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.
