One feature, one file

Merge conflicts among parallel agents are a structural property, not bad luck. They concentrate in hub files: the files every feature must touch regardless of what the feature is. Measured over real agent-managed repos, the top conflict files are always the same shapes: the file holding every subcommand handler, the single integration-test main, the HTTP router, the monolithic agent doc. Change the structure and the conflict rate follows.

The rule

New behavior gets its own file. The shared file it plugs into grows by exactly one line.

One line means a mod declaration, a route registration, a match arm that delegates, a re-export, a table entry. The body (the handler, the scenario, the page, the logic) lives in the new file. Two agents each adding a file plus one registration line auto-merge almost every time; two agents each adding a 200-line function to the same file conflict almost every time.