The subtask prompt contradicted itself: the jsonl-format skill taught
flat `_parent` while NODE_FORMAT (appended last, so dominant) demanded
a JSON array with nested `children`. Weaker models followed the last
instruction and emitted flat, unnested nodes, collapsing every layout
to a vertical stack. Align NODE_FORMAT and the basic-tier simplified
skill (both Rust + TS copies of the corpus) to flat `_parent`, and make
the user-prompt format line format-agnostic so it conflicts with neither
tier's skill.
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