```ts
/**
 * a divided by b, safely handling division by zero and non-finite numbers.
 */
export function safeDivide(a: number, b: number): number {
  if (!Number.isFinite(a) || !Number.isFinite(b)) {
    throw new Error("Both arguments must be finite numbers.");
  }
  if (b === 0 || b === -0) {
    throw new Error("Divisor cannot be zero.");
  }
  return a / b;
}
```