Rests and holidays 湯治
A week away should not cost you the habit. What a rest does to your schedule, and why it moves your due dates instead of stopping the clock.
Spaced repetition punishes absence. That is not a design choice anybody made - it falls out of the arithmetic. Every day you are away, more cards come due, and none of them go away. Leave for a fortnight and you return to a queue that took a fortnight to build.
This is the point at which most people quit, and it is worth being precise about why. It is not the hard days that end a habit. It is opening the app after a holiday, seeing eight hundred cards waiting, closing it, and never opening it again. A learner who cannot leave without being punished for it eventually leaves for good.
What a rest does
A rest 湯治 convalescence at the hot springs moves your schedule rather than stopping the clock. When you come back, every due date shifts forward by exactly the span that was frozen.
So the queue you left is the queue you return to. A card that was two days overdue when you departed is two days overdue when you return. One that was due next Tuesday is still a week out. Nothing has piled up, and nothing has been skipped either - the schedule was carried, not cancelled.
The distinction matters because the obvious implementation is to pause reviews and let the dates stand. That does not work: it produces exactly the backlog it was meant to prevent, just with a nicer name on it.
What it costs
Nothing, on return. Your streak survives. Your progress is untouched. There is no catch-up period and no penalty afterwards.
Two things are true while you are away. You give up your seat on the 番付 ranking board until you are back - the board is a picture of who is travelling now, and holding a place on it while resting would make it a picture of something else. And a rest is bounded when you take it: you choose 7, 14 or 30 days, and it never extends itself - 30 is the longest a single rest may run.
Come back late and the shift is still only the rest you asked for. The days past it are ordinary absence, which is what stops this from being a permanent pause on a streak that is no longer being earned.
Why it is free
It used to want a plan, on the reasoning that it costs us nothing to serve - two columns and one database update. Costing nothing to serve turned out to be a poor reason to charge for it: a learner who cannot take a week off without coming back to a fortnight of debt is a learner who quits, and no schedule is improved by that.
A rest changes no due date that a traveler could not change by simply coming back and working through the queue. What it buys is not having to.
The scheduler underneath
None of this needs a special case in the scheduling algorithm. EdoQuest schedules with FSRS, which only ever reads a card's next due date - so moving that date forward is the whole of the mechanism. There is no separate holiday mode inside the scheduler, and nothing to drift out of step with it.