Executable FPM: Reference Runtime, Numerical Contract, and Reproducible Audit

This paper specifies the public Python reference implementation of Finite Possibility Mechanics. The runtime executes the FPM master chain on a periodic 5×5×5 cubic lattice: 125 nodes, six nearest neighbours per node, and 400 ordered ticks in the standard production audit. Each node carries stored energy, a directed 3×3 route ledger, a nine-channel complex carrier, viscosity, prior, cache bias, and derived observables. Ordinary action is replenished through the local reversible kernel proved in Paper 1; capacity overflow, starvation, Landauer debit, and explicit torsion-link operations are recorded in separate signed accounts. The implementation reproduces the exact algebraic identities to floating-point precision. The standard master run closes the expanded ledger while exercising capacity routing, starvation, information erasure, finite microcell quantization, and linked torsion quantization. These are reproducible implementation checks of the stated equations, not independent physical evidence.