feat(gradient): selectable gradient types + working creation

GRADIENT silently degraded to a plain hatch: add_hatch rebuilt the
render model from the DXF entity but never encoded the gradient on it,
so the committed fill lost its gradient entirely. The entity now
carries the full gradient record (name, angle, colour stops,
solid-fill flag), and the standard shape set became selectable:
Linear / Cylinder / Spherical / Hemispherical / Curved plus an Invert
toggle, offered as prompt buttons on the GRADIENT command and as a
Gradient type dropdown + Invert box in the properties panel. All nine
standard DXF names round-trip (inverted linear persists by swapping
the colour stops), and the shaders shape each kind distinctly —
mirrored cylinder, eased curve, dome-profiled hemisphere — on both the
native and web pipelines without changing the GPU struct sizes.

Co-Authored-By: Claude Fable 5 <[email protected]>

src/modules/draw/draw/hatch.rs

@@ -375,6 +375,10 @@ pub struct GradientCommand {
     mode: Mode,
     manual_pts: Vec<DVec3>,
     missed: bool,
+    /// Gradient shape, switchable via the prompt options (#415).
+    kind: crate::scene::model::hatch_model::GradientKind,
+    /// Swap the two colour stops.
+    invert: bool,
 }
 
 impl GradientCommand {
@@ -384,6 +388,8 @@ impl GradientCommand {
             mode: Mode::PickInside,
             manual_pts: vec![],
             missed: false,
+            kind: crate::scene::model::hatch_model::GradientKind::Linear,
+            invert: false,
         }
     }
 
@@ -394,9 +400,10 @@ impl GradientCommand {
             pattern: HatchPattern::Gradient {
                 angle_deg: 0.0,
                 color2: [0.18, 0.18, 0.18, 0.0],
-                radial: false,
+                kind: self.kind,
+                invert: self.invert,
             },
-            name: "LINEAR".into(),
+            name: self.kind.dxf_name(self.invert).into(),
             color: [0.30, 0.60, 0.95, 0.80],
             angle_offset: 0.0,
             scale: 1.0,
@@ -420,7 +427,11 @@ impl CadCommand for GradientCommand {
                 } else {
                     ""
                 };
-                format!("GRADIENT  Pick internal point:{miss}")
+                format!(
+                    "GRADIENT ({}{})  Pick internal point:{miss}",
+                    self.kind.label(),
+                    if self.invert { ", inverted" } else { "" }
+                )
             }
             Mode::Manual => {
                 if self.manual_pts.is_empty() {
@@ -435,7 +446,19 @@ impl CadCommand for GradientCommand {
     fn options(&self) -> Vec<crate::command::CmdOption> {
         use crate::command::CmdOption;
         match &self.mode {
-            Mode::PickInside => vec![CmdOption::new("Draw manually", "S")],
+            Mode::PickInside => {
+                let mut opts = vec![CmdOption::new("Draw manually", "S")];
+                for k in crate::scene::model::hatch_model::GradientKind::ALL {
+                    if k != self.kind {
+                        opts.push(CmdOption::new(k.label(), k.label()));
+                    }
+                }
+                opts.push(CmdOption::new(
+                    if self.invert { "Invert: on" } else { "Invert: off" },
+                    "I",
+                ));
+                opts
+            }
             Mode::Manual => {
                 // Enter accepts the boundary once at least 3 points are picked.
                 if self.manual_pts.len() >= 3 {
@@ -493,11 +516,25 @@ impl CadCommand for GradientCommand {
     }
 
     fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
-        if text.trim().eq_ignore_ascii_case("s") {
+        let t = text.trim();
+        if t.eq_ignore_ascii_case("s") {
             self.mode = Mode::Manual;
             self.missed = false;
             return Some(CmdResult::NeedPoint);
         }
+        // Gradient type keywords / buttons + the invert toggle (#415).
+        if t.eq_ignore_ascii_case("i") || t.eq_ignore_ascii_case("invert") {
+            self.invert = !self.invert;
+            return Some(CmdResult::NeedPoint);
+        }
+        if let Some(k) = crate::scene::model::hatch_model::GradientKind::ALL
+            .iter()
+            .copied()
+            .find(|k| k.label().eq_ignore_ascii_case(t))
+        {
+            self.kind = k;
+            return Some(CmdResult::NeedPoint);
+        }
         None
     }