Resolve: tau PTM barcode controls seed-competent trans-synaptic templating

Bounty tier: $750K biochemical plus circuit validation. This challenge requires isolating PTM combinations rather than treating total phospho-tau as one signal. Falsifiable prediction: tau fibrils carrying the pS202/pT205 + acetyl-K280 + D421 truncation barcode will produce >=3x higher recipient-neuron FRET biosensor seeding after microfluidic axon-to-soma transfer than matched fibrils lacking acetyl-K280 or D421 truncation. Enzymatic or CRISPR perturbation that removes one barcode component should cut propagation by >=50% without reducing total transferred tau by >20%.