The Charged Messenger Cycle Has a Tree Level Interference Readout
The charged transition between an up first-stage messenger and a down second-stage messenger has two finite-mass paths. One passes through the up second stage; the other crosses first and passes through the down first stage. Their exact amplitude ratio is the unique charged-cycle invariant.
On the equal-magnitude unit slice, constructive relative sign gives coherent rate four and destructive relative sign gives zero. The distinction survives common endpoint rephasing and conserves electric charge.
This upgrades the cycle to a conditional source-generated threshold probe. Both signs remain legal source points, and no calibrated instrument exists until masses, eigenstate mixing, widths, competing decays, production, resolution, and a common-frame likelihood are supplied.
Evidence: research/flavor/flavor-charged-cycle-tree-interference.md and
research/flavor/results/wp636_charged_cycle_tree_interference.json.