The previous articles built up a picture of what a compiler can verify about individual operations: their outcomes, what data they can see, what state they require. The operations article introduced N-track pipelines where every outcome gets handled and errors can accumulate along the way. If every step is a pure transformation, that model is sufficient — errors collect, the caller handles them, nothing external has changed.
But real procedures aren't pure transformations. An away mission involves assembling the team, briefing them, beaming them down, establishing contact, collecting samples, and beaming them back. Each step commits real effects — crew assignments change, transporter logs update, communication channels open. When step four fails, steps one through three have already happened. Accumulated errors tell you what went wrong. They don't undo what already happened.
I explored error recovery for effectful pipelines — steps that commit external state, not just transform data. The answer was compensation: each forward step paired, when possible, with the action that reverses or settles it. Ruuk's saga keyword makes that pairing a first-class part of the declaration.
The Problem: Distributed Commitment
