**Figure S — Dynamic neutral projection repairs the multiplicative
mixed-traffic failure.** **a,** Training-only batch losses for the frozen D1
dynamic controller and the earlier closed-form/frozen-predictor controller
lesion. The lesion curve is a labeled pre-grid diagnostic rather than a
preregistered endpoint; it visualizes the failure that motivated D1. Both
records use the same ResNet-20 family, four-to-one soma-coupled traffic,
momentum, learning rate, and 352-step boundary. **b,** Before each D1 update,
the neutral residual remaining after the slow predictor grows with the task
state. A fast affine projection based only on paired instruction-off local
soma/apical observations holds the post-projection residual below
`3.03e-8` of traffic RMS. The fast coefficient fit observes no task
instruction and leaves the slow predictor frozen. **c,** The separately
frozen 20-epoch D2 endpoint reaches `83.58%` validation accuracy, versus
`82.66%` for clean reciprocal KP and `10%` for each raw, norm-matched, and
original frozen-innovation MT-1 condition. The MT-1 bars do not receive the
new controller and are retained as historical failed controls. D2 uses one
seed, one final validation evaluation, zero test evaluations, zero task-loss
queries, and `1.326x` the matched BP affine-MAC estimate; the paired neutral
microphase and 4.070e12 elementwise operations are reported separately.