EX-13 · Route α by query class

Difficulty: 🔴 · label difficulty: 3 Stuck? Ask in the clinic thread for EX-13 — one long-running thread per exercise, so the answers accumulate where the next person will look. Submit: post it in Show and Tell titled [solution · EX-13] ..., with your numbers and your interval.

Notebook 04 · ~2 h · Seam ④ · Skill: the honest next step after a global α

Notebook 04 finds a single global α is a compromise. Build a router that picks α per query class and measure whether routing beats the best global value.

Acceptance criteria

• The router (text-only features — no gold labels)
• Router precision/recall reported as its own metric
• Routed vs best-global, with an interval, on dev and on frozen
• A statement on whether the second system is worth its own maintenance

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