fix: Validate date after duration offset

[FrederikBolding]

Cronjob execution dates configured using durations can technically overflow and cause unexpected behaviour. We can catch this by asserting isValid.

---

Note

Low Risk
Small change to cron schedule parsing with clearer errors on edge-case durations; no auth or data-path changes.

Overview
Cronjob scheduling now rejects ISO 8601 durations that produce an invalid execution time after adding them to “now”, instead of returning a bad date.

Duration handling in getExecutionDate is folded into the same try/catch as cron parsing. After DateTime.now().plus(validatedDuration), an assert(offsetDate.isValid) runs so overflow cases (e.g. P1000000Y) fail with the existing “Unable to parse …” error. A test covers that extreme duration.

^{Reviewed by Cursor Bugbot for commit 13cd74c. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.59%. Comparing base (2c8a299) to head (13cd74c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4124   +/-   ##
=======================================
  Coverage   98.59%   98.59%           
=======================================
  Files         429      429           
  Lines       12495    12497    +2     
  Branches     1976     1976           
=======================================
+ Hits        12320    12322    +2     
  Misses        175      175           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[MajorLift]

What do you think about triggering a type error as well with something like:

 import { DateTime, Duration } from 'luxon';
+import type { DateTimeMaybeValid } from 'luxon';

+/**
+ * Add a duration to the current time. The sum may fall outside the
+ * representable date range, so the result may be invalid.
+ *
+ * @param duration - The duration to add.
+ * @returns The resulting date, which may be invalid.
+ */
+function getOffsetDate(duration: Duration<true>): DateTimeMaybeValid {
+  return DateTime.now().toUTC().plus(duration);
+}
+
 /**
  * Get the next execution date from a schedule, which should be either:

-      const offsetDate = DateTime.now().toUTC().plus(validatedDuration);
+      const offsetDate = getOffsetDate(validatedDuration);