module_ m rewrites each function body, folding the try_table-plus-block-ladder shape — a join block wrapping one parameterless block per catch clause, the try_table innermost with its value escaping to the join, and each handler's code trailing its block — into the structured try { … } catch { tag => { … } … } whose arms are honest fall-through code. The join label is kept as the try's label only when the bodies still branch to it. Ladders that do not conform (a targeted arm label, out-of-order clauses, a mid-list catch-all, …) are left as-is, decompiling to the bracket form instead.

Folding is the exact inverse of Ast_utils.lower_trycatch, so re-lowering reproduces the original blocks and the rewrite preserves runtime semantics. Meant to run on From_wasm.module_ output before Sink_let.module_ (which would otherwise sink locals into the ladder blocks and hide the shape).