fix socks version issue

apps/weblibre/lib/features/proxy/data/forms/singbox_form_field.dart

@@ -26,6 +26,12 @@ enum SingboxFieldKind {
   port,
   boolean,
   stringList,
+
+  /// A value constrained to [SingboxProxyFormField.allowedValues] and always
+  /// serialized as a JSON string. Use for sing-box string enums such as the
+  /// SOCKS `version` field, whose accepted values ("4", "4a", "5") are
+  /// string-typed even when numeric-looking.
+  choice,
 }
 
 class SingboxProxyFormField {
@@ -39,6 +45,10 @@ class SingboxProxyFormField {
   final int? minValue;
   final int? maxValue;
 
+  /// Permitted values for a [SingboxFieldKind.choice] field, rendered as a
+  /// dropdown and enforced during validation.
+  final List<String>? allowedValues;
+
   const SingboxProxyFormField({
     required this.key,
     required this.label,
@@ -49,6 +59,7 @@ class SingboxProxyFormField {
     this.exactListLength,
     this.minValue,
     this.maxValue,
+    this.allowedValues,
   });
 
   bool get isSecret => kind == SingboxFieldKind.secret;
@@ -58,6 +69,7 @@ class SingboxProxyFormField {
   bool get isPort => kind == SingboxFieldKind.port;
   bool get isBoolean => kind == SingboxFieldKind.boolean;
   bool get isStringList => kind == SingboxFieldKind.stringList;
+  bool get isChoice => kind == SingboxFieldKind.choice;
 }
 
 /// Shared parsing of boolean form values. Returns null when the text doesn't

apps/weblibre/lib/features/proxy/data/forms/singbox_form_spec.dart

@@ -72,6 +72,12 @@ class SingboxProxyFormSpec {
       if (field.isBoolean && value.isNotEmpty && parseFormBool(value) == null) {
         return '${field.label} must be true or false.';
       }
+      if (field.isChoice && value.isNotEmpty) {
+        final allowedValues = field.allowedValues;
+        if (allowedValues != null && !allowedValues.contains(value)) {
+          return '${field.label} must be one of: ${allowedValues.join(', ')}.';
+        }
+      }
     }
 
     return null;

apps/weblibre/lib/features/proxy/data/forms/singbox_form_specs.dart

@@ -139,7 +139,9 @@ const singboxProxyFormSpecs = <SingboxProxyProfileType, SingboxProxyFormSpec>{
         key: 'version',
         label: 'SOCKS Version',
         defaultValue: '5',
-        kind: SingboxFieldKind.integer,
+        // sing-box expects this as a JSON string enum, not a number.
+        kind: SingboxFieldKind.choice,
+        allowedValues: ['5', '4a', '4'],
       ),
       _usernameField,
       _optionalPasswordField,

apps/weblibre/lib/features/proxy/presentation/widgets/profile_editor/structured_profile_form.dart

@@ -117,6 +117,12 @@ class _SectionFields extends StatelessWidget {
               controller: controllers[field.key]!,
               onChanged: (value) => onChanged(field.key, value),
             )
+          else if (field.isChoice)
+            _ChoiceField(
+              field: field,
+              controller: controllers[field.key]!,
+              onChanged: (value) => onChanged(field.key, value),
+            )
           else if (field.isSecret)
             ObscurableTextField(
               controller: controllers[field.key],
@@ -295,3 +301,44 @@ class _BooleanField extends HookWidget {
     );
   }
 }
+
+class _ChoiceField extends HookWidget {
+  final SingboxProxyFormField field;
+  final TextEditingController controller;
+  final ValueChanged<String> onChanged;
+
+  const _ChoiceField({
+    required this.field,
+    required this.controller,
+    required this.onChanged,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final allowedValues = field.allowedValues ?? const <String>[];
+    final value = useListenableSelector(
+      controller,
+      () => allowedValues.contains(controller.text) ? controller.text : null,
+    );
+
+    return DropdownButtonFormField<String>(
+      initialValue: value,
+      decoration: InputDecoration(
+        labelText: field.required ? '${field.label} *' : field.label,
+        helperText: field.helperText,
+        helperMaxLines: 3,
+        border: const OutlineInputBorder(),
+      ),
+      items: [
+        for (final option in allowedValues)
+          DropdownMenuItem(value: option, child: Text(option)),
+      ],
+      onChanged: (selected) {
+        if (selected != null) {
+          controller.text = selected;
+          onChanged(selected);
+        }
+      },
+    );
+  }
+}

apps/weblibre/test/features/proxy/data/models/singbox_proxy_form_test.dart

@@ -30,6 +30,34 @@ void main() {
       expect(secrets, {'password': 'secret'});
     });
 
+    test('serializes SOCKS version as a JSON string', () {
+      final spec = singboxProxyFormSpecs[SingboxProxyProfileType.socks]!;
+      final values = {
+        'server': '127.0.0.1',
+        'server_port': '9050',
+        'version': '5',
+      };
+
+      expect(spec.validate(values), isNull);
+
+      final config = jsonDecode(spec.toConfigJson(values));
+
+      // sing-box rejects a numeric version; it must be the string "5".
+      expect(config['version'], '5');
+      expect(config['version'], isA<String>());
+    });
+
+    test('rejects an out-of-range SOCKS version', () {
+      final spec = singboxProxyFormSpecs[SingboxProxyProfileType.socks]!;
+      final values = {
+        'server': '127.0.0.1',
+        'server_port': '9050',
+        'version': '6',
+      };
+
+      expect(spec.validate(values), isNotNull);
+    });
+
     test('hydrates structured values from public and secret JSON', () {
       final spec = singboxProxyFormSpecs[SingboxProxyProfileType.vless]!;