feat(nav): 17.1/17.3 - ludic.nav over Recast & Detour v1.6.0 (zlib), built here from the pinned tag on the Mac and the PC (the DLL imports KERNEL32 alone): a navmesh per kind of walker from triangles with an area byte each and cylinders nothing stands in, saved and loaded as bytes; the nearest point, a path as corners (partial when the end cannot be reached), whether a straight line stays walkable, a cost per kind of ground. Tests on a hand-built meadow: round a post, over a ford, stopped at a bank, a saved mesh answering alike - Mac and PC

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.nav/native/shim/nav_shim.cpp

@@ -0,0 +1,50 @@
+// nav_shim.cpp - ludic.nav's door into Recast & Detour (phase 17). The shim rules of
+// packages/README.md: int, float and opaque handles cross; no struct by value, no callback into
+// Ludic; what a query finds is written into a buffer the package owns; errors are return codes.
+#include <Recast.h>
+#include <DetourNavMesh.h>
+#include <DetourNavMeshBuilder.h>
+#include <DetourNavMeshQuery.h>
+#include <DetourCommon.h>
+#include <cstring>
+#include <cmath>
+#include <vector>
+
+#if defined(_WIN32)
+#define NAV_SHIM extern "C" __declspec(dllexport)
+#else
+#define NAV_SHIM extern "C" __attribute__((visibility("default")))
+#endif
+
+namespace {
+const int NAV_MAX_POLYS = 512;     // polygons a path may cross; a longer one is cut there
+const int NAV_MAX_NODES = 4096;    // the search's open list
+
+// a navmesh and the one query that walks it, with the scratch a path needs
+struct Nav {
+  dtNavMesh *mesh = nullptr;
+  dtNavMeshQuery *query = nullptr;
+  dtQueryFilter filter;
+  float ext[3] = {2.0f, 4.0f, 2.0f};   // how far to look for the mesh around a point
+  dtPolyRef polys[NAV_MAX_POLYS];
+  unsigned char *data = nullptr;       // the tile as built or loaded (the mesh frees it)
+  int size = 0;
+  int partial = 0;                     // the last path stopped short of its end
+};
+
+Nav *nav_from(unsigned char *data, int size) {
+  Nav *n = new Nav();
+  n->mesh = dtAllocNavMesh();
+  if (!n->mesh || dtStatusFailed(n->mesh->init(data, size, DT_TILE_FREE_DATA))) { dtFree(data); dtFreeNavMesh(n->mesh); delete n; return nullptr; }
+  n->data = data;
+  n->size = size;
+  n->query = dtAllocNavMeshQuery();
+  if (!n->query || dtStatusFailed(n->query->init(n->mesh, NAV_MAX_NODES))) { dtFreeNavMeshQuery(n->query); dtFreeNavMesh(n->mesh); delete n; return nullptr; }
+  n->filter.setIncludeFlags(0xffff);
+  n->filter.setExcludeFlags(0);
+  return n;
+}
+}  // namespace
+
+#include "nav_build.inl"
+#include "nav_query.inl"