[Fruiterer333]

Please ensure you have read the contribution guide before creating a pull request.

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: SqliteMemoryService with FTS5 finds nothing for a Chinese or Japanese keyword inside a sentence #7959

Problem:
With FTS5 (the default, fts="auto"), SqliteMemoryService cannot find a Chinese or Japanese word inside a stored sentence. The unicode61 tokenizer indexes 我想买这辆车，价格是二十万。 as two tokens, 我想买这辆车 and 价格是二十万, so searching 价格 or 二十万 returns nothing. The same search works with fts="off" and with InMemoryMemoryService.

Solution:
When a query token contains a Chinese or Japanese character (CJK ideographs, hiragana, katakana), search_memory uses the existing LIKE path instead of FTS5. That path already matches tokens as substrings, so it is what fts="off" does today.

• No schema change and no re-indexing: existing databases work as they are.
• Queries without Chinese or Japanese characters still use FTS5 and bm25 ranking, unchanged.
• Trade-off: these queries rank by the number of matched tokens, then by time (the LIKE path's ranking), instead of bm25, and they scan the user's rows instead of using the index.

I did not change other scripts written without spaces (e.g. Thai), since I have not tested them.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Added test_search_matches_cjk_word_inside_sentence in tests/unittests/memory/test_sqlite_memory_service.py. It runs in both fts="on" and fts="off" modes with four cases: 价格 and 二十万 in a Chinese sentence, and 使う and Python 使う in 私はPythonを使う. Before the fix, the three Chinese/Japanese-only cases fail in fts="on" mode.

$ pytest tests/unittests/memory/test_sqlite_memory_service.py
72 passed
$ pytest tests/unittests/memory/
208 passed

pre-commit run --files on the two changed files passes (ruff, isort, pyink, codespell, ADK compliance checks).

Manual End-to-End (E2E) Tests:

Ran the reproduction script from the issue.

Before:

SqliteMemoryService(fts='auto')    query='价格'       -> 0 memories
SqliteMemoryService(fts='auto')    query='二十万'      -> 0 memories

After:

InMemoryMemoryService              query='price'    -> 1 memories
InMemoryMemoryService              query='价格'       -> 1 memories
InMemoryMemoryService              query='二十万'      -> 1 memories
SqliteMemoryService(fts='auto')    query='price'    -> 1 memories
SqliteMemoryService(fts='auto')    query='价格'       -> 1 memories
SqliteMemoryService(fts='auto')    query='二十万'      -> 1 memories
SqliteMemoryService(fts='off')     query='price'    -> 1 memories
SqliteMemoryService(fts='off')     query='价格'       -> 1 memories
SqliteMemoryService(fts='off')     query='二十万'      -> 1 memories

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

I used Claude Code to help find the issue and draft the fix. I reproduced the bug and verified the fix locally myself.