G54 -- Port the banked sibling's spelling before touching a dial

When a same-family sibling is banked, its source spelling is ported with the target's constants before any lever is tried; a hand pass opens with a grep for the idiom's literal constants across the source and an objdump of each hit's window against the target. A similarity score is not a shape oracle. provenance: BFM R71 + R72; a same-shape sibling scored 0.55 after ~1M tokens of dial work