ob_base = {.ob_refcnt = 1, .ob_type = NULL}, .ob_size = 0},
+        .tp_name = "mcrfpy.BSPAdjacentTiles",
+        .tp_basicsize = sizeof(PyBSPAdjacentTilesObject),
+        .tp_itemsize = 0,
+        .tp_dealloc = (destructor)PyBSPAdjacentTiles::dealloc,
+        .tp_repr = PyBSPAdjacentTiles::repr,
+        .tp_as_sequence = &PyBSPAdjacentTiles::sequence_methods,  // For 'in' operator
+        .tp_as_mapping = &PyBSPAdjacentTiles::mapping_methods,
+        .tp_flags = Py_TPFLAGS_DEFAULT,
+        .tp_doc = PyDoc_STR(
+            "BSPAdjacentTiles - Mapping of neighbor index to wall tile coordinates.\n\n"
+            "Accessed via BSPNode.adjacent_tiles property. adjacent_tiles[j] returns\n"
+            "a tuple of Vector coordinates representing tiles on THIS leaf's edge that\n"
+            "border neighbor j. Each Vector has integer x/y coordinates (use .int for tuple).\n"
+            "Raises KeyError if j is not an adjacent leaf.\n\n"
+            "Supports 'in' operator: `5 in leaf.adjacent_tiles` checks if leaf 5 is adjacent.\n"
+        ),
+        .tp_methods = PyBSPAdjacentTiles::methods,
+        .tp_new = [](PyTypeObject* type, PyObject* args, PyObject* kwds) -> PyObject* {
+            PyErr_SetString(PyExc_TypeError, "BSPAdjacentTiles cannot be instantiated directly");
+            return NULL;
+        },
+    };
 }

tests/unit/bsp_adjacency_test.py

@@ -0,0 +1,323 @@
+#!/usr/bin/env python3
+"""Tests for BSP adjacency graph feature (#210)"""
+
+import mcrfpy
+import sys
+
+def test_adjacency_basic():
+    """Test basic adjacency on a simple 2-leaf BSP"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 50))
+    # Split once - creates 2 leaves
+    bsp.split_once(horizontal=False, position=50)  # Vertical split at x=50
+
+    leaves = list(bsp.leaves())
+    assert len(leaves) == 2, f"Expected 2 leaves, got {len(leaves)}"
+
+    # Access adjacency
+    adj = bsp.adjacency
+    assert len(adj) == 2, f"Expected adjacency len 2, got {len(adj)}"
+
+    # Each leaf should be adjacent to the other
+    neighbors_0 = adj[0]
+    neighbors_1 = adj[1]
+
+    assert 1 in neighbors_0, f"Leaf 0 should be adjacent to leaf 1, got {neighbors_0}"
+    assert 0 in neighbors_1, f"Leaf 1 should be adjacent to leaf 0, got {neighbors_1}"
+
+    print("  test_adjacency_basic: PASS")
+
+def test_leaf_indexing():
+    """Test that leaf_index property works correctly"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=2, min_size=(10, 10), seed=42)
+
+    leaves = list(bsp.leaves())
+
+    # Each leaf should have a valid index
+    for i, leaf in enumerate(leaves):
+        assert leaf.leaf_index == i, f"Leaf {i} has index {leaf.leaf_index}"
+
+    # Non-leaves should return None
+    root = bsp.root
+    if not root.is_leaf:
+        assert root.leaf_index is None, "Non-leaf should have leaf_index=None"
+
+    print("  test_leaf_indexing: PASS")
+
+def test_adjacency_symmetry():
+    """Test that adjacency is symmetric: if A adjacent to B, then B adjacent to A"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=3, min_size=(10, 10), seed=42)
+
+    adj = bsp.adjacency
+    n = len(adj)
+
+    for i in range(n):
+        for j in adj[i]:
+            assert i in adj[j], f"Adjacency not symmetric: {i} -> {j} but not {j} -> {i}"
+
+    print("  test_adjacency_symmetry: PASS")
+
+def test_adjacent_tiles_basic():
+    """Test that adjacent_tiles returns Vector tuples"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 50))
+    bsp.split_once(horizontal=False, position=50)  # Vertical split at x=50
+
+    leaves = list(bsp.leaves())
+    assert len(leaves) == 2
+
+    leaf0 = leaves[0]
+    neighbors = bsp.adjacency[0]
+    assert len(neighbors) > 0, "Leaf 0 should have neighbors"
+
+    neighbor_idx = neighbors[0]
+    wall_tiles = leaf0.adjacent_tiles[neighbor_idx]
+
+    assert len(wall_tiles) > 0, "Should have wall tiles"
+
+    # Check that wall tiles are Vector objects
+    first_tile = wall_tiles[0]
+    assert hasattr(first_tile, 'x') and hasattr(first_tile, 'y'), \
+        f"Wall tile should be a Vector, got {type(first_tile)}"
+
+    print("  test_adjacent_tiles_basic: PASS")
