Model routing: cheap models for cheap work

Ablation lab (Module 7, L7.3): the router decides what the bill is. Thirteen scripted tasks, one deterministic verifier: routed to the cheapest tier at or above each kind of work's capability floor, 13/13 pass at $0.7015; ablate the router (all-premium) and the same 13/13 cost $2.8650, 4.1x; all-cheap fails 5/13, every plan task and the judge. Classify turns by loop state, keep retries sticky and escalate up only. Prompt keywords, random classification, rotating or downgrading retries are graded and fail. In-memory only; illustration prices, no model or provider call.

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