Spec deltas
Per-capability spec changes proposed by define-hybrid-retrieval.
PDPP SHALL define an optional experimental hybrid-retrieval extension for implementations that combine lexical and semantic retrieval into one result list. Clients SHALL NOT assume the extension exists unless resource-server metadata advertises it.
GET /v1/search SHALL remain the lexical retrieval endpoint even when a server also advertises hybrid retrieval. Hybrid retrieval SHALL NOT silently alter lexical result ranking, filtering, scoring, or response shape.
GET /v1/search/semantic SHALL remain the semantic retrieval endpoint even when a server also advertises hybrid retrieval. Hybrid retrieval SHALL NOT silently alter semantic result ranking, filtering, scoring, model identity, or response shape.