fn initial_schedule_cursor(
start_secs: i64,
interval_secs: i64,
) -> Result<i64, Error>Expand description
Initial scheduler cursor for start_scheduled_loop: exactly one interval
before start_secs so the first due scheduled time is start_secs itself.
Fallible: a start_secs - interval_secs difference that does not fit in
i64 is an explicit error instead of a saturated cursor that would make
the first due scheduled time start_secs + interval_secs and silently skip
the start_secs tick.