feat(commands): prompt for a system-variable value on the next line

Typing a bare system-variable name (MIRRTEXT, FILLMODE, LTSCALE, …) now
echoes the current value and prompts "Enter new value for <NAME> <cur>:",
capturing the next command-line entry as the new value — Enter keeps the
current one, Escape cancels. The single-line "MIRRTEXT 1" form still works.
Mirrors the awaiting_vports pattern: a pending_setvar field on the app,
consumed at the top of on_command_submit.

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

src/app/commands/styleprops.rs

@@ -1213,8 +1213,17 @@ impl OpenCADStudio {
                         Ok((msg, changed)) => {
                             if changed {
                                 self.tabs[i].dirty = true;
+                                self.command_line.push_output(&msg);
+                            } else {
+                                // Queried with no value (`changed == false`):
+                                // prompt for a new value on the next line instead
+                                // of only echoing the current one. Enter keeps it.
+                                let current = msg.split('=').nth(1).map(str::trim).unwrap_or("");
+                                self.command_line.push_output(&format!(
+                                    "Enter new value for {name} <{current}>:"
+                                ));
+                                self.pending_setvar = Some(name.clone());
                             }
-                            self.command_line.push_output(&msg);
                         }
                         Err(e) => self.command_line.push_error(&e),
                     }

src/app/mod.rs

@@ -274,6 +274,10 @@ pub(super) struct OpenCADStudio {
     /// `true` after a bare `VPORTS` in model space — the next command-line
     /// entry is treated as the tiled-config option (SIngle/2H/2V/4).
     awaiting_vports: bool,
+    /// Set to the variable name after a bare system-variable query (e.g. a lone
+    /// `MIRRTEXT`) — the next command-line entry is its new value, empty keeps
+    /// the current one.
+    pending_setvar: Option<String>,
     /// Cursor is hovering over the UCS icon body — drives the hover highlight.
     ucs_icon_hover: bool,
     /// UCS icon is selected (clicked): its grips are shown and draggable.
@@ -1958,6 +1962,7 @@ impl OpenCADStudio {
             default_bg_color: None,
             default_paper_bg_color: None,
             awaiting_vports: false,
+            pending_setvar: None,
             ucs_icon_hover: false,
             ucs_icon_selected: false,
             ucs_grip_drag: None,

src/app/update/command.rs

@@ -178,6 +178,17 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                     };
                     return self.dispatch_command(&format!("VPORTS {cfg}"));
                 }
+                // Interactive system-variable value: after a bare `MIRRTEXT`
+                // (etc.) the next entry is the new value; empty Enter keeps the
+                // current setting.
+                if let Some(name) = self.pending_setvar.take() {
+                    let val = self.command_line.input.trim().to_string();
+                    self.command_line.input.clear();
+                    if val.is_empty() {
+                        return Task::none();
+                    }
+                    return self.dispatch_command(&format!("SETVAR {name} {val}"));
+                }
                 // If the user navigated the autocomplete list with the
                 // arrow keys, Enter dispatches the highlighted command
                 // rather than the partial text actually in the buffer.
@@ -414,6 +425,11 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                 if self.pane_move_from.take().is_some() {
                     return Task::none();
                 }
+                // Esc cancels a pending system-variable value prompt.
+                if self.pending_setvar.take().is_some() {
+                    self.command_line.push_info("*Cancel*");
+                    return Task::none();
+                }
                 // UCS icon: Esc ends any grip drag and clears the selection
                 // (only when no command owns Escape).
                 if self.tabs[self.active_tab].active_cmd.is_none()