The Agent Undo Button Is a Saga, Not a Stack
A user clicks "undo" on an agent action that fanned out to twelve tool calls. The agent sent two emails, created a calendar invite, updated a CRM record, charged a card, and posted to a Slack channel. Three of those operations are non-reversible by API. Two are reversible only by an inverse operation that fires its own downstream notification. The remaining seven each have their own definition of idempotency that the planner never reconciled. The undo button you shipped looks reassuring. It quietly succeeds about 60% of the time and silently fails the rest.
This is not a UX bug. It is a saga-pattern problem that distributed-systems engineers have been working on for thirty years, and ignoring that lineage is the most expensive way to discover it.
