Fix #683: Preferences > Type > Additional Fonts Folder

VectorCraft found fonts only in the system's font folders (and, on Windows,
those font services activate). A new preference names one more folder, read
with its subfolders after the platform's: its fonts are listed in the font
menus and used as if installed, without installing them.

- vectorcraft_text::set_user_font_dirs / user_font_dirs: folders
  system_font_dirs adds to every scan (none on wasm).
- prefs fontsFolder (Type > Options > Additional Fonts Folder), trimmed; when
  it changes after the first scan, the fonts are scanned again at once, so the
  folder's fonts appear (or go) and type in them lays out again.
- The label is translated where Additional Plug-ins Folder is.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/fonts.rs

@@ -247,7 +247,7 @@ fn font_list(_: &mut Session, p: &Value) -> Result<Value> {
     }
 }
 
-fn rescan(s: &mut Session, _: &Value) -> Result<Value> {
+pub(crate) fn rescan(s: &mut Session, _: &Value) -> Result<Value> {
     let db = vectorcraft_text::FontDb::global();
     #[cfg(not(target_arch = "wasm32"))]
     let faces = db.load_system_fonts();
@@ -283,6 +283,21 @@ fn rescan(s: &mut Session, _: &Value) -> Result<Value> {
 mod tests {
     use super::*;
 
+    /// Type › Options › Additional Fonts Folder (#683) adds its folder to the system font scan,
+    /// trimmed; clearing it takes the folder out again.
+    #[test]
+    fn the_additional_fonts_folder_joins_the_font_scan() {
+        let mut s = Session::new();
+        let dir = std::env::temp_dir().join("vectorcraft-fonts-folder-pref");
+        s.execute("prefs.set", &json!({"key": "fontsFolder", "value": format!("  {}  ", dir.display())})).unwrap();
+        assert_eq!(vectorcraft_text::user_font_dirs(), std::slice::from_ref(&dir));
+        if !cfg!(target_arch = "wasm32") {
+            assert!(vectorcraft_text::system_font_dirs().contains(&dir));
+        }
+        s.execute("prefs.set", &json!({"key": "fontsFolder", "value": ""})).unwrap();
+        assert!(vectorcraft_text::user_font_dirs().is_empty() && !vectorcraft_text::system_font_dirs().contains(&dir));
+    }
+
     #[test]
     fn list_flag_missing_replace_and_select() {
         let mut s = Session::new();

crates/engine/src/cmd/prefscmds.rs

@@ -187,6 +187,7 @@ pub const PREF_SPECS: &[PrefSpec] = &[
     p!("missingGlyphProtection", "Type", "Options", "Enable Missing Glyph Protection", bool),
     p!("highlightAlternateGlyphs", "Type", "Options", "Highlight Alternate Glyphs", bool),
     p!("placeholderText", "Type", "Options", "Fill New Type Objects With Placeholder Text", bool),
+    p!("fontsFolder", "Type", "Options", "Additional Fonts Folder", text),
     // Units
     p!("unitsGeneral", "Units", "", "General", choice(UNITS)),
     p!("unitsStroke", "Units", "", "Stroke", choice(UNITS)),
@@ -460,7 +461,18 @@ impl Session {
         let grid_changed = p.gridline_every != self.prefs.gridline_every || p.grid_subdivisions != self.prefs.grid_subdivisions;
         let history_changed = p.history_states != self.prefs.history_states;
         let tile_edge_changed = p.pattern_tile_edge_color != self.prefs.pattern_tile_edge_color;
+        let fonts_folder_changed = p.fonts_folder != self.prefs.fonts_folder;
         self.prefs = p;
+        if fonts_folder_changed {
+            let folder = self.prefs.fonts_folder.trim();
+            vectorcraft_text::set_user_font_dirs(if folder.is_empty() { vec![] } else { vec![folder.into()] });
+            // Once the fonts were scanned, scan again now: the folder's fonts appear (or go) in the
+            // font menus, and type in them lays out again. The first scan reads it anyway.
+            if vectorcraft_text::FontDb::global().installed_fonts_changed() {
+                // Its result only counts the faces cataloged.
+                let _ = super::fonts::rescan(self, &serde_json::Value::Null);
+            }
+        }
         vectorcraft_render::set_default_threads(u16::try_from(self.prefs.render_threads).ok());
         for st in &mut self.docs {
             if history_changed {