wip(L26, side branch): every passage style walkable in both recipes (0/0/0); SW bridges look wrong

All 4 styles x both recipes pass capsule, open-air and naturalness audits, and full-view hashes are
deterministic. But the SW passage crosses 355 m of open SurfaceWorld sky as a ~2 km fragmented rock
ramp, which is not natural. L27 replaces long bridges with a shared ceiling-to-ground rock column.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/BuildLinux.sh

@@ -36,8 +36,9 @@ command -v ar >/dev/null || { printf 'ar not found\n' >&2; exit 2; }
 command -v pkg-config >/dev/null || { printf 'pkg-config not found\n' >&2; exit 2; }
 pkg-config --exists egl glesv2 libpng || { printf 'EGL, GLESv2, and libpng development files are required\n' >&2; exit 2; }
 
-BUILD_DIR="$ROOT/Build/linux-$VARIANT"
-BIN_DIR="$ROOT/bin/linux"
+BUILD_ROOT="${VOXELFORGE_BUILD_ROOT:-$ROOT/Build}"
+BIN_DIR="${VOXELFORGE_BIN_DIR:-$ROOT/bin/linux}"
+BUILD_DIR="$BUILD_ROOT/linux-$VARIANT"
 mkdir -p "$BUILD_DIR/wrappers" "$BUILD_DIR/objects" "$BIN_DIR"
 
 INCLUDES=(