Typo repair is the one rung whose cost tracks the vocabulary rather than the
result, and it only runs for a term the scope has no posting for. Measured over
1.6 M distinct terms: 10 ms for one unknown term, 387 ms for a 480-character
query of thirty-nine of them.
The scoped-count fix made that cheaper rather than dearer, from 737 ms, because
ordering the vocabulary scan by term drops the sort `doc DESC` needed and the
counts it adds are at most eight bounded probes per prefix. A cap on unknown
terms per query is a follow-up in the split plan, with the five other items the
final review raised and did not route.
Jinwoo-H
a5d178b9af