Draw the map before the agents start

Osmani's premise is that in an old system "the repository is no longer a complete description of how the thing actually behaves", and that agents make a change cheap to attempt without making it cheap to verify. His answer is to zone the codebase: green for well-tested, isolated, modern code where agents run in a tight loop; yellow for mixed quality, where characterization tests get written first; red for authentication, billing, permissions and payroll, where a human pairs on every step or the work does not happen. Three rules turn that from a metaphor into a procedure. A person draws the map, because an agent left to choose "starts in the scariest file, because the scariest file has the most interesting names". A zone only moves when the move is earned, meaning characterization tests exist and the module owner has reviewed the agent's first changes. And the zone decides the verbs. Three further rules sit on the same reasoning. Autonomy should track blast radius and recoverability, not model confidence, because "a model's confidence is a poor guide". The session that makes the tests pass should not also be the session that wrote them. And a migration is finished only when the old path is gone, since "if deletion is a future cleanup ticket, the migration unit is not complete". He cites SWE Refactor Bench for the cost of getting that last one wrong: across 520 agent runs, 28 passed its migration audit, behavioral tests and independent verification.

Why it matters: the harness literature is largely written for repositories that were designed for it. Zoning is a way to get an unattended loop running in the part of the codebase that can absorb one, without pretending the rest is ready. The rule that will earn its keep soonest is the smallest: pin today's behavior in a separate pass, by a person or a different session, before an agent starts changing it. A green suite an agent authored to pass its own work is not evidence.