Model eval as one call returning stream + future - #24
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`interface eval` drops its `evaluation` resource for a single synchronous
import: `eval(js, send: stream<string>) -> tuple<stream<string>,
future<result<string, error>>>`. The channels are component-model streams
and the completion a future, so every lifetime question now has the
CABI's answer: "no more values" is the stream closing, "already
completed" cannot be asked twice of a future, and a fire-and-forget eval
is a dropped reader the host's eventual write sees as `dropped`. The
`finished` error case goes away with them.
This also removes the macrotask deferral the host carried against
polyengine#280. Measured on the same build and click path: a subtask
import settling in the microtask checkpoint after `handle-event`'s
initial activation returns is lost, while a future-typed import settling
at the same moment (even from an already-resolved promise) is delivered.
Future and stream writes take a different path through the runtime than
subtask settlement, so the shape sidesteps the bug rather than papering
over it.
Guest: `Evaluator::send` is synchronous and at most one write may be in
flight per stream end, so sends stage into a `Vec` drained by a spawned
task that owns the writer for the drain (the renderer's own
`stream`/`pending` pattern). The `recv` reader is moved out of its slot
for each await and put back. Owner-lifetime handling is unchanged.
Host: returns `[AsyncIterable, Promise]` synchronously; the runtime lowers
both ("Lowering accepts the natural JS producers"). The stream is closed
before the future resolves so a reader never observes completion with a
value still in flight. Fixture and end-to-end tests are unchanged.
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Follow-up to #23.
interface evalbecomes a single sync import:eval: func(js: string, send: stream<string>) -> tuple<stream<string>, future<result<string, error>>>; variant error { invalid-js(string), communication(string) }Why: the CABI now owns every lifetime question (stream close = no more values; a future is read once; fire-and-forget = dropped reader), so the
finishederror case and the resource are gone. And it removes the macrotask workaround for polyengine#280: measured on the same build, a subtask import settling right afterhandle-event's initial activation is lost, while a future-typed import settling at the same moment is delivered (comment on #280 has the matrix).Guest (
src/document.rs): sends stage into aVecdrained by a spawned writer-owning task (one in-flight write per end); the recv reader is moved out of its slot per await. Owner-lifetime scheme unchanged.Host (
host/src/eval.ts): returns[AsyncIterable, Promise]synchronously, lowered by the runtime; stream closes before the future resolves. No deferral anywhere.Fixture and
eval_component_test.tsunchanged and green; unit tests rewritten for the new API. Fulljust check/fixtures/example counter/testpass.Automerge armed (merge commit).