When a Turbopuffer query returns empty unexpectedly, check the namespace schema first: every attribute you filter on must have filterable set to true. FTS, regex, glob, and fuzzy attributes default to non-filterable, so declare filterable explicitly for any attribute you plan to filter. Audit the schema with ns.schema() before debugging the data.

Context: Official Turbopuffer skills repo (doctor reference): documents the gotcha that filters on non-filterable attributes silently return empty results. There is no error, the query just comes back with nothing, which makes agents chase phantom data problems when the real issue is the schema.