Geom: the bounded-sizes test also covers the cap itself, NaN, infinities and negative sizes

Review follow-up on #1774.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/geom/src/tests.rs

@@ -59,7 +59,8 @@ fn absurd_sizes_build_bounded_paths() {
     // kurbo subdivides an arc in proportion to the sixth root of its radius, so without a cap the
     // segment count grows without bound with the input: a 1e36 ellipse was about a million
     // elements and 1e60 never returned. Sizes are untrusted (files, commands), so they are capped.
-    for mag in [1e36, 1e300, f64::MAX] {
+    // At the cap itself (1e9) an arc is still a few dozen segments.
+    for mag in [MAX_COORD, 1e36, 1e300, f64::MAX] {
         let paths = [
             ("ellipse", ellipse(mag, mag, 0.0, PI, 0.0)),
             ("ring", ellipse(mag, mag, 0.0, TAU, 0.5)),
@@ -76,6 +77,19 @@ fn absurd_sizes_build_bounded_paths() {
         let p = smoothed_polygon(&[Point::new(0.0, 0.0), Point::new(mag, 0.0), Point::new(mag, mag)], mag, 0.6);
         assert!(p.elements().len() < 1_000, "huge points at {mag:e}: {} elements", p.elements().len());
     }
+    // NaN, infinities and negative sizes build nothing or a bounded path with a finite box.
+    for v in [f64::NAN, f64::INFINITY, f64::NEG_INFINITY, -1e36, -1.0] {
+        let paths = [
+            ("ellipse", ellipse(v, v, v, v, v)),
+            ("rounded_rect", rounded_rect(v, v, [v; 4], v)),
+            ("smoothed_polygon", smoothed_polygon(&polygon_points(100.0, 100.0, 5), v, v)),
+        ];
+        for (name, p) in paths {
+            assert!(p.elements().len() < 1_000, "{name} at {v}: {} elements", p.elements().len());
+            let b = p.bounding_box();
+            assert!([b.x0, b.y0, b.x1, b.y1].iter().all(|x| x.is_finite()), "{name} at {v}: {b:?}");
+        }
+    }
     // Sizes a document can hold are untouched.
     let p = rounded_rect(1e6, 1e6, [1e5; 4], 0.6);
     let b = p.bounding_box();