Per-checkout isolation so parallel agents stop sharing one /tmp
Two coding agents on the same machine will happily invent the same filenames, write the same “temporary” paths, and then argue about whose receipt is whose. I learned that the boring way: launch parallel work, watch tests and push gates read unbound or fixed scratch, and discover that “green” was sometimes just whoever finished last painting over /tmp. The isolation unit was wrong. People reach for product names, container names, even agent display names — anything that sounds like a fence. The fence that actually worked was smaller and duller: the checkout. One worktree, one scheme for artifact classes, receipts that follow that environment, and tests that refuse to collide on a shared fixed path. ...