I spent a year building a 300k‑line production platform alone using AI‑assisted engineering. It worked — but only when AI was cheap and predictable. As model behavior shifted and costs rose, the entire system began to break in ways most teams haven’t experienced yet.

This essay is a field report from operating at the edge: • how deterministic workflows collapse under model churn • why reasoning‑first models break text‑pattern assumptions • why AI engineering economics now resemble aviation, not cloud • what architecture survives when the foundation keeps moving

If you’re building AI‑native systems, this is a look at the failure modes that are coming for everyone.