omop-config init fails when OA_CONFIG_PATH points at a non-existent file

[nicoloesch]

Summary

_resolve_config_path() raises FileNotFoundError at import time whenever OA_CONFIG_PATH is set to a path that doesn't exist yet. This defeats the entire purpose of init, which is supposed to create that file.

Reproduction

export OA_CONFIG_PATH=/tmp/scratch/config.toml
omop-config init

Actual behaviour

Crashes immediately with FileNotFoundError, before init's own command logic gets a chance to run at all. Root cause is in loader.py:

def _resolve_config_path() -> Path:
    raw = os.environ.get(ENV_CONFIG_PATH)
    if raw:
        p = _normalize_path(raw)
        if not p.exists():
            raise FileNotFoundError(f"{ENV_CONFIG_PATH} points to a non-existent file: {raw!r}")
        ...
        return p
    return DEFAULT_CONFIG_PATH


CONFIG_PATH: Path = _resolve_config_path()  # runs at module import

The existence check only applies on the explicit-OA_CONFIG_PATH branch. The default-path branch skips it entirely, and init there happily creates both the file and its parent directories.

Expected behaviour

omop-config init should create the file (and parent directories) at OA_CONFIG_PATH the same way it does for the default path. The existence check shouldn't apply before init has had a chance to run.

Error output

Traceback (most recent call last):
  File "/home/vscode/venv/bin/omop-config", line 4, in <module>
    from oa_configurator.cli import app
  File "/workspace/OA_Configurator/src/oa_configurator/__init__.py", line 20, in <module>
    from .io import ConfigSaveError, FLAT_ENV_PATH, save_stack_config, write_env_file
  File "/workspace/OA_Configurator/src/oa_configurator/io.py", line 14, in <module>
    from .loader import CONFIG_PATH, _normalize_path, invalidate_cache
  File "/workspace/OA_Configurator/src/oa_configurator/loader.py", line 86, in <module>
    CONFIG_PATH: Path = _resolve_config_path()
                        ^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/OA_Configurator/src/oa_configurator/loader.py", line 77, in _resolve_config_path
    raise FileNotFoundError(f"{ENV_CONFIG_PATH} points to a non-existent file: {raw!r}")
FileNotFoundError: OA_CONFIG_PATH points to a non-existent file: '/tmp/scratch/config.toml'