Reject two-line angular constraints over 180 degrees that can never be satisfied (#73) (#190)

crates/constraints/src/residual.rs

@@ -244,7 +244,10 @@ impl Built {
                     return need("two lines or an arc");
                 }
                 b.target = target.to_radians();
-                if !b.target.is_finite() || b.target.abs() > std::f64::consts::TAU {
+                // Two lines measure a signed angle in [-180, 180] and the sign is re-read from the geometry, so a larger
+                // target would flip the sign once solved and never be satisfied; only an arc sweep can reach a full turn.
+                let max = if b.form == Form::LL { std::f64::consts::PI } else { std::f64::consts::TAU };
+                if !b.target.is_finite() || b.target.abs() > max {
                     return Err("angle out of range".into());
                 }
             }

crates/constraints/src/tests.rs

@@ -155,6 +155,19 @@ fn symmetric_fix() {
     ok(&mut d, con(ConstraintKind::Symmetric, &[w(p), w(q), w(axis)]));
 }
 
+#[test]
+fn two_line_angle_over_180_is_rejected() {
+    let mut d = Drawing::default();
+    let a = line(&mut d, (0.0, 0.0), (10.0, 0.0));
+    let b = line(&mut d, (0.0, 0.0), (0.0, 5.0));
+    let before = (ln(&d, a), ln(&d, b));
+    assert!(add(&mut d, dim(ConstraintKind::Angular, &[w(a), w(b)], "", "200"), &SolveOptions::default()).is_err());
+    assert!(d.constraints.is_empty());
+    assert_eq!((ln(&d, a), ln(&d, b)), before);
+    ok(&mut d, dim(ConstraintKind::Angular, &[w(a), w(b)], "", "180"));
+    assert!(all_satisfied(&d));
+}
+
 #[test]
 fn dimensional_constraints() {
     let mut d = Drawing::default();