If you're building any kind of personal-memory layer on top of SQLite — Claude Code conversation history, notes app, indexed knowledge base — there's a sharp edge in FTS5 that takes most people by surprise the first time they hit it.
The default tokenizer (unicode61) silently drops most Japanese substring queries. The fix is one line of SQL. But the failure mode is invisible enough that you can ship a personal search tool, use it for weeks, and never realize half your content is unreachable.
This post walks through:
The failure, reproducible in 20 lines of Python
The one-line fix (tokenize='trigram') and what it actually does under the hood
