Operates on Vendors. In the Zuper client app this module is labeled "Vendor" for most companies, and "Supplier" for companies in the roofing industry — the API and data shape are identical either way. Vendors and Subcontractors share the exact same underlying schema and endpoints; they're distinguished only by the vendor_type field (VENDOR here) and the /vendors vs /subcontractors route prefix. Rule-engine-based list endpoint — an alternative to the simple filter.* query params on the plain List endpoint, for building complex AND/OR filter conditions.