# Bounded echo output (K1281–K1285)

`Echo<N>` encodes UTF-8 words with one space between words and an optional
trailing newline. NUL bytes and capacity overflow reject the complete request
before any output. No heap allocation is used.

`emit` uses the bounded user-runtime writer. Every acknowledged byte advances
the cursor, including when a later write fails. A retry starts at that cursor,
so an injected short write or error does not duplicate acknowledged output.
The caller owns the writer and the encoded buffer throughout.

Host tests and an AArch64 `no_std` check establish the local state behavior.
EL0 serial output, guest acceptance and product release require separate
evidence.