@zwarich@hachyderm.io had you seen https://arxiv.org/pdf/2604.09961 yet? mlir has their "region" thing which lets you stuff a whole sub-CFG with references to the outer context into an operand, similar to ideas for "subfunctions" we had for SIL. a late pass to split out invocation functions for closures that survive inlining/DCE/etc. seems reasonable for ultimately targeting LLVM or WASM. but if you do pascal style nested funcs with chained activation records, you could probably lower that representation directly