-- A function or builtin name used as a value yields a FnRef on every
-- engine. Pre-fix this only worked on the tree interpreter; the VM and
-- Cranelift JIT lossily encoded the name as a `"<fn:name>"` heap string,
-- breaking any program that round-tripped a function-as-value through a
-- register. PR 1 of the HOF-dispatch effort tags FnRefs as a non-singleton
-- QNAN payload so the value flows losslessly across all engines.
--
-- This example pins the contract: a function returned, bound, and then
-- returned again still renders as `<fn:name>` end to end.
-- A trivial user function, used purely as the target of FnRef plumbing.
sq x:n>n;*x x
-- Return a user function by name.
mku>F n n;sq
-- Return a builtin by name. Pure builtins are verifier-promoted to a
-- function type so the bare `abs` ref slots into `F n n` cleanly.
mkb>F n n;abs
-- FnRef survives a local binding before reaching the return slot.
bnd>F n n;f=sq;f
-- run: mku
-- out: <fn:sq>
-- run: mkb
-- out: <fn:abs>
-- run: bnd
-- out: <fn:sq>