Add better control over substreams.

tests/utils/debug.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, it, vi } from 'vitest';
+import { log } from '../../src/utils/debug.js';
+
+describe('log', () => {
+  it('should do nothing without debug logging set', () => {
+    const spy = vi.spyOn(global.console, 'debug');
+    log({}, 'foo');
+    expect(spy).not.toBeCalled();
+  });
+  it('should log debug when appropriately configured', () => {
+    const spy = vi.spyOn(global.console, 'debug');
+    log({ debug: { logging: true } }, 'foo');
+    expect(spy).toBeCalledWith('foo');
+  });
+});