ETF flows: issuer primary-source check + public JSON API
The US spot ETF tracker now reads BlackRock's own IBIT page every day (shares outstanding, NAV, net assets) as a source independent of the flow tape: shares × NAV is checked against the tape's net assets and the day-over-day change becomes an issuer-implied flow. The series ships as the free etf-issuer-daily dataset on /data, and the whole product finally has a JSON twin at /api/public/etf.