realized_vol_21d

Annualised stdev of the trailing 21 session returns. COMPUTED BACKWARD, unlike UW's /volatility/realized which computes it FORWARD over ~20 sessions and is therefore not knowable on the date it is stamped with (DESIGN.md:139, the highest-priority provenance hazard in the document).

The cross-section of every symbol at 2026-09-18 was stopped by its statement timeout. The XLV figures above are unaffected.