fix: block model config writes when legacy aliases omit provider

Raise LegacyModelConfigMigrationError from ModelRepository.load() when
on-disk model_configs.yaml entries lack a required provider field, so
CLI and agent flows fail fast instead of treating the file as empty and
overwriting legacy aliases on add.

Author: nabinchha

packages/data-designer/src/data_designer/cli/controllers/model_controller.py

@@ -7,7 +7,7 @@
 from typing import TYPE_CHECKING
 
 from data_designer.cli.forms.model_builder import ModelFormBuilder
-from data_designer.cli.repositories.model_repository import ModelRepository
+from data_designer.cli.repositories.model_repository import LegacyModelConfigMigrationError, ModelRepository
 from data_designer.cli.repositories.provider_repository import ProviderRepository
 from data_designer.cli.services.model_service import ModelService
 from data_designer.cli.services.provider_service import ProviderService
@@ -54,7 +54,11 @@ def run(self) -> None:
         console.print()
 
         # Check for existing configuration
-        models = self.model_service.list_all()
+        try:
+            models = self.model_service.list_all()
+        except LegacyModelConfigMigrationError as e:
+            print_error(str(e))
+            return
 
         if models:
             self._show_existing_config()

packages/data-designer/src/data_designer/cli/repositories/model_repository.py

@@ -4,6 +4,7 @@
 from __future__ import annotations
 
 from pathlib import Path
+from typing import Any
 
 from pydantic import BaseModel
 
@@ -13,12 +14,41 @@
 from data_designer.config.utils.io_helpers import load_config_file, save_config_file
 
 
+class LegacyModelConfigMigrationError(ValueError):
+    """Raised when on-disk model configs omit the required ``provider`` field."""
+
+
 class ModelConfigRegistry(BaseModel):
     """Registry for model configurations."""
 
     model_configs: list[ModelConfig]
 
 
+def _aliases_missing_provider(config_dict: Any) -> list[str]:
+    if not isinstance(config_dict, dict):
+        return []
+    entries = config_dict.get("model_configs")
+    if not isinstance(entries, list):
+        return []
+    missing: list[str] = []
+    for entry in entries:
+        if not isinstance(entry, dict):
+            continue
+        if entry.get("provider") is None:
+            alias = entry.get("alias")
+            missing.append(str(alias) if alias is not None else "<unknown>")
+    return missing
+
+
+def _format_missing_provider_message(aliases: list[str]) -> str:
+    alias_list = ", ".join(f"'{alias}'" for alias in aliases)
+    return (
+        f"model_configs.yaml contains model alias(es) missing a required 'provider' field: {alias_list}. "
+        "Add an explicit provider name to each alias before saving changes "
+        "(edit the file directly or run `data-designer config models` after updating it)."
+    )
+
+
 class ModelRepository(ConfigRepository[ModelConfigRegistry]):
     """Repository for model configurations."""
 
@@ -34,6 +64,14 @@ def load(self) -> ModelConfigRegistry | None:
 
         try:
             config_dict = load_config_file(self.config_file)
+        except Exception:
+            return None
+
+        missing_providers = _aliases_missing_provider(config_dict)
+        if missing_providers:
+            raise LegacyModelConfigMigrationError(_format_missing_provider_message(missing_providers))
+
+        try:
             return ModelConfigRegistry.model_validate(config_dict)
         except Exception:
             return None

packages/data-designer/src/data_designer/cli/utils/agent_introspection.py

@@ -12,7 +12,7 @@
 
 import data_designer.config as dd
 from data_designer.cli.agent_command_defs import AGENT_COMMANDS
-from data_designer.cli.repositories.model_repository import ModelRepository
+from data_designer.cli.repositories.model_repository import LegacyModelConfigMigrationError, ModelRepository
 from data_designer.cli.repositories.persona_repository import PersonaRepository
 from data_designer.cli.repositories.provider_repository import ProviderRepository
 from data_designer.cli.services.download_service import DownloadService
@@ -295,7 +295,14 @@ def _get_source_file(cls: type) -> str:
 def _load_registry(repo: Any) -> Any:
     if not repo.exists():
         return None
-    registry = repo.load()
+    try:
+        registry = repo.load()
+    except LegacyModelConfigMigrationError as e:
+        raise AgentIntrospectionError(
+            code="legacy_model_config",
+            message=str(e),
+            details={"config_file": str(repo.config_file)},
+        ) from e
     if registry is None:
         raise AgentIntrospectionError(
             code="invalid_registry",

