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tt22 removed the formula crate's serde dependency with the legacy JSON loader, keeping serde only where a type crosses the wire. FormulaId crosses the wire, so it is the third such type. No derive goes back on the formula AST. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze