Function instantiate 

pub fn instantiate(
    data: Rc<ModuleData>,
    frame: &[Value],
    ctx: &Ctx,
) -> Result<Value, Raised>

Instantiate a compiled module: build its Module terminal — the environment its item bodies run in — and hand it back as the Value::Module that is that terminal.

This is where a module gets an identity. The Rc is fresh per call, so two instantiations of the same ModuleData are distinct objects, and one instance is equal to itself across accesses. It is also where the module’s id block is reserved: one bump of the context’s id source covering every item, so materializing item i can stamp its closure with the stable id_base + i rather than a fresh id (see materialize_body and docs/done/2026-08-13_elly-modules-env.md).

frame supplies the module’s outer values, positionally, against the names ModuleData::frame_names recorded at compile time — the module’s import signature, filled in. A length mismatch raises .module_arity rather than going through: it is memory-safe (indices are checked) but silently wrong, so it is worth catching where the mistake is. A module with no frame takes an empty slice.

The values are copied into a flat Frame node, which is the shape a fixed slot list wants. The terminal’s frame is a plain Env, so a consumer that needs a cons chain instead — recur, whose frame is the enclosing lexical environment — builds the terminal directly rather than through here.