fix(falkordb): strip backticks and guard empty token list in fulltext query builder

[octo-patch]

Fixes #1440

Problem

_build_falkor_fulltext_query (and FalkorDriver.build_fulltext_query) had two bugs that caused RediSearch Syntax error failures during dedup-search:

1. Backtick tokens leak through to RediSearch. The separator translation map omitted the backtick character `, so entity names from code-fenced text (e.g. `add_episode`) survived sanitization and broke RediSearch parsing.

2. Empty parenthesis on stopword-only or punctuation-only queries. When every token was filtered out as a stopword (or the input was all separators/backticks), filtered_words became empty but the builder still constructed (@group_id:"…") (), which RediSearch rejects with a syntax error.

Both failure modes existed in two upstream copies of the function:

• graphiti_core/driver/falkordb/operations/search_ops.py — _build_falkor_fulltext_query
• graphiti_core/driver/falkordb_driver.py — FalkorDriver.sanitize / build_fulltext_query

Solution

Two surgical changes applied to both copies:

1. Add ` to the separator translation map so backticks are replaced with whitespace before tokenization.
2. Return '' early when filtered_words is empty after stopword filtering, so callers skip the RediSearch query rather than issuing a malformed one.

Testing

Added unit tests in tests/driver/test_falkordb_driver.py covering:

• Backtick tokens are stripped from the query string
• Stopword-only queries return ''
• Punctuation-only queries return ''
• Backtick-only queries return ''
• Normal queries still produce valid non-empty results
• Backtick mixed with normal tokens strips backticks but keeps the tokens

All 6 new tests pass. No existing tests were broken.

[robowen1]

Reporter here — thanks for picking this up so quickly. The diff matches what I monkey-patched locally to validate the issue, and I can confirm the same fix took my Sonnet 4.6 + FalkorDB corpus rerender from ~30% failure (16/55 episodes) to 0%

Quick note on correctness: returning '' is the right contract — it matches the existing max_query_length overflow branch, and the FalkorSearchOperations.{node,edge,episode,community}_fulltext_search callers already short-circuit on fuzzy_query == '' with return []. So no caller changes are needed and the malformed (@group_id:…) () can't be constructed.

LGTM — happy to see this land.