fix: unfold sheets shrunk by a parameter change (#349)

A sheet-metal tray built at 2000 x 2500 mm with an edge flange on all four
edges (72° or 90°) and unfolded failed to rebuild when W and H went to
400 x 300, 600 x 450, or W alone to 400: "planar region arrangement failed
or exceeded its bounded processing budget". The same tray drawn at 400 x 300
unfolded, and growing it worked.

The sketch solved again after the change leaves its corners ~1e-13 mm off,
so the flanges inherit a hair of tilt and their panels and bend zones meet
the trimmed base within 1e-13 mm instead of exactly. The flat pattern is a
balanced union of those pieces, and the arrangement chains its output loops
within 10 tol. In a later round, ray parity classified a bend zone's edge
midpoint that lay level with a corner whose two lines did not quite meet:
the ray slipped through the gap without a crossing, the zone's edges counted
as inside the other operand and were dropped, and the outline no longer
closed. A rectangle turned by 1e-14 rad failed the same way.

inside_loop now closes the gap where one line ends and the next begins with
a straight connector while it counts crossings; exactly closed joints are
unaffected. Joints with an arc keep the arc's own endpoint rule, which
treats ends within its angular tolerance as on the ray (a connector there
double counted at a circle split into two arcs).

Co-authored-by: NOWN-DEV <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

crates/engine/src/cmd/sheet_tests.rs

@@ -702,6 +702,45 @@ fn fold_keeps_the_larger_side_either_way() {
     }
 }
 
+/// A tray shrunk by a parameter change unfolds like the same tray built at that size. The
+/// sketch solved again leaves its corners ~1e-13 mm off, and the flat pattern's planar
+/// arrangement used to drop a bend zone through a gap that small: "planar region arrangement
+/// failed", for W alone or both sizes, at 72° or 90°, while growing the tray worked.
+#[test]
+fn tray_shrunk_by_a_parameter_unfolds_like_one_built_at_that_size() {
+    for angle in [72.0, 90.0] {
+        let tray = |s: &mut Session, w: f64, h: f64| {
+            run(s, "parameters.add", json!({"name": "W", "expression": format!("{w} mm")}));
+            run(s, "parameters.add", json!({"name": "H", "expression": format!("{h} mm")}));
+            run(s, "sheet.manage_rules", json!({"name": "AL2", "thickness": "2 mm", "k_factor": "0.5", "bend_radius": "1 mm", "active": true}));
+            run(s, "sketch.create", json!({"plane": "XY", "name": "Tray"}));
+            run(s, "sketch.rectangle.two_point", json!({"p0": [0, 0], "p1": [w, h]}));
+            run(s, "sketch.constraint.fix", json!({"entities": ["p1"]}));
+            run(s, "sketch.dimension", json!({"entities": ["l1"], "value": "W"}));
+            run(s, "sketch.dimension", json!({"entities": ["l2"], "value": "H"}));
+            run(s, "sketch.finish", json!({}));
+            run(s, "sheet.flange", json!({"type": "base", "sketch": "Tray"}));
+            let edges = json!([[w / 2.0, 0, 2], [w, h / 2.0, 2], [w / 2.0, h, 2], [0, h / 2.0, 2]]);
+            run(s, "sheet.flange", json!({"type": "edge", "edges": edges, "height": 38.6, "angle": angle}));
+            run(s, "sheet.unfold", json!({}));
+        };
+        let mut direct = Session::default();
+        tray(&mut direct, 400.0, 300.0);
+        let want = flat(&mut direct)["flat_size_mm"].clone();
+        let mut shrunk = Session::default();
+        tray(&mut shrunk, 2000.0, 2500.0);
+        for (name, expr) in [("W", "400 mm"), ("H", "300 mm")] {
+            let r = run(&mut shrunk, "parameters.change", json!({"name": name, "expression": expr}));
+            assert_eq!(r["errors"], json!([]), "{angle}° {name} = {expr}: {r}");
+        }
+        let got = flat(&mut shrunk)["flat_size_mm"].clone();
+        for k in 0..3 {
+            assert!((got[k].as_f64().unwrap() - want[k].as_f64().unwrap()).abs() < 1e-9, "{angle}°: {got} {want}");
+        }
+        assert!(rel(volume(&mut shrunk), volume(&mut direct)) < 1e-9, "{angle}°");
+    }
+}
+
 #[test]
 fn bend_table_exports_shop_dimensions_and_tracks_parameter_changes() {
     let mut s = Session::default();