homericintelligence/.claude-plugin/skills/config-default-model-drift

Skill: config-default-model-drift

Overview

| Field | Value | |-------------|------------------------------------------------------------------------| | Date | 2026-02-20 | | Issue | #793 | | PR | #838 | | Objective | Eliminate hardcoded model-ID literals that silently drift from config | | Outcome | Success — single source of truth in config/defaults.yaml | | Category | architecture |

When to Use

Trigger when you see any of the following:

• Hardcoded model-ID string literals (e.g. "claude-opus-4-5-20251101") in CLI or orchestrator code
• model or "<literal>" fallback patterns instead of reading from config
• Follow-up issues noting that a previous refactor missed a stale literal
• A new default model has been adopted but code still references the old one
• Audit findings of literals that will "silently fall out of sync" with a config file

Verified Workflow

1. Locate every hardcoded literal

grep -rn "claude-opus-4-5" scylla/

Expect: scylla/cli/main.py and scylla/orchestrator.py (possibly docstrings too).

2. Add default_model to config/defaults.yaml

# Default model used when no --model flag is provided
default_model: "claude-opus-4-5-20251101"

Place it at the top level (not nested under a section).

3. Add the Pydantic field to DefaultsConfig

In scylla/config/models.py, inside DefaultsConfig:

default_model: str = Field(
    default="claude-opus-4-5-20251101",
    description="Default model ID when none is specified",
)

The Python-level default keeps backward-compat for callers that don't supply the YAML key (e.g. test fixtures that use a trimmed defaults.yaml).

4. Update the CLI

In scylla/cli/main.py:

# Before (stale literal)
model_id = model or "claude-opus-4-5-20251101"

# After (reads from config)
from scylla.config import ConfigLoader
model_id = model or ConfigLoader().load_defaults().default_model

ConfigLoader() with no arguments resolves relative to Path(".") (the cwd at runtime).

5. Update docstrings / examples

In scylla/orchestrator.py the class docstring had a copy of the literal as an example. Replace with ConfigLoader().load_defaults().default_model to keep it consistent and searchable.

6. Write the test

Add to tests/unit/cli/test_cli.py:

def test_run_default_model_from_config(self) -> None:
    """Default model_id is read from ConfigLoader, not a hardcoded literal."""
    sentinel_model = "test-model-from-config"

    mock_defaults = MagicMock()
    mock_defaults.default_model = sentinel_model

    mock_loader_instance = MagicMock()
    mock_loader_instance.load_defaults.return_value = mock_defaults

    captured: dict[str, str] = {}

    mock_orchestrator_instance = MagicMock()
    mock_orchestrator_instance.run_batch.return_value = []

    def capture_config(config: object) -> MagicMock:
        captured["model"] = getattr(config, "model", None)
        return mock_orchestrator_instance

    runner = CliRunner()
    with (
        patch("scylla.cli.main.ConfigLoader", return_value=mock_loader_instance),
        patch("scylla.cli.main.EvalOrchestrator", side_effect=capture_config),
    ):
        runner.invoke(cli, ["run", "001-test", "--tier", "T0", "--runs", "1"])

    assert captured.get("model") == sentinel_model

Key points:

• Mock scylla.cli.main.ConfigLoader (the import in the module under test, not the source).
• Capture OrchestratorConfig.model via side_effect=capture_config on EvalOrchestrator.
• The test is independent of config/defaults.yaml on disk — it proves the wiring, not the value.

7. Update the test fixture if needed

tests/fixtures/config/defaults.yaml does not need to be updated because DefaultsConfig has a Python-level Pydantic default for default_model. Existing fixture-based tests keep passing.

8. Run validation

pixi run python -m pytest tests/ --no-cov    # all tests pass
pre-commit run --all-files                    # all hooks pass

Failed Attempts

None in this session — the pattern was clean and straightforward.

Results & Parameters

| Parameter | Value | |-------------------|------------------------------| | Files changed | 5 | | Lines added | 41 | | Lines removed | 2 | | Tests added | 1 | | Total tests | 2267 (all passing) | | Pre-commit hooks | 13 / 13 passing |

Files Modified

| File | Change | |----------------------------------|---------------------------------------------------------| | config/defaults.yaml | Added default_model key | | scylla/config/models.py | Added default_model field to DefaultsConfig | | scylla/cli/main.py | Replaced literal with ConfigLoader().load_defaults()… | | scylla/orchestrator.py | Updated docstring example | | tests/unit/cli/test_cli.py | Added test_run_default_model_from_config |

Key Insight

When ConfigLoader() is instantiated without a base_path, it defaults to Path("."). This is fine at CLI runtime (cwd is the project root) but would fail in a unit test without mocking. Always mock scylla.cli.main.ConfigLoader (the reference in the module, not the original import path) when testing CLI code that calls ConfigLoader() at the module level.