fix(preview2-shim): throw invalid would-block from browser incoming-body read - #2043
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`wasi:io/streams` stream-error only has `closed` and `last-operation-failed`
variants - there's no `would-block`. The browser IncomingBody's non-blocking
read() threw `{ tag: "would-block" }` whenever no data was buffered yet, which
JSPI-driven callers (e.g. wstd's Reactor loop) can't lower into a valid
stream-error, silently swallowing the failure and hanging forever instead of
surfacing an error. Return an empty array instead, per spec, and let the
existing subscribe()/wait mechanism handle backpressure like it already does
for blockingRead().
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Fixes #2042.
wasi:io/streamsstream-error only hasclosedandlast-operation-failedvariants - there's nowould-block. The browser IncomingBody's non-blocking read() threw{ tag: "would-block" }whenever no data was buffered yet, which JSPI-driven callers (e.g. wstd's Reactor loop) can't lower into a valid stream-error, silently swallowing the failure and hanging forever instead of surfacing an error. Return an empty array instead, per spec, and let the existing subscribe()/wait mechanism handle backpressure like it already does for blockingRead().