A BONE (.bone.json) is a generator-agnostic prompt contract. It defines:
fields(plus UI hints)providerandtarget(image / video / audio / style / custom)attaches_toprompt_assembly(template / sequential / raw)- optional
output(render write-back) llm_instructions— a per-generator writing guide- routing / execution metadata
Swap generators by swapping the BONE — the story is untouched. BONEs install to templates/bones/. See also BONE inheritance and structured-frame bones.