fix(api): use config_to_dict() for ROMAConfig serialization in ExecutionService

[0xghost42]

Summary

Closes #71.

POST /api/v1/executions returns a 500 regardless of profile:

{"detail":"Failed to create execution: 'ROMAConfig' object is not iterable"}

The root cause was diagnosed in #74 by @nguyenhuulocbb (credit to them — no PR had been opened):

ExecutionService.start_execution falls through a hasattr(config, "model_dump") guard to dict(config) when persisting the execution record. ROMAConfig is OmegaConf-structured — it is not a Pydantic model with model_dump and is not iterable as a mapping — so the dict(config) branch raises TypeError before storage.create_execution is ever called.

Change

src/roma_dspy/api/execution_service.py:

• Use config_to_dict() from roma_dspy.config.utils. That helper already handles both ROMAConfig and plain DictConfig inputs via OmegaConf.to_container, and is the path the rest of the codebase uses for the same conversion (see get_config_diff in the same module).
• Drop the dual-branch model_dump / dict(config) ternary entirely — there is only one correct serialisation path.

-            config=config.model_dump()
-            if hasattr(config, "model_dump")
-            else dict(config),
+            config=config_to_dict(config),

tests/unit/test_execution_service.py:

• Update the mock_config_manager fixture to return a real OmegaConf.create(...) config instead of a MagicMock with a pre-canned .model_dump. The mock-based test happily walked the (broken) model_dump branch in production code, masking the regression. Returning a real config exercises the actual serialisation path.

Verification

• python3 -m py_compile clean on both touched files.
• The dict produced by config_to_dict() is JSON-serializable, which is what storage.create_execution (PostgresStorage) ultimately needs.

Out of scope

#74 also proposed adding a free_tier config profile. I left that out — free_tier is not referenced in the current README, QUICKSTART.md, or CONFIGURATION.md (the examples all use general and crypto_agent), so the issue reporter's choice of "config_profile": "free_tier" would still fail profile lookup after this fix. The fix here ensures any valid profile name now serialises correctly; adding new profiles should be a separate scoped change.

[0xghost42]

Hi @salzubi401 — gentle bump if this repo is still on your radar. PR has been open since 13/05; fixes ExecutionService serializing a Pydantic ROMAConfig with the wrong helper (uses to_dict()/dict instead of config_to_dict(), so nested models leak through). Small, scoped change. Happy to rebase or split if needed.