Legacy cron job rows may store next_run_at without timezone info.
_ensure_aware() previously stamped the Hermes-configured tz directly
via replace(tzinfo=...), which shifts absolute time when system-local
tz differs from Hermes tz — causing overdue jobs to appear not due.
Now: naive datetimes are interpreted as system-local wall time first,
then converted to Hermes tz. Aware datetimes are normalized to Hermes
tz for consistency.
Cherry-picked from PR #807, rebased onto current main.
Fixes#806
Co-authored-by: 0xNyk <0xNyk@users.noreply.github.com>
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