Sketch profiles: treat pieces shorter than the end join tolerance as a point (#14512)

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

crates/sketch/src/profiles.rs

@@ -1483,6 +1483,26 @@ fn island_loops(sk: &Sketch, curves: &[usize], max_edges: usize) -> Island {
             }
         }
     }
+    // A piece no longer than the end join tolerance is a point: its ends become one node. A
+    // split next to where a line touches an arc leaves such pieces, and the hairline faces they
+    // close with the line hide the profile around them (#14512).
+    let mut short: Vec<usize> = (0..nodes.len()).collect();
+    edges.retain(|e| {
+        let length = match e.seg {
+            Seg2::Line { a, b } => a.dist(b),
+            Seg2::Arc { radius, sweep, .. } => radius * sweep.abs(),
+            _ => f64::INFINITY,
+        };
+        if length > ENDPOINT_JOIN_TOL {
+            return true;
+        }
+        union(&mut short, e.u, e.v);
+        false
+    });
+    for e in &mut edges {
+        e.u = find(&mut short, e.u);
+        e.v = find(&mut short, e.v);
+    }
     let n = nodes.len();
     // One edge where pieces overlap, then prune dangling edges.
     let mut alive = without_overlaps(&edges, tol);