1 files changed, 46 insertions, 0 deletions
diff --git a/internal/validate/grid_test.go b/internal/validate/grid_test.go
index 9a8ef02..b3f834a 100644
--- a/internal/validate/grid_test.go
+++ b/internal/validate/grid_test.go
@@ -103,3 +103,49 @@ func TestGridMultiPlaneViaUpDown(t *testing.T) {
 		t.Errorf("expected an overlap in plane origin 10, got: %+v", issues)
 	}
 }
+
+func TestGridDiagonalClean(t *testing.T) {
+	// Room 1 -> NE -> Room 2 (at 1,-1). Clean diagonal placement.
+	rooms := map[int]string{
+		1: "exits:\n  northeast: 2\n",
+		2: "name: two\n  exits:\n  southwest: 1\n",
+	}
+	if issues := runGridCheck(t, rooms, 1); len(issues) != 0 {
+		t.Errorf("expected no grid issues, got: %+v", issues)
+	}
+}
+
+func TestGridDiagonalOverlap(t *testing.T) {
+	// Two different rooms both resolve to (2,1):
+	// 1→SE→2→E→4 lands 4 at (2,1).
+	// 1→E→3→SE→5 lands 5 at (2,1). Room 4 != 5 → overlap.
+	rooms := map[int]string{
+		1: "exits:\n  southeast: 2\n  east: 3\n",
+		2: "exits:\n  east: 4\n",
+		3: "exits:\n  southeast: 5\n",
+		4: "name: four\n",
+		5: "name: five\n",
+	}
+	issues := runGridCheck(t, rooms, 1)
+	if !containsMsg(issues, "Grid overlap") {
+		t.Errorf("expected a grid overlap via diagonal, got: %+v", issues)
+	}
+}
+
+func TestGridDiagonalTwist(t *testing.T) {
+	// Room 4 forced onto two different cells:
+	// path1: 1→E→2 (2 at 1,0). 2→NE→4 places 4 at (2,-1).
+	// path2: 1→N→3 (3 at 0,-1). 3→E→5 (5 at 1,-1). 5→N→4 wants 4 at (1,-2).
+	// 4 already placed at (2,-1) but wanted at (1,-2) → twist.
+	rooms := map[int]string{
+		1: "exits:\n  east: 2\n  north: 3\n",
+		2: "exits:\n  northeast: 4\n",
+		3: "exits:\n  east: 5\n",
+		4: "name: four\n",
+		5: "exits:\n  north: 4\n",
+	}
+	issues := runGridCheck(t, rooms, 1)
+	if !containsMsg(issues, "Grid twist") {
+		t.Errorf("expected a grid twist via diagonal, got: %+v", issues)
+	}
+}