A Concrete 'Zones' Model for Running Coding Agents Safely in Legacy Codebases

Addy Osmani's field guide to brownfield agentic engineering: a green/yellow/red risk-zone map (a human draws it, never the agent), durable 'comprehension memo' research artifacts so agents don't repeat archaeology, turning repeated corrections into harness rules instead of one-off diff fixes, and a 'parallelize last' principle backed by data showing only 28 of 520 agent migration runs passed full audit.