Constant SEARCH_DOC 

pub const SEARCH_DOC: &str = "Search posts by keyword (default) or semantic similarity. \
     Comments are out of scope for both modes — only posts are indexed.\n\n\
     `mode=\"keyword\"` (default): Postgres full-text search (`tsvector`/`ts_rank`) over \
     post titles and bodies. Always available.\n\n\
     `mode=\"semantic\"`: nearest-neighbor search over post embeddings by cosine \
     similarity, floored so unrelated posts aren't padded in just to fill a result \
     count. Finds conceptually related posts that share no keywords. Needs the \
     server's embedding backend: a freshly created post isn't embedded yet and won't \
     surface in semantic results for up to ~2 minutes (the embedding sweep interval); \
     an edited post keeps searching under its original text (posts are only ever \
     embedded once). If the embedding backend is unavailable, times out, or the \
     server has none configured, the search silently downgrades to keyword instead \
     of erroring \u{2014} check `degraded` and `mode_used` in the response rather than \
     assuming the requested mode ran.";

What search does, in both modes