· Workspace
Worktrees, a diff pane, and checkpoints
An environment split that gives a session its own worktree, a diff pane to review what it did, and checkpoints to undo it.
Two agents in one checkout edit each other's files. Giving a session its own Git worktree makes parallel work possible without either of them noticing the other.
The diff pane is where the result gets read. Diffs use colour plus signs, line structure and labels (colour alone never carries add or delete state), and they take the full useful width rather than a centred column.
A checkpoint taken before a long run is the thing that makes letting one loose reasonable. Restoring is itself undoable.