fn hex(y: &Yaml, want: usize, what: &'static str) -> Result<Bytes, String>Expand description
A trace or span id: lowercase or uppercase hex, exactly want bytes.
Absent and all-zero are both “no id” in OTLP and both reach the encoder as an
empty Bytes. A wrong length is an error instead, because the alternative
is storing a truncated id that will never join to anything and never explain
why.