FTS5 query crashes on unescaped metacharacters (apostrophe, quotes)

[coreyt]

Problem

When a user query contains FTS5 metacharacters (e.g. apostrophe ', double quotes "), text_search() passes the raw string to FTS5, producing:

_fathomdb.SqliteError: fts5: syntax error near "'"

This was hit in production when Memex's retrieval layer searched for User's name — the apostrophe broke the FTS5 query parser.

Reproduction

engine = Engine.open("test.db")
# ... register a collection with text_search support ...
q = engine.nodes("some_kind").text_search("User's name", limit=10)
q.execute()  # -> SqliteError: fts5: syntax error near "'"

Expected behavior

text_search() should escape FTS5 metacharacters in the query string before passing it to the FTS5 MATCH expression. At minimum, double any embedded double-quotes and wrap each token in double quotes, e.g. "User's" "name".

Context

• Discovered via Memex service logs (fathom_store.py:2544 → _query.py:254)
• The calling code has no way to pre-escape since the query goes through the AST builder
• Affects any text_search() call where the query originates from user input