The daily 40%-off coupon was being merged into every trucking/UCR/IFTA/OTC
send, but those discount sends were not actually being delivered (the
DKIM-broken window). Now that deliverability is fixed, re-test whether
normal-price offers convert before giving margin away.
New CAMPAIGN_ENABLE_COUPON env flag (default OFF) gates daily-coupon
minting in build_trucking_campaigns + the UCR/IFTA/OTC builders (which
import it as tc.COUPON_ENABLED). With it off, no code is minted and an
empty coupon_code is merged -> the campaign templates' existing
{{ if .Subscriber.Attribs.coupon_code }} guard falls through to the
normal-price {{ else }} branch and landing-page links carry no ?code=.
No template or DB changes; fully reversible (set CAMPAIGN_ENABLE_COUPON=1).
Verified: COUPON_ENABLED defaults False, coupon_attribs(None) -> empty,
lp_link drops ?code= when no coupon, all 4 builders compile.