Enum OutputSink 

pub enum OutputSink {
    Stdout,
    Capture(String),
}

Where write/1/writeln/1/nl/0 send their bytes. The CLI/WASI shell streams to process stdout (the v1 contract); the Tier-2 reactor has no stdout in a V8 isolate, so it captures losslessly into a buffer that the result JSON carries back to the host (docs/design/done/WASM_TIER2_PLAN.md D4).

Variants

Stdout

Stream to process stdout immediately (native CLI / WASI).

Capture(String)

Capture into a buffer (reactor) — returned as the result’s output.