packfile.h: pf_load refuses a generator other than 2 or 3 (spec 01 section 1.4.5), reads IGNEUM_PROGRAM_CLASS
(must match the generator) and IGNEUM_ERA_SEED_HEX; pf_pack_class_ok and pf_class_token are the one rule for
the `class=<v2|v3> era=<hex>` tokens a job or prepare line of a class v3 epoch ends with (a v2 line is the
line of before, byte for byte). CUDA worker.cpp and OpenCL host.c: a pair's identity includes its class and era
when the line names them, so a prepared pack of the right class wins over the resident pack of the same seeds;
right seeds with the wrong class answer `need` plus `error <id> pack <dir>: program class mismatch ...`, and a
prepare on a pack of the wrong class fails in plain words. Metal main.swift: refuses every class v3 line until
the Swift generator carries version 3 (the integration branch). emu/packfile-test.c: the generator rule, a v3
pack with its era, the token matcher, the contradicting class line (13 checks pass).
igneum-pow verify.rs: Epoch::chain_dataset(day, class), the one entry the node's day cache goes through, so the
ca2-mixer class-specific item construction and cache schedule have a seam.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>