Running Claude Code in 4 Parallel Sessions Led to 'Team Development' — 7 Recipes to Prevent Collisions

📝 Originally published (in Japanese) at forge.workstyle.tech . In a previous article , we introduced an environment for parallel execution of coding agents using Git worktrees. This article is a follow-up. As we progressed with parallelization, we ended up with 3-5 Claude Code sessions simultaneously developing the same microservices . What happened was no longer just "parallel execution of tools" but actual "team development" . All the issues that arise in human teams—miscommunication, deployment conflicts, and territorial overlaps—occur here as well. And the practices that work for human teams work almost identically here. We’ll share seven recipes that emerged from actual operations, along with real-life close calls. Real-Life Story: Averting a Deployment Rollback Disaster at the Last Minute One day, while Session A (responsible for voice functionality) was in the middle of a major refactor, Session B (responsible for streaming functionality) sent this message: "We’re about to build the frontend as version 1.0.399 (based on main)." At first glance, this seemed fine. However, in this repository, the authoritative branch for the production environment was not main but a dedicated deployment branch . The latest features from the past few dozen versions were only in the deployment branch, while main was outdated. If Session B had deployed an image based on main, weeks’ worth of features would have been rolled back in production . Session A immediately sent a warning, and Session B halted the build before pushing. Session B then cherry-picked their changes into the deployment branch and rebuilt the image, avoiding the disaster entirely. All this communication was handled autonomously between the agents via session-to-session messages . I (the human) only learned about it later from the logs. This incident highlights two things: parallel agents can cause the same accidents as human teams , and with proper communication channels and rules, they can prevent accidents jus