Query-side filtering: a typed predicate tree over a point's JSON payload.
How a filter runs is chosen by the embeddable database's planner: when the
filter is selective on secondary-indexed fields it pre-filters to an exact
candidate scan, and otherwise it post-filters the vector-search candidates
(see quiver-embed and docs/index/design.md). Either way the [Filter]
tree is the stable wire shape and is re-checked on every surviving candidate,
so results are exact.
Field references are dot-paths into the payload object ("user.age").