Fix #1219: quote-aware pattern-existence pre-scan + whitebox tests

[lmeyerov]

Summary

Fixes a concrete #1219 front-end policy-boundary bug found during whitebox amplification.

The parser's pre-parse unsupported-form check for pattern-existence syntax (exists { ... }, not((pattern))) previously scanned raw query text, so it falsely rejected valid row-only queries when those lexemes appeared inside string literals.

This PR makes the pre-scan quote/backtick-aware and adds regression coverage.

Changes

• graphistry/compute/gfql/cypher/parser.py
  • Added masking helper for quoted/backticked spans before unsupported-pattern regex checks.
  • _check_unsupported_syntax_patterns() now scans masked text.
• graphistry/tests/compute/gfql/cypher/test_parser.py
  • Added parser tests proving quoted lexemes are accepted.
  • Added guard tests proving true pattern-existence expressions still reject.
• graphistry/tests/compute/gfql/cypher/test_where_row_boolean_policy_boundary.py
  • Added runtime boundary test proving quoted lexemes behave as row literals.
• CHANGELOG.md
  • Added Development/Internal note for the fix.

Validation

• python -m pytest -q graphistry/tests/compute/gfql/cypher/test_parser.py -k "pattern_existence_lexemes_inside_string_literals or still_rejects_true_pattern_existence"
  • 7 passed, 115 deselected
• python -m pytest -q graphistry/tests/compute/gfql/cypher/test_where_row_boolean_policy_boundary.py
  • 10 passed
• python -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k "pattern_existence"
  • 4 passed, 881 deselected
• UV_CACHE_DIR=/tmp/uv-cache uv run ruff check graphistry/compute/gfql/cypher/parser.py graphistry/tests/compute/gfql/cypher/test_parser.py graphistry/tests/compute/gfql/cypher/test_where_row_boolean_policy_boundary.py
  • All checks passed

Refs #1219