Truncate ASE swatch names that overflow the u16 length field

Found while testing crates/color/src/ase.rs:131-132

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/color/src/ase.rs

@@ -128,8 +128,14 @@ pub fn write(swatches: &[Swatch]) -> Vec<u8> {
             continue;
         }
         let mut b = Vec::new();
-        let units: Vec<u16> = s.name.encode_utf16().chain(std::iter::once(0)).collect();
-        b.extend((units.len() as u16).to_be_bytes());
+        // The length field is a u16 that counts the terminating NUL: truncate longer names.
+        let mut units: Vec<u16> = s.name.encode_utf16().take(usize::from(u16::MAX) - 1).collect();
+        // Do not leave half of a surrogate pair at the cut.
+        if units.last().is_some_and(|u| (0xD800..0xDC00).contains(u)) {
+            units.pop();
+        }
+        units.push(0);
+        b.extend(u16::try_from(units.len()).unwrap_or(u16::MAX).to_be_bytes());
         for u in units {
             b.extend(u.to_be_bytes());
         }
@@ -233,6 +239,21 @@ mod tests {
         assert_eq!(read(&write(&sw[1..])).map(|w| w.len()), Ok(MAX_COLORS), "up to the limit");
     }
 
+    #[test]
+    fn over_long_name_is_truncated_to_fit() {
+        let sw = vec![Swatch {
+            name: "x".repeat(70_000),
+            value: SwatchValue::Color { color: Color::Gray { k: 0.5 }, color_type: ColorType::Process },
+            locked: false,
+            named: true,
+            hidden: false,
+        }];
+        let back = read(&write(&sw)).unwrap();
+        assert_eq!(back.len(), 1, "the swatch must survive the round trip");
+        assert_eq!(back[0].name, "x".repeat(usize::from(u16::MAX) - 1));
+        assert_eq!(back[0].value, sw[0].value);
+    }
+
     #[test]
     fn out_of_range_components_are_clamped() {
         let mut f = Vec::new();