Preview pool matches

Runs a filter against the shared lead pool and returns the exact match count plus a small sample. Always run this before a build: the count it returns is the same number the build gates on, so it tells you in advance whether a build will be accepted and how many contacts it would create.

The filter is rejected outright if it is not selective enough to run quickly. The pool is over 100M rows, so an unbounded filter is not a slow query — it is one that must not start. A filter qualifies when it carries at least one of: v_category_in (preferred — verified from the company's own website), industry_exact, industry_pattern, p_bucket, sic_code_in, a keyword of 2+ characters, or state together with employees_min.

Geography is US-state-level. Use state (2-letter code) and city. There is no country filter — the pool has no country column, so passing one is rejected with a 400 rather than accepted and ignored.

A few filters the pool cannot honour (founded_year_min, founded_year_max, funding_stage_in, technology) are dropped rather than rejected. When that happens the response carries a warnings array naming them, so a count is never mistaken for a narrower one than it is.