```ts
export function applyOverrides(base: Record<string, string>, overrides: string[]): Record<string, string> {
  if (!Array.isArray(overrides)) {
    throw new Error("overrides must be a list");
  }

  const merged = { ...base };

  for (const override of overrides) {
    const [name, value] = override.split('=', 2);

    if (!value || !override.includes('=')) {
      throw new Error("Each override must be in the form 'name=value'");
    }

    if (!base[name]) {
      throw new Error(`Base does not have setting '${name}'`);
    }

    merged[name] = value;
  }

  return merged;
}
```