fix(prefs): break parse/serialize cycle for empty arrays and objects

The preferences parser treated [] and {} as strings instead of empty
array/object. On next serialize, yamlSafeString quoted them as "[]"
and "{}", permanently corrupting the preferences file. This caused
the wizard to show empty fields (models, auto_supervisor, etc.).

Fix: parseScalar now recognizes [] and {} (quoted or unquoted) as
empty array/object. Serializer omits empty values entirely instead
of writing key: [] or key: {}.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/commands.ts

@@ -448,8 +448,7 @@ function serializePreferencesToFrontmatter(prefs: Record<string, unknown>): stri
 
     if (Array.isArray(value)) {
       if (value.length === 0) {
-        lines.push(`${prefix}${key}: []`);
-        return;
+        return; // Omit empty arrays — avoids parse/serialize cycle bug with "[]" strings
       }
       lines.push(`${prefix}${key}:`);
       for (const item of value) {
@@ -480,8 +479,7 @@ function serializePreferencesToFrontmatter(prefs: Record<string, unknown>): stri
     if (typeof value === "object") {
       const entries = Object.entries(value as Record<string, unknown>);
       if (entries.length === 0) {
-        lines.push(`${prefix}${key}: {}`);
-        return;
+        return; // Omit empty objects — avoids parse/serialize cycle bug with "{}" strings
       }
       lines.push(`${prefix}${key}:`);
       for (const [k, v] of entries) {

src/resources/extensions/gsd/preferences.ts

@@ -482,16 +482,20 @@ function parseFrontmatterBlock(frontmatter: string): GSDPreferences {
   return root as GSDPreferences;
 }
 
-function parseScalar(value: string): string | number | boolean {
+function parseScalar(value: string): unknown {
   if (value === "true") return true;
   if (value === "false") return false;
+  // Recognize empty array/object literals (with or without surrounding quotes)
+  const unquoted = value.replace(/^['\"]|['\"]$/g, "");
+  if (unquoted === "[]") return [];
+  if (unquoted === "{}") return {};
   if (/^-?\d+$/.test(value)) {
     const n = Number(value);
     // Keep large integers (e.g. Discord channel IDs) as strings to avoid precision loss
     if (Number.isSafeInteger(n)) return n;
     return value;
   }
-  return value.replace(/^['\"]|['\"]$/g, "");
+  return unquoted;
 }
 
 /**