feat(mtext): segmented Edit/Preview toggle, default to preview

The editor opens in preview by default and switches body views with a
segmented Edit | Preview control placed between the toolbar and the body
(active tab highlighted). All toolbar properties feed the rendered preview.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/mod.rs

@@ -737,8 +737,9 @@ pub enum Message {
     MTextAlign(mtext_editor::ParaAlign),
     /// Toolbar line-spacing change.
     MTextLineSpacing(f32),
-    /// Toggle the editor between the raw code input and the rendered preview.
-    MTextTogglePreview,
+    /// Switch the editor body between raw code input (`false`) and the
+    /// rendered preview (`true`).
+    MTextShowPreview(bool),
     /// Commit the editor: create or update the MText entity.
     MTextOk,
     /// Discard the editor without creating / changing the entity.

src/app/mtext_editor.rs

@@ -135,7 +135,7 @@ impl MTextEditorState {
             width: "1".to_string(),
             char_space: "0".to_string(),
             preview_wires: Vec::new(),
-            show_preview: false,
+            show_preview: true,
             attachment: AttachmentPoint::TopLeft,
             line_spacing: 1.0,
             // Default box ~20 characters wide; overwritten with the entity's

src/app/update.rs

@@ -3539,9 +3539,9 @@ impl OpenCADStudio {
                 self.rebuild_mtext_preview();
                 Task::none()
             }
-            Message::MTextTogglePreview => {
+            Message::MTextShowPreview(on) => {
                 if let Some(ed) = self.mtext_editor.as_mut() {
-                    ed.show_preview = !ed.show_preview;
+                    ed.show_preview = on;
                 }
                 self.rebuild_mtext_preview();
                 Task::none()

src/app/view.rs

@@ -1550,11 +1550,6 @@ fn mtext_editor_overlay<'a>(
         button(lbl("1")).on_press(Message::MTextLineSpacing(1.0)).padding(3).style(btn_style),
         button(lbl("1.5")).on_press(Message::MTextLineSpacing(1.5)).padding(3).style(btn_style),
         button(lbl("2")).on_press(Message::MTextLineSpacing(2.0)).padding(3).style(btn_style),
-        iced::widget::Space::new().width(6),
-        button(lbl(if ed.show_preview { "Code" } else { "Preview" }))
-            .on_press(Message::MTextTogglePreview)
-            .padding(3)
-            .style(btn_style),
         iced::widget::Space::new().width(Fill),
         icon_btn(include_bytes!("../../assets/icons/mt_ok.svg"), Message::MTextOk),
         icon_btn(include_bytes!("../../assets/icons/mt_cancel.svg"), Message::MTextCancel),
@@ -1562,6 +1557,37 @@ fn mtext_editor_overlay<'a>(
     .spacing(4)
     .align_y(iced::Alignment::Center);
 
+    // ── Segmented Edit | Preview toggle (between toolbar and body) ────────
+    let seg_btn = move |label: &'static str, active: bool, on: Message| -> Element<'static, Message> {
+        button(text(label).size(12).color(if active {
+            Color::WHITE
+        } else {
+            Color { r: 0.80, g: 0.80, b: 0.80, a: 1.0 }
+        }))
+        .on_press(on)
+        .padding([4, 14])
+        .style(move |_: &Theme, _| button::Style {
+            background: Some(Background::Color(if active {
+                Color { r: 0.20, g: 0.42, b: 0.72, a: 1.0 }
+            } else {
+                Color { r: 0.20, g: 0.20, b: 0.20, a: 1.0 }
+            })),
+            text_color: TEXT_COL,
+            border: Border { color: BORDER, width: 1.0, radius: 4.0.into() },
+            shadow: iced::Shadow::default(),
+            snap: false,
+        })
+        .into()
+    };
+    let toggle = container(
+        row![
+            seg_btn("Edit", !ed.show_preview, Message::MTextShowPreview(false)),
+            seg_btn("Preview", ed.show_preview, Message::MTextShowPreview(true)),
+        ]
+        .spacing(0),
+    )
+    .padding([6, 0]);
+
     // ── Body: toggles between raw code input and rendered preview ────────
     const VIEW_H: f32 = 150.0;
     let body: Element<'a, Message> = if ed.show_preview {
@@ -1604,7 +1630,7 @@ fn mtext_editor_overlay<'a>(
             .into()
     };
 
-    let panel = container(column![row1, row2, body].spacing(5))
+    let panel = container(column![row1, row2, toggle, body].spacing(5))
         .style(move |_: &Theme| container::Style {
             background: Some(Background::Color(PANEL_BG)),
             border: Border { color: BORDER, width: 1.0, radius: 5.0.into() },