`stats count by host` with no leading filter is documented as valid in
/docs/query-language-reference.md, but every pipe-stage keyword is also
a valid bare identifier, so the parser read it as a base_search of four
ANDed free-text terms ("stats", "count", "by", "host") -- matching
nothing, and returning an empty result rather than an error, which is
the worst of both outcomes for anyone typing it.
Recognizing a leading stage keyword up front and skipping straight to
stage-parsing fixes it with no planner or executor change: q.Base stays
its zero value, and compileBoolExpr already treats zero terms as
match-everything. The comparator lookahead keeps a genuine field named
`where`/`stats` (`where=foo`) parsing as a filter, as before.
jcoffey-dev
754996dbfd