The full rate stack (federal + NIIT + state) was used for the recorded
tax columns and for realized gains at rebalances, but the equity path
itself deducted only the FEDERAL rate in two places:
1. distribution reinvestment kept (1 - div_rate)/(1 - lt_rate) instead of
(1 - div_rate - niit - sl_rate);
2. the per-date liquidation tax ('sell everything today') passed bare
(lt_rate, st_rate) to _liquidation_tax.
Symptom: FLCSX 10Y showed a 1.4pt after-tax drag instead of the true
~2.8pt. Fix: d_keep/c_keep factors and stacked liquidation rates.
Regression tests pin the equity path: reinvested net with NIIT+state,
ST and LT liquidation tax at the full stack (all fail on the old code).
Corrected 2015-2026 NYC after-tax: SPY 13.82->11.23, IVV 13.81->11.22,
JLPSX 13.68->9.18 (previously reported 12.51/12.50/11.31, superseded).
Greg Pomerantz
9f657dc9f4