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.