fix(session_search): supplement FTS5 with LIKE for CJK partial results (#14829)

FTS5 unicode61 tokenizer drops certain CJK characters, causing queries
like '昨晚' to return only 12.5% of actual matches. The existing LIKE
fallback only triggers when FTS5 returns zero results, missing the
common case where FTS5 returns *some* but not all matches.

Change the LIKE path from a fallback (only on empty results) to a
supplement (always runs for CJK queries). Results are merged with
deduplication by message id, so FTS5 results are preserved and LIKE
fills in what FTS5 missed.

- Always run LIKE for CJK queries, not just on zero FTS5 results
- Deduplicate merged results by message id
- Add regression test for partial-result supplementation
- Add deduplication correctness test

tests/test_hermes_state.py

@@ -716,6 +716,33 @@ class TestCJKSearchFallback:
         results = db.search_messages("Agent通信")
         assert len(results) == 1
 
+    def test_cjk_partial_fts5_results_supplemented_by_like(self, db):
+        """When FTS5 returns *some* CJK results, LIKE must supplement them.
+
+        Regression test for #14829: FTS5 unicode61 tokenizer drops certain
+        CJK characters, so multi-character queries may return partial results.
+        The LIKE path must always run for CJK queries and merge results.
+        """
+        db.create_session(session_id="s1", source="cli")
+        db.create_session(session_id="s2", source="telegram")
+        # Insert messages containing the same CJK substring.
+        # FTS5 may index one but not the other depending on tokenizer quirks.
+        db.append_message("s1", role="user", content="昨晚讨论了记忆系统")
+        db.append_message("s2", role="user", content="昨晚的会议纪要已发送")
+        results = db.search_messages("昨晚")
+        # Both messages contain "昨晚" — LIKE must find both even if FTS5
+        # only returns one (or zero). Dedup ensures no duplicates.
+        assert len(results) == 2
+        session_ids = {r["session_id"] for r in results}
+        assert session_ids == {"s1", "s2"}
+
+    def test_cjk_like_dedup_no_duplicates(self, db):
+        """When FTS5 and LIKE both find the same message, no duplicates."""
+        db.create_session(session_id="s1", source="cli")
+        db.append_message("s1", role="user", content="测试去重逻辑")
+        results = db.search_messages("测试")
+        assert len(results) == 1
+
 
 # =========================================================================
 # Session search and listing