Run 2's reasoning battery reported zero truncations and zero degenerates on both
arms across four passes. The same tune, measured on long-form generation in the
same session: truncated 0/384 -> 38/384, degenerate 0/384 -> 19/384. A real
output-stability regression, structurally invisible to that gate because its
answers are short.
Not a bug in the battery -- a coverage property. An instrument measures the
regime it samples, and output length is a regime. Generalises to context length,
conversation depth, and any axis where the gate's operating point is narrower
than production's.
The actionable form: enumerate the regimes your gate set spans, name the ones it
does not, and decide deliberately rather than discovering the gap downstream.
Corollary on sequencing -- put a long-form generation in the gate and put it
early, because a length-dependent regression is exactly the one you want found
before four clean short-task passes make everyone comfortable.
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