* fix: bypass FTS5 for CJK queries in session_search
FTS5 default tokenizer splits CJK characters into individual tokens,
so multi-character queries like "大别山项目" become AND of single chars.
This produces few/no results compared to LIKE substring search.
For CJK queries, skip FTS5 entirely and use LIKE for accurate
phrase matching.
Fixes NousResearch/hermes-agent#15500
* fix: cache _contains_cjk, escape LIKE wildcards, add regression tests
On top of the CJK FTS5 bypass from #15509:
- Cache _contains_cjk() result in a local var to avoid redundant O(n)
scans on every CJK query
- Escape %, _ in LIKE queries so literal wildcards in user input are
not treated as SQL wildcards (consistent with other LIKE queries in
hermes_state.py that use ESCAPE '\')
- Fix misleading comment ('or CJK fallback' → accurate description)
- Add 3 regression tests:
- test_cjk_partial_fts5_results_supplemented_by_like (#15500 / #14829)
- test_cjk_like_dedup_no_duplicates
- test_cjk_like_escapes_wildcards (new wildcard escaping)
* feat: trigram FTS5 index for CJK search, replace LIKE fallback
Replace the LIKE '%query%' full-table-scan fallback for CJK queries with
a proper trigram FTS5 index (messages_fts_trigram). The trigram tokenizer
creates overlapping 3-byte sequences so substring matching works natively
for any script — CJK, Thai, etc.
For queries with 3+ CJK characters: uses the trigram FTS5 table with
proper ranking, snippets, and indexed lookups. For shorter queries
(1-2 CJK chars): falls back to LIKE since the trigram tokenizer needs
≥9 UTF-8 bytes (3 CJK chars) minimum.
Schema v10 migration creates the trigram table and backfills existing
messages. Triggers keep the index in sync on INSERT/UPDATE/DELETE.
Builds on top of #16276 (bypass FTS5 for CJK, escape LIKE wildcards).
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Co-authored-by: vominh1919 <vominh1919@gmail.com>
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