Git worktrees let multiple working trees be checked out from a single repository at the same time. Fleet uses this to give each agent its own isolated working directory on a separate branch, so several agents can develop concurrently without touching each other's files or stashing changes.
When an agent is configured with a worktree, Fleet places it in its own directory and the agent does its work there, opens a PR, and moves on. Worktrees share the main repo's git history and object store, so they are lightweight compared to full clones. This is what makes true parallel development with multiple AI agents practical.