Long-running automated work usually persists its position as a stage name. That is enough to describe where the work got to, and not enough to describe what it was doing. When a single stage can stand for more than one pending operation, a crash in the wrong moment leaves you holding a label instead...

When several different code paths write to the same shared invariant, making one of them safe in isolation does almost nothing. The invariant is only as protected as its least careful writer — and "atomic" means very little if each writer is atomic in its own separate way.

The problem

We had a sha...