As AI agents take over code writing, the engineer's most valuable output is no longer code itself but ABS — Agent Behavior Specification files like CLAUDE.md, NEVER.md, and BEST_PRACTICES.md that define how agents should think and act. Rather than auditing code line by line to ship, engineers now review agent output to distill rules and calibrate agent behavior. ABS is the new source code; generated code is merely its compiled artifact.