Byte-exact counterpart of the pinned ServerFiltered.MarshalYAML output as produced by go-yaml v4 yaml.Marshal (v3-compatible defaults: four-space indent, unlimited line width).

Contract: an accepted value renders exactly the native bytes; anything outside the supported subset is rejected. Supported strings are single-line printable text without tabs; map keys are ASCII with digit runs shorter than 19 digits (native natural ordering is mirrored exactly). Strings whose plain form resolves to another type are double-quoted, YAML 1.1 booleans, base-60 floats and << are single-quoted, and strings the emitter cannot write plain (indicators, leading/trailing spaces, document markers) are single-quoted.