Port from nearai/ironclaw#7553 (Filter::FtsRanked): FTS5's implicit AND
between terms means a paraphrased multi-word query misses a stored
sentence that lacks even one of the words. When the exact-match search
and the substring fallbacks all return zero rows, retry the same
unicode61 FTS index with the terms OR-joined, ranked by bm25 so rows
covering more terms surface first.
Strictly additive: gated on a zero-result miss, so successful searches
keep exact-match semantics and ordering. Queries with explicit OR/NOT,
single-term queries, and CJK-routed queries are left untouched. Quoted
phrases relax as whole units.
Adapted for hermes-agent: implemented inside SessionSearchMixin's
zero-result fallback chain (after the CJK-bigram/trigram substring
retries) rather than as a separate filter variant, reusing the already-
built SQL/params so all source/role/sort filters apply to the retry.
Teknium
2a2c3aa588