fix(cursor): clamp Windows legacy-console cursor moves at the buffer edge

CHANGELOG.md

@@ -21,6 +21,10 @@
   bytes encoded the protocol origin (panic in debug, wrap to 65535
   in release). Affects `parse_csi_normal_mouse`, `parse_csi_rxvt_mouse`,
   `parse_csi_sgr_mouse`, and `parse_csi_cursor_position`.
+- Fix integer underflow on the Windows legacy-console cursor path when the
+  requested count exceeded the current row or column (panic in debug, wrap
+  to 65535 in release). `MoveUp`, `MoveLeft`, and `MoveToPreviousLine` now
+  clamp at the first row / column, matching the ANSI path.
 - Fix `Colors::from(Colored::UnderlineColor(_))` setting the background
   color. `Colors` has no underline field, so the color is now dropped
   instead of being applied to the background.

src/cursor/sys/windows.rs

@@ -56,7 +56,7 @@ pub(crate) fn move_to(column: u16, row: u16) -> std::io::Result<()> {
 
 pub(crate) fn move_up(count: u16) -> std::io::Result<()> {
     let (column, row) = position()?;
-    move_to(column, row - count)?;
+    move_to(column, row.saturating_sub(count))?;
     Ok(())
 }
 
@@ -74,7 +74,7 @@ pub(crate) fn move_down(count: u16) -> std::io::Result<()> {
 
 pub(crate) fn move_left(count: u16) -> std::io::Result<()> {
     let (column, row) = position()?;
-    move_to(column - count, row)?;
+    move_to(column.saturating_sub(count), row)?;
     Ok(())
 }
 
@@ -98,7 +98,7 @@ pub(crate) fn move_to_next_line(count: u16) -> std::io::Result<()> {
 
 pub(crate) fn move_to_previous_line(count: u16) -> std::io::Result<()> {
     let (_, row) = position()?;
-    move_to(0, row - count)?;
+    move_to(0, row.saturating_sub(count))?;
     Ok(())
 }
 
@@ -248,6 +248,12 @@ mod tests {
         move_left(2).unwrap();
 
         assert_eq!(position().unwrap(), (0, 0));
+
+        move_to(2, 0).unwrap();
+
+        move_left(5).unwrap();
+
+        assert_eq!(position().unwrap(), (0, 0));
     }
 
     #[test]
@@ -260,6 +266,12 @@ mod tests {
         move_up(2).unwrap();
 
         assert_eq!(position().unwrap(), (0, 0));
+
+        move_to(0, 2).unwrap();
+
+        move_up(5).unwrap();
+
+        assert_eq!(position().unwrap(), (0, 0));
     }
 
     #[test]
@@ -284,6 +296,12 @@ mod tests {
         move_to_previous_line(2).unwrap();
 
         assert_eq!(position().unwrap(), (0, 0));
+
+        move_to(0, 2).unwrap();
+
+        move_to_previous_line(5).unwrap();
+
+        assert_eq!(position().unwrap(), (0, 0));
     }
 
     #[test]