fix: WHERE filter pushdown silently corrupts OR/CASE queries

[jxom]

Audit Finding

WHERE Filter Pushdown Silently Corrupts Queries with OR/CASE Expressions by Forcing AND Restrictions on CTE (Severity: High)

Problem

extract_raw_column_predicates used visit_expressions to walk the entire AST, which extracted predicates from inside OR branches and CASE arms. These were then pushed down as AND restrictions on the CTE, silently changing query semantics.

For example:

SELECT * FROM Transfer WHERE block_num > 100 OR address = '0xABC'

Would incorrectly push block_num > 100 as an AND filter on the CTE, filtering out rows that matched address = '0xABC' but had block_num <= 100.

Fix

Replace visit_expressions with explicit WHERE clause extraction that only processes top-level AND conjuncts via flatten_and_conjuncts(). Complex expressions (OR, CASE, nested subexpressions) remain as single opaque conjuncts and are never decomposed for pushdown.

Tests Added

• test_extract_raw_predicates_skips_or_expressions — pure OR not pushed down
• test_extract_raw_predicates_skips_or_mixed_with_and — only safe AND conjuncts pushed down
• test_extract_raw_predicates_skips_case_expressions — CASE not pushed down