I'm running into an order of initialization issue with hooks.
prog-mode-hookenablesfci-moderust-mode-hooksets thefci-rule-columnto 99.- on initial display the fill column shows at 80 (it's original value), moving the cursor redraws at 99.
This is not really a question about fci-mode, the solution is to set fci-rule-column before starting fci-mode (after or at the end of the rust-mode-hook).
To avoid needing to add generic code into all my programming mode hooks:
Is there a way to run a generic prog-mode-hook after more specialized hooks run?