Retire the flat-JSONL retry rung. Every subagent rung now emits a JS
program (script-gen); reduced_complexity and minimal_skills only
narrow the loaded skill set — they no longer switch the output format
to positional _parent JSONL, whose omittable parent field collapsed a
whole tree into flat siblings when a model skipped it. script-gen's
I(parent, node) makes parenting a positional argument that cannot be
dropped, and the reasoning-harvest fix made it robust across models.
parse_nodes stays for the modify/chat paths that still consume flat
node JSON; the jsonl-format generation skills are removed.
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