Phase D8 compute was returning x_fc_margin_percent already-multiplied
by 100, but the 'percentage' widget in the SO form multiplies again
for display. Result was 10000% instead of 100%.
Store as 0.0-1.0 fraction; widget handles the multiplier. Caught
during UAT on S00066.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>