Agents generally are stochastic.

Every time might be different.

That could be good if the situation also changes, or there's room for a positive surprise.

But if the situation is relatively fixed and with no room for more quality, and you have something that works right now, then it changing is bad.

Any change is downside.

Mechanistic software is deterministic and cheap.

If you wrap it in an agentic harness loop to re-heal it if it breaks, you get the best of both worlds.