Four Coding Agents Need Four Workspaces, Not Four Chat Windows

Opening four coding-agent sessions feels like scaling. On a shared machine, it is closer to giving four fast contributors the same repository, shell, credentials, ports, caches, and merge queue without deciding who owns any of them. The first failure probably will not come from model quality. One task will restart a dev server while another is testing it. Two workers will touch the same lockfile. A branch will pass its own checks and still conflict with a migration waiting in the merge queue. Four chat windows create concurrency. Four owned workspaces plus one deliberate merge queue create a system. Parallelism multiplies shared state Tasks that sound independent in a prompt can overlap in the environment. A frontend change and an API change may both edit generated types. Two test runs may expect the same database or browser profile. Separate worktrees can still launch services on the same port, read the same environment variables, and write to shared caches. The agents do not collide in the prompt. They collide in everything the prompt lets them touch. This is why adding a second agent changes the job. With one worker, the operator can keep a surprising amount of state in their head. With four, every unstated assumption becomes a race condition or a review problem. The fix is to make ownership visible before execution starts. A worktree is the start, not the boundary Git worktrees are a sensible first step. Each task gets its own branch and working files, so one agent is less likely to overwrite another agent's edits by accident. That is useful isolation, but it is narrow isolation. A worktree does not reserve a port. It does not separate process trees, temporary directories, credentials, network access, browser state, or external services. Treating it as a sandbox gives the workflow more confidence than the boundary deserves. Proliferate is an instructive project example because its documented design pairs isolated task worktrees with visible review state. The imp