Code review without the local checkout

A teammate pings you a PR. You open the review URL. A VS Code instance loads with the branch already checked out, dependencies installed, the dev server already running. You hit run. You watch the test fail. You set a breakpoint.

There was no git fetch, no npm install, no waiting for your laptop to catch up. The container was provisioned from a snapshot of the base branch and the diff was applied before you opened the URL. The state is real, not a sandbox approximation.

You leave a comment, close the tab, and the container goes idle. Tomorrow's reviewer opens the same URL: still there, still warm: an idle container burns no CPU and its cloned disk blocks are shared, so keeping it costs next to nothing.

Code review stops being a reading exercise and becomes a running one.

You review code on the codebase, not on a diff view of it.