spec/coroutines.sx: define-library with make-coroutine, coroutine-resume,
coroutine-yield, coroutine?, coroutine-alive?. Built on existing perform/
cek-step-loop/cek-resume suspension machinery.
spec/tests/test-coroutines.sx: 17 tests — multi-yield, final return,
arg passthrough, alive? predicate, nested coroutines, recursive iteration,
independent coroutine interleaving.
Key: coroutine body must use (define loop (fn…)) not named let — named let
transpiles to cek_call→cek_run which rejects IO suspension. All 17/17 pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
giles
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