Unit-less parameters used as lengths read in the design's units (feature evaluation and parameter values; bare numbers stored in inputs stay mm); document.units checks what the geometry reads (Document::length_inputs) and writes the old unit (with it as the parameter's unit) into bare unit-less parameters that would move; cached results keyed on the design's units

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/engine/src/tests.rs

@@ -1467,3 +1467,15 @@ fn booleans_stay_in_their_component() {
     assert!((vol(&mut s, "BBox") - (2000.0 - 8.0 * 6.0 * 10.0)).abs() < 1e-6, "{}", vol(&mut s, "BBox"));
     assert!(s.execute("Extrude", &json!({"sketch": "Slot", "distance": 1, "operation": "cut", "participants": ["Nope"]})).is_err());
 }
+
+/// A unit-less parameter used as a length means the design's units.
+#[test]
+fn unitless_parameters_used_as_lengths_take_the_design_units() {
+    let mut s = Session::default();
+    s.doc_mut().units = "in".into();
+    run(&mut s, "parameters.add", json!({"name": "w", "expression": "2", "unit": ""}));
+    run(&mut s, "PrimitiveBox", json!({"length": "w", "width": "w * 1", "height": "10 mm"}));
+    let m = run(&mut s, "MeasureCommand", json!({}));
+    let max = |i: usize| m["bodies"][0]["bbox"]["max"][i].as_f64().unwrap_or(0.0);
+    assert!((max(0) - 50.8).abs() < 1e-9 && (max(1) - 50.8).abs() < 1e-9 && (max(2) - 10.0).abs() < 1e-9, "{m}");
+}