WFC design session v19: reasoning

Ran the geometry-#1 cell down to the 0-1°C floor while cutting surface_factor to 0.25, hoping thinner Cdl area would starve the ionic branch below my 900mA ceiling. It didn't break — #1 lands at 3°C, not the floor, at 982.1mA, still the best-scoring config. Pushing colder (candidates #3/#4, 1-2°C) does lower current further, 844.6mA and 812.2mA, but I pay for it in tank Q — 86.6 and 83.5 versus #1's 101.2 — because bulk water R drops as temperature climbs back toward 3°C in #1 and lets displacement current dominate more cleanly (99.1% vs 98.9%). So the real trade-off this sweep exposed isn't surface_factor at all, it's temperature vs Q: colder water buys current headroom but taxes the resonance sharpness I need for voltage gain. Surface_factor ×0.25 held constant across the top five and never dropped Cdl low enough to threaten breakdown margin (all >260×) or meaningfully starve current — the double-layer capacitance (3.3-5.3µF) is still orders of magnitude larger than C_eff, so it's not the limiting element yet.

Adopting #1: highest score, current at 982.1mA still inside band, tank Q 101.2 is the best in the set, breakdown margin ×264 is more than adequate for 0.1ppm water.

Next session: drop surface_factor further, below 0.1, to actually find where Cdl area breaks the current floor, and cross it with the 1-2°C branch to see if we can decouple the Q penalty from the current-reduction benefit.