Constant SNIPPET_PAYLOAD_KIND_ID 

pub const SNIPPET_PAYLOAD_KIND_ID: u32 = 2;

Extension-payload kind tag for snippet candidates. Carried in RawCandidate::data so the host’s snippet_meta_for reader can route the payload back through SnippetRegistry::by_name. Value matches the host’s historic SNIPPET_COMPLETION_KIND_ID = 2 so the existing accept path keeps recognising snippet candidates without a flag day. Stable u32 – changing it breaks every snippet candidate’s accept path.