Perpendicular Plane (construct.plane.perpendicular {plane, line}): the plane through a straight edge, sketch line or axis, square to a plane or planar face; a line square to the plane is refused (no single answer)

Fixes #20

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

crates/engine/src/cmd/construct.rs

@@ -83,6 +83,9 @@ pub static COMMANDS: &[CommandSpec] = &[
         .at("SOLID", "CONSTRUCT")
         .icon("plane")
         .params("path: edge or sketch curve ref; t: expr, 0…1 along it (default 0.5); name? The plane is square to the path there"),
+    CommandSpec::new("construct.plane.perpendicular", "Perpendicular Plane", plane_perpendicular).at("SOLID", "CONSTRUCT").icon("plane").params(
+        "plane: plane or planar face ref; line: straight edge, sketch line or axis ref; name? The plane holds the line and is square to the plane",
+    ),
 ];
 
 /// A reference from its JSON form.
@@ -249,3 +252,9 @@ fn plane_along(s: &mut Session, p: &Value) -> Result<Value> {
     let t = t_param(s, p, cmd)?;
     plane(s, p, PlaneRef::AlongPath { path: Box::new(path), t })
 }
+
+fn plane_perpendicular(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "construct.plane.perpendicular";
+    let (base, line) = (geo(s, p.get("plane"), cmd, "plane")?, geo(s, p.get("line"), cmd, "line")?);
+    plane(s, p, PlaneRef::Perpendicular { plane: Box::new(base), line: Box::new(line) })
+}