Join in week six with week six's machine

The course container is a timeline. Every Friday the instructor snapshots it: week-1, week-2, up to week-12. Each one holds the packages installed that week, the starter code, the database seeded for that week's lab.

A student transfers in during week six. Their container is copied from the week-6 snapshot. They don't reconstruct five weeks of setup from a README nobody updated; they open the terminal and the machine is exactly where the class is.

A student who fell behind and broke everything in week nine restores their own week-8 snapshot and loses one week instead of a semester. A student who wants to revisit week three opens a copy of it next to their current work.

The syllabus has a snapshot for every week, and a student can stand in any of them.