Machine Config: Parse and Validate Hierarchical Machine Configuration Files

Question

## Problem

Machine configurations are stored in a hierarchical format: a `base` config can be extended by `child` configs that override specific fields. Implement a system that (1) loads and merges configs (child overrides base), (2) validates required fields and value types, and (3) detects circular inheritance.

```python
class ConfigLoader:
    def load(self, config_id: str, all_configs: dict) -> dict:
        """
        all_configs = {id: {"extends": str|None, "fields": dict}}
        Returns merged, validated config or raises on error.
        """

def validate(self, merged: dict, schema: dict) -> list[str]:
        """Returns list of validation error messages."""
```

**Example:**
```
configs = {
  "base": {"extends": None, "fields": {"cpu": 4, "memory_gb": 16}},
  "gpu_worker": {"extends": "base", "fields": {"memory_gb": 64, "gpu": "A100"}}
}
loader.load("gpu_worker", configs)
# -> {"cpu": 4, "memory_gb": 64, "gpu": "A100"}
```

## Follow-ups

1. How do you detect circular inheritance? What data structure do you use?
2. What merge strategy handles list fields — replace the whole list or append?
3. How do you handle a child config referencing a non-existent base?
4. If configs are stored in a remote config service, how do you cache them safely?

Machine Config: Parse and Validate Hierarchical Machine Configuration Files

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