evalExpr was missing irekSubquery case — scalar subqueries in SELECT/WHERE
fell through to else:return "" producing empty strings. Add:
- irekSubquery handler in evalExpr that executes the subquery plan
- outerRow + subqueryPlan fields on ExecutionContext for correlation
- qualified column injection in execScan for correlated filter refs
- collectCorrelatedTablesFromPlan to discover outer table references
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>