Don't allow extra keys in top schema model

schema.json

@@ -155,7 +155,7 @@
       "type": "object"
     },
     "Cv": {
-      "additionalProperties": true,
+      "additionalProperties": false,
       "properties": {
         "name": {
           "anyOf": [
@@ -4986,6 +4986,7 @@
           "description": "Vertical space between text-based entries. It can be specified with units (cm, in, pt, mm, ex, em). For example, `0.1cm`. The default value is `0.3em`."
         },
         "show_time_spans_in": {
+          "default": [],
           "description": "Section titles where time spans (e.g., '2 years 3 months') should be displayed. The default value is `[]`.",
           "items": {
             "type": "string"
@@ -5017,6 +5018,7 @@
           "description": "Vertical space between text-based entries. It can be specified with units (cm, in, pt, mm, ex, em). For example, `0.1cm`. The default value is `0.15cm`."
         },
         "show_time_spans_in": {
+          "default": [],
           "description": "Section titles where time spans (e.g., '2 years 3 months') should be displayed. The default value is `[]`.",
           "items": {
             "type": "string"
@@ -5048,6 +5050,7 @@
           "description": "Vertical space between text-based entries. It can be specified with units (cm, in, pt, mm, ex, em). For example, `0.1cm`. The default value is `0.3em`."
         },
         "show_time_spans_in": {
+          "default": [],
           "description": "Section titles where time spans (e.g., '2 years 3 months') should be displayed. The default value is `[]`.",
           "items": {
             "type": "string"
@@ -5079,6 +5082,7 @@
           "description": "Vertical space between text-based entries. It can be specified with units (cm, in, pt, mm, ex, em). For example, `0.1cm`. The default value is `0.3em`."
         },
         "show_time_spans_in": {
+          "default": [],
           "description": "Section titles where time spans (e.g., '2 years 3 months') should be displayed. The default value is `[]`.",
           "items": {
             "type": "string"
@@ -5744,7 +5748,7 @@
       "type": "string"
     }
   },
-  "additionalProperties": true,
+  "additionalProperties": false,
   "properties": {
     "cv": {
       "$ref": "#/$defs/Cv",

src/rendercv/schema/models/rendercv_model.py

@@ -2,7 +2,7 @@ import pathlib
 
 import pydantic
 
-from .base import BaseModelWithExtraKeys
+from .base import BaseModelWithoutExtraKeys
 from .cv.cv import Cv
 from .design.classic_theme import ClassicTheme
 from .design.design import Design
@@ -11,7 +11,7 @@ from .settings.settings import Settings
 from .validation_context import get_input_file_path
 
 
-class RenderCVModel(BaseModelWithExtraKeys):
+class RenderCVModel(BaseModelWithoutExtraKeys):
     # Technically, `cv` is a required field, but we don't pass it to the JSON Schema
     # so that the same schema can be used for standalone design, locale, and settings
     # files.

src/rendercv/schema/variant_pydantic_model_generator.py

@@ -9,6 +9,26 @@ from rendercv.exception import RenderCVInternalError
 type FieldSpec = tuple[type[Any], FieldInfo]
 
 
+def sanitize_defaults(value: Any) -> Any:
+    """Recursively convert CommentedMap/CommentedSeq to dict/list.
+
+    Why:
+        ruamel.yaml returns custom types that behave like dict/list but confuse Pydantic
+        and JSON schema generation. Stripping metadata ensures clean defaults.
+
+    Args:
+        value: The value to sanitize (can be nested dict/list structure).
+
+    Returns:
+        The sanitized value with standard Python types.
+    """
+    if isinstance(value, list):
+        return [sanitize_defaults(v) for v in value]
+    if isinstance(value, dict):
+        return {k: sanitize_defaults(v) for k, v in value.items()}
+    return value
+
+
 def create_variant_pydantic_model[T: pydantic.BaseModel](
     variant_name: str,
     defaults: dict[str, Any],
@@ -50,6 +70,9 @@ def create_variant_pydantic_model[T: pydantic.BaseModel](
     """
     validate_defaults_against_base(defaults, base_class, variant_name)
 
+    # Sanitize defaults to remove ruamel.yaml metadata
+    defaults = sanitize_defaults(defaults)
+
     field_specs: dict[str, Any] = {}
     base_fields = base_class.model_fields