PACT ContextLease

AI coding agents can work in parallel on the same project, but their plans can silently become outdated when another agent changes a shared API or dependency. PACT ContextLease is a proof-of-concept coordination layer designed to stop that stale context from turning into an unsafe write. In the demo, Backend owns the API contract and changes /api/login to /api/session. Frontend still depends on the old contract version, so PACT immediately marks its lease STALE. When Frontend tries to write, the registry checks both lease status and the live dependency version before any side effect occurs, and blocks the write with a typed PactStaleError. An unrelated Data Model agent continues normally because its dependency was not changed. Recovery is explicit: Frontend must acknowledge contract v2 and then receives a new lease ID. The old lease remains STALE permanently; the new lease becomes ACTIVE and the write succeeds. The target users are teams building multi-agent coding workflows, agent orchestration systems, or AI-assisted development platforms where several agents may modify a shared codebase or service contract in parallel. What makes PACT different is that it does not merely provide context or test code after the fact. It treats context validity as a versioned runtime condition and enforces it at write time. The prototype is deterministic, built with React and TypeScript, passes 18 automated tests, and is available as a public live demo. It simulates parallel coding agents and does not claim direct runtime integration with IBM Bob.