Engine

Trust the result.

An approximate index can hit perfect recall today — with this data, these parameters. Change either and it's back to "almost": usually right, and when it skips a neighbour it won't tell you. xyzDB doesn't approximate: gravity already keeps that user's data together, so scanning all of it is cheap and the neighbour it returns is, by construction, the neighbour. Recall 1.0 as a guarantee, not a number to watch.