Function encode_line 

pub fn encode_line(value: &impl Serialize) -> String

Serializes value to a single JSON-RPC line with no trailing newline — the caller appends \n when writing it to a stream (matching decode_line, which also takes one line with the newline already stripped).

serde_json always escapes control characters, including a literal \n, inside string values — a well-formed Serialize impl can therefore never make this produce an embedded newline in the first place. The debug_assert! below is a belt-and-suspenders guarantee against a future custom Serialize impl breaking that invariant, not a runtime check this protocol expects to ever fire.