Ines Park
Co-founder, Engineering
Why we made decision_log append-only.
A mutable log is a story you can rewrite. An append-only log is a witness you can call. We built Magistry on the second model — every action the agents take is a row, every row is signed, and no row is ever updated in place.
The first thing this buys you is provenance. When the Head of Paid Media asks 'why did we scale that ad?', the answer isn't 'the agent thought it was a winner' — it's a row, with the judge score, the evidence rows it pointed to, the executor that wrote it, and the operator who held the kill switch at that moment.
The second thing it buys you is reversibility. Every action is paired with its rollback op at the moment the action lands. Not computed later, not derived — written. To reverse: read the row, run the op. The agent doesn't need to remember anything.
Mutable logs are also where audits go to die. Tier-A cost confidence at decision time is not the same as Tier-A at read time. Append-only means the tier is stamped on the row when the decision was made — what the agent saw is what the auditor sees.