picture.corrections: a tiny sharpen value no longer panics in the blur (#3646) (#3830)

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/objects.rs

@@ -130,7 +130,8 @@ pub fn specs() -> Vec<CommandSpec> {
                 }
                 if sharpen > 0.0 {
                     img = img.unsharpen(1.0 + sharpen / 50.0, 2);
-                } else if sharpen < 0.0 {
+                } else if sharpen < 0.0 && (-sharpen / 25.0).is_normal() {
+                    // `blur` asserts on a subnormal width.
                     img = img.blur(-sharpen / 25.0);
                 }
                 img
@@ -2010,6 +2011,17 @@ mod tests {
         assert!(s.run("picture.crop", &json!({"left": 0.1})).is_err());
     }
 
+    /// A `sharpen` too small to be a normal blur width must not reach the blur, which asserts on it.
+    #[test]
+    fn a_tiny_sharpen_value_does_not_panic() {
+        let mut s = Session::new(wordcraft_doc::Document::new());
+        let data = super::super::insert::base64_encode(&png(20, 10));
+        s.run("insert.picture", &json!({"data": data})).unwrap();
+        for sharpen in [-1e-40_f64, -1e-45, -1e-38, 1e-40, -1e-30, 0.0, -0.5] {
+            s.run("picture.corrections", &json!({"sharpen": sharpen})).unwrap_or_else(|e| panic!("sharpen {sharpen}: {e:?}"));
+        }
+    }
+
     /// Transparency is absolute from the original pixels: 80% then 0% is opaque again
     /// (it used to stay faded), and repeating a value is idempotent. Corrections and color
     /// re-set the same way: brightness 0 and saturation 100 restore the original.