Function rdf_lov_undefined_prefix_completion 

pub fn rdf_lov_undefined_prefix_completion(
    query: Query<'_, '_, (&TokenComponent, &Source, &RopeC, &Prefixes, &mut CompletionRequest, &DynLang)>,
    lovs: Query<'_, '_, &LocalPrefix>,
    prefix_cc: Query<'_, '_, &PrefixEntry>,
    config: Res<'_, ServerConfig>,
)

Generic prefix completion for the text RDF languages (Turtle / TriG / SPARQL).

Suggests prefixes from the local LOV data, the prefix.cc list, and the prefixes already declared in the document. When the chosen prefix is not yet declared, the language’s prefix_edits supplies an additional edit that inserts the declaration; when it is already declared no such edit is added.

This is registered once (in the shared completion schedule) and dispatches per-document through DynLang, so it does not need a language marker filter. Languages whose prefix model is incompatible (e.g. JSON-LD @context) opt out via handles_prefix_completion.