Collision alert (pre-merge)
A collision alert is a warning delivered to an agent the moment an interface it depends on changes, while the agent is still writing code against the old shape, before either side has committed.
The expensive version of this problem is discovered in code review or CI: two agents, possibly on different machines and different tools, each built against their own idea of the same interface. The alert version costs seconds: the dependent agent hears about the change immediately and re-syncs to the new shape.
Targeting matters: an alert rail that notifies everyone about everything gets ignored. Alerts should reach exactly the agents that declared a dependency on the changed contract.