fix(map): fail on blank rows inside a layer, keep trailing-space cells verbatim

src/pf1e_simulator/map.py

@@ -89,14 +89,27 @@ class _MapFile(BaseModel):
 
 
 def _split_rows(block: str, what: str, path: Path) -> tuple[str, ...]:
-    rows = tuple(line.rstrip() for line in block.splitlines() if line.strip())
-    if not rows:
+    """Split an ASCII layer into equal-width rows, failing loudly on gaps.
+
+    Trailing empty lines are a YAML block-scalar artifact and dropped; an
+    empty line *inside* the layer is a missing row -- a data error, never a
+    silently dropped one. Rows are kept verbatim (no rstrip): trailing spaces
+    are cells whenever " " is in the legend, and the width/char checks catch
+    them otherwise.
+    """
+    lines = block.splitlines()
+    while lines and lines[-1] == "":
+        lines.pop()
+    if not lines:
         msg = f"{what} layer is empty"
         raise MapValidationError(path, msg)
-    if len({len(row) for row in rows}) != 1:
+    if any(line == "" for line in lines):
+        msg = f"{what} layer has a blank row inside the layer"
+        raise MapValidationError(path, msg)
+    if len({len(row) for row in lines}) != 1:
         msg = f"{what} layer has ragged rows"
         raise MapValidationError(path, msg)
-    return rows
+    return tuple(lines)
 
 
 def _check_layer_dimensions(

tests/test_map.py

@@ -73,6 +73,35 @@ def test_rejects_ragged_rows(tmp_path: Path) -> None:
         load_map(_write(tmp_path, body))
 
 
+def test_rejects_blank_row_inside_layer(tmp_path: Path) -> None:
+    """A truly blank line inside a layer is a missing row -- an error, never
+    silently dropped (the old filter shrank the row count unnoticed)."""
+    body = _minimal_map().replace("  ###\n  #.#\n", "  ###\n\n  #.#\n")
+    with pytest.raises(MapValidationError, match="blank row"):
+        load_map(_write(tmp_path, body))
+
+
+def test_trailing_space_cells_are_kept(tmp_path: Path) -> None:
+    """With " " in the legend, trailing spaces are real cells: rstrip() must
+    not delete them (the layer keeps its full width)."""
+    body = (
+        '\nname: "Test"\nterrain: |\n  ...\n  .. \n'
+        'legend:\n'
+        '  ".": { type: floor, move_cost: 1 }\n'
+        '  " ": { type: floor, move_cost: 1 }\n'
+    )
+    spec = load_map(_write(tmp_path, body))
+    assert spec.terrain == ("...", ".. ")
+
+
+def test_rejects_trailing_space_without_legend_entry(tmp_path: Path) -> None:
+    """Without " " in the legend a padded row is ragged/unknown-char data,
+    reported as an error instead of silently stripped."""
+    body = _minimal_map().replace("  ###\n  #.#\n  ###\n", "  ### \n  #.# \n  ### \n")
+    with pytest.raises(MapValidationError):
+        load_map(_write(tmp_path, body))
+
+
 def test_rejects_non_five_foot_square_size(tmp_path: Path) -> None:
     """SRD Measuring Distance: one grid square is 5 ft; the engine geometry
     is hard-coded to that scale, so any other declared size is a load error