Explicit Seams as Agent Affordances

The agent’s diff was clean. Three files, all tests green, nothing obviously wrong in the PR. The problem was one of those three files: a service class with no interface in front of it, called from six places, and the agent had quietly changed the semantics of a method in a way that broke a workflow nobody had a test for. The agent didn’t know the workflow existed. The codebase didn’t tell it. The agent saw a function, read its body, and rewrote it. A week later I rewrote the same code with a port in front o