packages/data-designer/tests/cli/repositories/test_model_repository.py

@@ -3,7 +3,13 @@
 
 from pathlib import Path
 
-from data_designer.cli.repositories.model_repository import ModelConfigRegistry, ModelRepository
+import pytest
+
+from data_designer.cli.repositories.model_repository import (
+    LegacyModelConfigMigrationError,
+    ModelConfigRegistry,
+    ModelRepository,
+)
 from data_designer.config.models import ModelConfig
 from data_designer.config.utils.constants import MODEL_CONFIGS_FILE_NAME
 from data_designer.config.utils.io_helpers import save_config_file
@@ -34,3 +40,22 @@ def test_save(tmp_path: Path, stub_model_configs: list[ModelConfig]):
     repository.save(ModelConfigRegistry(model_configs=stub_model_configs))
     assert repository.load() is not None
     assert repository.load().model_configs == stub_model_configs
+
+
+def test_load_legacy_missing_provider_raises(tmp_path: Path) -> None:
+    model_configs_file_path = tmp_path / MODEL_CONFIGS_FILE_NAME
+    save_config_file(
+        model_configs_file_path,
+        {
+            "model_configs": [
+                {
+                    "alias": "legacy-alias",
+                    "model": "test-model",
+                    "inference_parameters": {"generation_type": "chat-completion"},
+                }
+            ]
+        },
+    )
+    repository = ModelRepository(tmp_path)
+    with pytest.raises(LegacyModelConfigMigrationError, match="legacy-alias"):
+        repository.load()

packages/data-designer/tests/cli/services/test_model_service.py

@@ -5,9 +5,11 @@
 
 import pytest
 
-from data_designer.cli.repositories.model_repository import ModelRepository
+from data_designer.cli.repositories.model_repository import LegacyModelConfigMigrationError, ModelRepository
 from data_designer.cli.services.model_service import ModelService
 from data_designer.config.models import ChatCompletionInferenceParams, ModelConfig
+from data_designer.config.utils.constants import MODEL_CONFIGS_FILE_NAME
+from data_designer.config.utils.io_helpers import load_config_file, save_config_file
 
 
 def test_list_all(stub_model_service: ModelService, stub_model_configs: list[ModelConfig]):
@@ -136,3 +138,31 @@ def test_delete_by_aliases_no_registry(tmp_path: Path):
     service = ModelService(ModelRepository(tmp_path))
     with pytest.raises(ValueError, match="No models configured"):
         service.delete_by_aliases(["test-alias-1"])
+
+
+def test_add_blocks_when_legacy_config_missing_provider(
+    tmp_path: Path,
+    stub_new_model_config: ModelConfig,
+) -> None:
+    """Legacy aliases without provider must block writes instead of overwriting the file."""
+    model_configs_file_path = tmp_path / MODEL_CONFIGS_FILE_NAME
+    save_config_file(
+        model_configs_file_path,
+        {
+            "model_configs": [
+                {
+                    "alias": "legacy-alias",
+                    "model": "legacy-model",
+                    "inference_parameters": {"generation_type": "chat-completion"},
+                }
+            ]
+        },
+    )
+
+    service = ModelService(ModelRepository(tmp_path))
+    with pytest.raises(LegacyModelConfigMigrationError, match="legacy-alias"):
+        service.add(stub_new_model_config)
+
+    saved = load_config_file(model_configs_file_path)
+    assert saved["model_configs"][0]["alias"] == "legacy-alias"
+    assert "provider" not in saved["model_configs"][0]