Many teams are starting to use more than one AI coding agent. One agent writes code. Another agent reviews. A human owner makes the final call. That sounds reasonable, but without a shared process it can become unreliable very quickly. The Executor may test its own work. The Reviewer may only check that tests are green. The Owner may receive a confident summary without durable evidence. That is the problem ACS tries to solve. ACS, short for Agent Collaboration SOP, is a vendor-neutral, file-first workflow for multi-agent engineering collaboration. The core principle is: Green tests are evidence, not approval. Passing tests matter. But they do not prove that scope was respected, UI was inspected, docs match the actual files, public output was redacted, or the change is safe to release. Why Green Tests Are Not Enough Tests answer specific questions. Approval answers a broader question: should this change move forward?…