Fix pattern border normalization

tests/test_core.py

@@ -135,3 +135,31 @@ class CoreTests(unittest.TestCase):
         )
         self.assertIn("|..|##|", normalized)
         self.assertIn("|##|..|", normalized)
+
+    def test_pattern_normalization_keeps_top_and_bottom_borders(self) -> None:
+        board = "\n".join(
+            [
+                "              1    ",
+                "     1  2  3  3  3 ",
+                "   +--+--+--+--+--+",
+                "2 1|  |  |  |  |  |",
+                "   +--+--+--+--+--+",
+                "  1|  |  |  |  |  |",
+                "   +--+--+--+--+--+",
+                "  3|  |  |  |  |  |",
+                "   +--+--+--+--+--+",
+                "  3|  |  |  |  |  |",
+                "   +--+--+--+--+--+",
+                "  3|  |  |  |  |  |",
+                "   +--+--+--+--+--+",
+            ]
+        )
+        normalized = normalize_board_for_display(
+            puzzle_type="pattern",
+            problem_ascii=board,
+            board_ascii=board,
+        )
+        lines = normalized.splitlines()
+        self.assertEqual(lines.count("   +--+--+--+--+--+"), 6)
+        self.assertEqual(lines[2], "   +--+--+--+--+--+")
+        self.assertEqual(lines[-1], "   +--+--+--+--+--+")