Foremerge: Open-Source Tool Prevents Silent Conflicts Between Parallel AI Coding Agents

Developers building GPTree encountered a silent but critical failure when multiple AI coding agents — Claude Code, Codex, and Cursor — worked simultaneously on the same repository, producing clean Git merges that nonetheless broke the codebase at a design level. The core problem was that Git compares file diffs, not agent intentions, leaving three failure modes unresolved: destructive versus additive changes, duplicate work, and contract drift. To address this, the team built and open-sourced Foremerge, a coordination protocol that sits above Git and requires agents to declare their intended changes — including semantic scope and operation type — before executing them. When two agents declare overlapping scopes, deterministic rules compare the declarations and surface a conflict warning while both tasks are still in the planning stage. Foremerge uses advisory leases rather than hard locks, ensuring agents are warned and given shared context without being blocked from proceeding.