fn formula_dsl(model: &Model, formula: &Formula) -> Option<String>Expand description
Render formula as symbolic-DSL source text that parser::parse_expr parses
back to the identical AST, or None when the v1 grammar has no exact
spelling for the shape (a bare ref carrying over/except, a
multi-category OVER, an empty measure/category name, an
enum/error/negative/exponent literal, an unknown function id). Callers fall
back to the controlled-English description for those, which
commit_formula also accepts.
Awkward names are no longer a refusal reason: ident quotes them
('Unit Price', 'Price/Unit', 'Over') per plan Step 4b.