+
+def test_adjacent_tiles_keyerror():
+    """Test that non-adjacent lookups raise KeyError"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=3, min_size=(10, 10), seed=42)
+
+    leaves = list(bsp.leaves())
+
+    # Find a non-adjacent pair
+    adj = bsp.adjacency
+    for i in range(len(leaves)):
+        for j in range(len(leaves)):
+            if i != j and j not in adj[i]:
+                # i and j are not adjacent
+                try:
+                    _ = leaves[i].adjacent_tiles[j]
+                    assert False, f"Expected KeyError for non-adjacent pair {i}, {j}"
+                except KeyError:
+                    pass  # Expected
+                print("  test_adjacent_tiles_keyerror: PASS")
+                return
+
+    # If we get here, all pairs are adjacent (unlikely with depth 3)
+    print("  test_adjacent_tiles_keyerror: SKIP (all pairs adjacent)")
+
+def test_cache_invalidation():
+    """Test that cache is invalidated on clear() and split_recursive()"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=2, min_size=(10, 10), seed=42)
+
+    # Access adjacency to populate cache
+    adj1 = bsp.adjacency
+    n1 = len(adj1)
+
+    # Clear and re-split
+    bsp.clear()
+    bsp.split_recursive(depth=3, min_size=(10, 10), seed=123)
+
+    # Access adjacency again - should be rebuilt
+    adj2 = bsp.adjacency
+    n2 = len(adj2)
+
+    # Different seed/depth should give different results
+    assert n2 > n1 or n2 != n1, "Cache should be invalidated after clear()"
+
+    print("  test_cache_invalidation: PASS")
+
+def test_wall_tiles_on_boundary():
+    """Test that wall tiles are on the correct boundary"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 50))
+    bsp.split_once(horizontal=False, position=50)  # Vertical split at x=50
+
+    leaves = list(bsp.leaves())
+    leaf0 = leaves[0]  # Should be left side (x: 0-50)
+    leaf1 = leaves[1]  # Should be right side (x: 50-100)
+
+    # Get wall tiles from leaf0 to leaf1
+    wall_tiles = leaf0.adjacent_tiles[1]
+
+    # Wall should be at x=49 (last column of leaf0) for leaf0
+    for tile in wall_tiles:
+        x, y = int(tile.x), int(tile.y)
+        # Tile should be within leaf0's bounds
+        assert x == 49, f"Wall tile x should be 49 (boundary), got {x}"
+        assert 0 <= y < 50, f"Wall tile y should be in range 0-49, got {y}"
+
+    print("  test_wall_tiles_on_boundary: PASS")
+
+def test_negative_indexing():
+    """Test that negative indices work for adjacency"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=2, min_size=(10, 10), seed=42)
+
+    adj = bsp.adjacency
+    n = len(adj)
+
+    # adj[-1] should be same as adj[n-1]
+    last_positive = adj[n-1]
+    last_negative = adj[-1]
+
+    assert last_positive == last_negative, \
+        f"Negative indexing failed: adj[-1]={last_negative}, adj[{n-1}]={last_positive}"
+
+    print("  test_negative_indexing: PASS")
+
+def test_iteration():
+    """Test that adjacency can be iterated"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=2, min_size=(10, 10), seed=42)
+
+    adj = bsp.adjacency
+
+    # Should be iterable
+    count = 0
+    for neighbors in adj:
+        assert isinstance(neighbors, tuple), f"Expected tuple, got {type(neighbors)}"
+        count += 1
+
+    assert count == len(adj), f"Iteration count {count} != len {len(adj)}"
+
+    print("  test_iteration: PASS")
+
+def test_keys_method():
+    """Test that adjacent_tiles.keys() works"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 50))
+    bsp.split_once(horizontal=False, position=50)
+
+    leaves = list(bsp.leaves())
+    leaf0 = leaves[0]
+
+    keys = leaf0.adjacent_tiles.keys()
+    assert isinstance(keys, tuple), f"keys() should return tuple, got {type(keys)}"
+    assert len(keys) > 0, "Should have at least one neighbor"
+    assert 1 in keys, f"Leaf 1 should be in keys, got {keys}"
+
+    print("  test_keys_method: PASS")
+
+def test_split_once_invalidation():
+    """Test that split_once invalidates adjacency cache and BSPNode references"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+
