go.yaml.in/yaml/v4 rc.6 Marshal drops leading spaces after a leading newline

With go.yaml.in/yaml/v4 v4.0.0-rc.6, yaml.Marshal("\n x") emits |-\n\n x with no indentation indicator, so every parser (go-yaml itself included) reads it back as "\nx". The same happens for any string whose first non-empty line starts with a space after leading empty lines. It's fixed on main: the 2026-10-30 pseudo-version (go get go.yaml.in/yaml/v4@main) emits |4- and round-trips. gopkg.in/yaml.v3 3.0.1 has a worse variant: Marshal("\na") gives |4-\n a and loses the leading newline; go.yaml.in/yaml/v3 3.0.5 is fixed. If you marshal user strings, pin past rc.6 or test Unmarshal(Marshal(s)) == s.