Fix four things the Options survey turned up

**TEXTFILL marked the drawing modified.** It is an application preference —
it lives in a process global and is snapshotted into settings.json — but it
was missing from the list of names that persist, so setting it dirtied the
open drawing instead and never reached the settings file through that path.

**LTSCALE and CELTSCALE validated differently depending on the door.** The
standalone commands reject a value of zero or less, because a non-positive
linetype scale degenerates every dash pattern in the drawing. `SETVAR LTSCALE
-5` accepted it. A test drives both entry points for both variables and fails
on the SETVAR path without the fix.

**ISAVEBAK, SAVETIME and FILEASSOC were missing from the autocomplete
registry** although all three dispatch, so the command line never offered
them.

**`bg_color` and `paper_bg_color` were dead fields**, always written as `None`
and ignored on load since the model-space configuration superseded them.
Removing them is safe: the config is `#[serde(default)]` and ignores unknown
keys, so existing settings files simply stop carrying them.

One thing the survey flagged that turned out not to be a bug: on the Display
page the model background row hides itself outside Custom mode while the
paper and desk rows do not. That asymmetry is correct — the canvas mode
governs only the model background, and the other two apply in every mode.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/commands/mod.rs

@@ -554,6 +554,11 @@ inventory::submit!(crate::command::CommandRegistration {
         "GRIPHOT",
         "GRIPHOVER",
         "GRIPOBJLIMIT",
+        // Dispatched all along, but absent from the registry, so command-line
+        // completion never offered them.
+        "ISAVEBAK",
+        "SAVETIME",
+        "FILEASSOC",
         // Reset selected entities' overrides to follow their layer.
         "SETBYLAYER",
         // Remove duplicate objects; set drawing base point; audit integrity;

src/app/commands/styleprops.rs

@@ -1167,24 +1167,37 @@ impl OpenCADStudio {
                     let outcome: Result<(String, bool), String> = {
                         let h = &mut self.tabs[i].scene.document.header;
                         match name.as_str() {
+                            // The standalone LTSCALE and CELTSCALE commands
+                            // require a positive value; reaching the same
+                            // variable through SETVAR used to accept zero or a
+                            // negative one, which degenerates every dash
+                            // pattern in the drawing.
                             "LTSCALE" => match &value {
                                 Some(v) => v
                                     .parse::<f64>()
+                                    .ok()
+                                    .filter(|x| x.is_finite() && *x > 0.0)
                                     .map(|x| {
                                         h.linetype_scale = x;
                                         (format!("LTSCALE = {x}"), true)
                                     })
-                                    .map_err(|_| "SETVAR: numeric value required.".into()),
+                                    .ok_or_else(|| {
+                                        "SETVAR: positive numeric value required.".into()
+                                    }),
                                 None => Ok((format!("LTSCALE = {}", h.linetype_scale), false)),
                             },
                             "CELTSCALE" => match &value {
                                 Some(v) => v
                                     .parse::<f64>()
+                                    .ok()
+                                    .filter(|x| x.is_finite() && *x > 0.0)
                                     .map(|x| {
                                         h.current_entity_linetype_scale = x;
                                         (format!("CELTSCALE = {x}"), true)
                                     })
-                                    .map_err(|_| "SETVAR: numeric value required.".into()),
+                                    .ok_or_else(|| {
+                                        "SETVAR: positive numeric value required.".into()
+                                    }),
                                 None => Ok((
                                     format!("CELTSCALE = {}", h.current_entity_linetype_scale),
                                     false,
@@ -2156,6 +2169,12 @@ impl OpenCADStudio {
                                         | "GRIPHOVER"
                                         | "GRIPOBJLIMIT"
                                         | "DELOBJ"
+                                        // App-level, not part of the drawing:
+                                        // it lives in a process global and is
+                                        // snapshotted into the settings file.
+                                        // Without this it marked the drawing
+                                        // modified instead of persisting.
+                                        | "TEXTFILL"
                                 ) {
                                     self.persist_settings_if_changed();
                                 } else {
@@ -3144,3 +3163,36 @@ mod tests {
         assert_eq!(app.delete_objects, 3);
     }
 }
+
+#[cfg(test)]
+mod scale_validation_tests {
+    use crate::app::OpenCADStudio;
+
+    /// A linetype scale of zero or less degenerates every dash pattern in the
+    /// drawing, which is why the standalone commands reject it. Reaching the
+    /// same variable through SETVAR used to accept it, so which door you came
+    /// through decided whether the drawing could be broken.
+    #[test]
+    fn both_doors_to_ltscale_refuse_a_non_positive_value() {
+        for name in ["LTSCALE", "CELTSCALE"] {
+            for entry in [format!("{name} -5"), format!("SETVAR {name} -5")] {
+                let mut app = OpenCADStudio::new_for_test();
+                app.automation_op(r#"{"op":"new"}"#);
+                let i = app.active_tab;
+                let before = if name == "LTSCALE" {
+                    app.tabs[i].scene.document.header.linetype_scale
+                } else {
+                    app.tabs[i].scene.document.header.current_entity_linetype_scale
+                };
+                let _ = app.run_command_line(&entry);
+                let after = if name == "LTSCALE" {
+                    app.tabs[i].scene.document.header.linetype_scale
+                } else {
+                    app.tabs[i].scene.document.header.current_entity_linetype_scale
+                };
+                assert_eq!(before, after, "{entry} must be refused");
+            }
+        }
+    }
+}
+

src/app/settings.rs

@@ -269,12 +269,6 @@ pub struct UserSettings {
     pub pick_drag_rect: bool,
     /// Show the floating Quick Properties panel when objects are selected.
     pub quick_properties: bool,
-    /// Persisted viewport background colours (0–255 RGB); `None` = app default
-    /// (dark grey model / off-white paper). Applied to every drawing tab on
-    /// launch and to tabs opened later, so a chosen background survives restarts
-    /// (#188).
-    pub bg_color: Option<[u8; 3]>,
-    pub paper_bg_color: Option<[u8; 3]>,
     /// Interface language preference. `System` negotiates against the
     /// platform locale on every launch.
     pub language: crate::i18n::Language,
@@ -384,8 +378,6 @@ impl Default for UserSettings {
             pick_add: true,
             pick_drag_rect: false,
             quick_properties: false,
-            bg_color: None,
-            paper_bg_color: None,
             language: crate::i18n::Language::default(),
             cliprompt_lines: 3,
             commandline_fade_ms: 3000,

src/app/update/file.rs

@@ -435,8 +435,6 @@ impl OpenCADStudio {
             pick_add: self.pick_add,
             pick_drag_rect: self.pick_drag_rect,
             quick_properties: self.quick_properties,
-            bg_color: None,
-            paper_bg_color: None,
             language: self.language,
             cliprompt_lines: crate::app::settings::clamp_clipromptlines(self.cliprompt_lines),
             commandline_fade_ms: crate::app::settings::clamp_commandline_fade_ms(
@@ -516,7 +514,6 @@ impl OpenCADStudio {
         self.pick_add = s.pick_add;
         self.pick_drag_rect = s.pick_drag_rect;
         self.quick_properties = s.quick_properties;
-        // Legacy settings.bg_color / paper_bg_color are superseded by model_space config.
         if crate::i18n::set_language(s.language).is_ok() {
             self.language = s.language;
         }