Plasmid-loss: f(n)=exp(−λn); n_half=log(2)/λ; at λ=ln2 → n_half=1; retained@2gen = 1/4

Sympy-exact symbolic witness of plasmid-loss exponential decay canonical form and generation-half-loss anchors. Setup: P_0, λ, t, n — all positive symbols. Time-continuous decay: P(t) = P_0·exp(−λ·t) (sympy canonical 'P0*exp(-lam*t)'). …