FSRS Compute minimum recommended retention

FSRS 4.5 was added recently, however it misses crucial metric — ability to compute minimum recommended retention.

According to the official tutorial’s Optimal Retention’s explanation:

Previously, the goal was to find the value of desired retention that would allow you to remember as much as possible within the given time constraints. Now the goal is to find the values of desired retention that minimizes the workload/acquired knowledge ratio.

Which in practice mean the following:

It's important to note that you can set your desired retention higher than recommended if you want to do more work (minutes of studying per day) to remember more, but you shouldn't set your desired retention lower than recommended because you would have to do more work to remember less.

In other words, setting minimal recommended retention too low is actively detrimental for studying efficiency. And there are a lot of anecdotal reports of recommended retention being within 80-85% interval for long-term knowledge acquisition, whereas default retention in 90%, meaning time is wasted for over-practice.

Only input required is "Days to simulate". Simulation code is here. This metric is essential for efficient studying and there is no easy way to export studying data to calculate in Anki either.