+    # First split - creates 2 leaves
+    bsp.split_once(horizontal=False, position=50)
+
+    # Access adjacency to build cache
+    adj1 = bsp.adjacency
+    n1 = len(adj1)
+    assert n1 == 2, f"Expected 2 leaves after first split, got {n1}"
+
+    # Get a reference to a leaf before second split
+    old_leaf = list(bsp.leaves())[0]
+    old_leaf_index = old_leaf.leaf_index
+
+    # Second split_once on the BSP (note: split_once always works on root)
+    # After this, the tree structure changes, but old_leaf should be stale
+    bsp.clear()  # Clear and split fresh to get more leaves
+    bsp.split_once(horizontal=False, position=50)
+    bsp.split_once(horizontal=True, position=50)  # Won't work - split_once only on root
+
+    # The old leaf reference should now be stale
+    try:
+        _ = old_leaf.leaf_index
+        assert False, "Expected RuntimeError for stale BSPNode"
+    except RuntimeError:
+        pass  # Expected - node is stale after clear()
+
+    # Access adjacency - should reflect new structure (2 leaves again)
+    adj2 = bsp.adjacency
+    n2 = len(adj2)
+    assert n2 == 2, f"Expected 2 leaves after clear+split, got {n2}"
+
+    print("  test_split_once_invalidation: PASS")
+
+def test_wall_tiles_perspective():
+    """Test that wall tiles are from the correct leaf's perspective"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 50))
+    bsp.split_once(horizontal=False, position=50)  # Vertical split at x=50
+
+    leaves = list(bsp.leaves())
+    leaf0 = leaves[0]  # Left side: x 0-50
+    leaf1 = leaves[1]  # Right side: x 50-100
+
+    # Get tiles from leaf0's perspective (should be at x=49, leaf0's edge)
+    tiles_0_to_1 = leaf0.adjacent_tiles[1]
+    for tile in tiles_0_to_1:
+        assert int(tile.x) == 49, f"Leaf0->Leaf1 tile should be at x=49, got {tile.x}"
+
+    # Get tiles from leaf1's perspective (should be at x=50, leaf1's edge)
+    tiles_1_to_0 = leaf1.adjacent_tiles[0]
+    for tile in tiles_1_to_0:
+        assert int(tile.x) == 50, f"Leaf1->Leaf0 tile should be at x=50, got {tile.x}"
+
+    print("  test_wall_tiles_perspective: PASS")
+
+def test_get_leaf():
+    """Test bsp.get_leaf(index) method"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 100))
+    bsp.split_recursive(depth=2, min_size=(10, 10), seed=42)
+
+    leaves = list(bsp.leaves())
+    n = len(leaves)
+
+    # Test positive indices
+    for i in range(n):
+        leaf = bsp.get_leaf(i)
+        assert leaf.leaf_index == i, f"get_leaf({i}) returned leaf with index {leaf.leaf_index}"
+
+    # Test negative index
+    last_leaf = bsp.get_leaf(-1)
+    assert last_leaf.leaf_index == n - 1, f"get_leaf(-1) should return leaf {n-1}, got {last_leaf.leaf_index}"
+
+    # Test out of range
+    try:
+        bsp.get_leaf(n)
+        assert False, "Expected IndexError for out-of-range index"
+    except IndexError:
+        pass  # Expected
+
+    print("  test_get_leaf: PASS")
+
+def test_contains_operator():
+    """Test 'in' operator for adjacent_tiles"""
+    bsp = mcrfpy.BSP(pos=(0, 0), size=(100, 50))
+    bsp.split_once(horizontal=False, position=50)
+
+    leaves = list(bsp.leaves())
+    leaf0 = leaves[0]
+
+    # Leaf 1 should be adjacent to leaf 0
+    assert 1 in leaf0.adjacent_tiles, "1 should be in leaf0.adjacent_tiles"
+
+    # Some arbitrary index should not be (assuming only 2 leaves)
+    assert 5 not in leaf0.adjacent_tiles, "5 should not be in leaf0.adjacent_tiles"
+
+    print("  test_contains_operator: PASS")
+
+def run_all_tests():
+    """Run all adjacency tests"""
+    print("Running BSP adjacency tests (#210)...")
+
+    test_adjacency_basic()
+    test_leaf_indexing()
+    test_adjacency_symmetry()
+    test_adjacent_tiles_basic()
+    test_adjacent_tiles_keyerror()
+    test_cache_invalidation()
+    test_wall_tiles_on_boundary()
+    test_negative_indexing()
+    test_iteration()
+    test_keys_method()
+    test_split_once_invalidation()
+    test_wall_tiles_perspective()
+    test_get_leaf()
+    test_contains_operator()
+
+    print("\nAll BSP adjacency tests passed!")
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(run_all_tests())