Simulated-annealing acceptance: accept a move with energy change delta at temperature
with probability 1 if improving (delta <= 0), else exp(-delta/T). rand01 ∈ [0,1).
One CPU step of gradient-based belief diffusion (discrete graph Laplacian): each node’s
belief moves toward its neighbours’ average by rate ∈ [0,1]. edges are undirected (i,j)
index pairs. Writes the updated beliefs into out. Zero-heap (caller buffers, no allocation).
Trigger a diffusion pass for the named graph. Returns true if enqueued,
false if the graph_id is empty (no-op). The actual GPU pass runs async
via execute_diffusion_pass; this function is a synchronous CLI entry-point.