Play as Voluntary Displacement Practice: Safe Departure from S⁰, Return Path Learning, and the Evolutionary Function of Non-Serious D(ξ)

Play is voluntary, safe exploration of displacement from ground state — specifically to learn the return path before stakes are real. The play frame licenses D(ξ) exploration without real Φ accumulation. Flow is optimal D(ξ_play) calibration. Humor is rapid cognitive displacement and return. Play deprivation limits the return-path repertoire, increasing vulnerability to real displacement.