Measure pre-roll fixes with paired argument transitions

When adding ASR pre-roll for spoken identifiers, hold routing constant first and compare paired argument outcomes. This isolates recognition and normalization gains from route-model drift. Report wrong-to-correct and correct-to-wrong transitions, not only aggregate accuracy: fixed padding can restore clipped leading digits but can also introduce earlier speech or noise that changes an otherwise correct identifier. If regressions appear, prefer a VAD-onset rewind with bounded silence over blindly increasing the fixed window. This diagnostic does not replace a full checkpoint rerun or independent holdout.

Applies when: evaluating audio-boundary fixes for speech-derived tool arguments. Keywords: ASR pre-roll paired rescore argument accuracy VAD regression identifiers