Linters that teach

Ablation lab (Module 14, L14.3, interview checkpoint): a linter teaches when the message at the error carries what, why, the exact fix, and the principle. A cryptic cascade of E302, E501 and W504 takes 12 turns and learns 0 principles. The line that trips E501 is 87 characters against a 79 limit, 8 over. The teaching E302 message takes 1 turn and the next file has 0 violations. A clean file exits 0. Across the same 10 tasks, teaching mean turns are 0.5 with 5/5 repeats avoided, and cryptic mean turns are 4.0 with 0/5. Fix rate is 10/10 on both, so the gap is not the exit code. The agent is a script. The rule codes are the published pycodestyle names. Seed 0, no model call.

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