This skill should be used when the user says "batch implement", "implement all", "batch execution", "implement all features", "parallel implement", "implement in parallel", "arness batch implement", "arn-code-batch-implement", "run batch implementation", "implement everything", "launch batch workers", or wants to spawn parallel worktree-isolated background agents to implement multiple pending features simultaneously. Each worker runs as a full independent session with all tools. This skill requires pending plans in .arness/plans/ — run arn-code-batch-planning first if none exist.