Janet fibers are stackful coroutines, so a go block is just its body run in a
fiber that parks on channel ops by yielding to the event loop — the interpreter
call stack rides along, no CPS/state-machine transform. So <!/>! work anywhere
(inside try, nested fns, loops), unlike Clojure's go macro.
src/jolt/async.janet implements chan/chan?/close!/<!/>!/<!!/>!!/go/go-loop/
thread/alts!/timeout/put!/take! over ev/ channels and fibers, installed as the
clojure.core.async namespace (pre-populated in init, so require finds it).
A channel is a pair of ev/chans (:ch values + :done close-signal); a take is
(ev/select :ch :done), which drains buffered values before the close signal —
giving Clojure's drain-then-nil semantics without the buffer loss of
ev/chan-close, and with no leaked fibers (close! just closes :done).
Single-threaded cooperative scheduling: <! (park) and <!! (block) coincide.
Dynamic-var conveyance (Phase 2) and channel transducers (Phase 3) are TODO.
spec: test/spec/core-async-spec (16 cases — go/channels, buffering+close,
go-loop pipelines, alts!/timeout, parking inside try/nested-fn). jpm test green.
