fix(parsing): parse extra field types

src/opencode_ai/_models.py

@@ -208,14 +208,18 @@ class BaseModel(pydantic.BaseModel):
             else:
                 fields_values[name] = field_get_default(field)
 
+        extra_field_type = _get_extra_fields_type(__cls)
+
         _extra = {}
         for key, value in values.items():
             if key not in model_fields:
+                parsed = construct_type(value=value, type_=extra_field_type) if extra_field_type is not None else value
+
                 if PYDANTIC_V2:
-                    _extra[key] = value
+                    _extra[key] = parsed
                 else:
                     _fields_set.add(key)
-                    fields_values[key] = value
+                    fields_values[key] = parsed
 
         object.__setattr__(m, "__dict__", fields_values)
 
@@ -370,6 +374,23 @@ def _construct_field(value: object, field: FieldInfo, key: str) -> object:
     return construct_type(value=value, type_=type_, metadata=getattr(field, "metadata", None))
 
 
+def _get_extra_fields_type(cls: type[pydantic.BaseModel]) -> type | None:
+    if not PYDANTIC_V2:
+        # TODO
+        return None
+
+    schema = cls.__pydantic_core_schema__
+    if schema["type"] == "model":
+        fields = schema["schema"]
+        if fields["type"] == "model-fields":
+            extras = fields.get("extras_schema")
+            if extras and "cls" in extras:
+                # mypy can't narrow the type
+                return extras["cls"]  # type: ignore[no-any-return]
+
+    return None
+
+
 def is_basemodel(type_: type) -> bool:
     """Returns whether or not the given type is either a `BaseModel` or a union of `BaseModel`"""
     if is_union(type_):

src/opencode_ai/types/config.py

@@ -57,6 +57,7 @@ class Mode(BaseModel):
 
     plan: Optional[ModeConfig] = None
 
+    __pydantic_extra__: Dict[str, ModeConfig] = FieldInfo(init=False)  # pyright: ignore[reportIncompatibleVariableOverride]
     if TYPE_CHECKING:
         # Stub to indicate that arbitrary properties are accepted.
         # To access properties that are not valid identifiers you can use `getattr`, e.g.