The DISTINCT keyword on a WITH clause was parsed (r->distinct) but never
applied, so WITH DISTINCT silently returned duplicate rows. Add a dedup pass
in execute_with_clause that drops projected rows whose full value tuple
duplicates an earlier one (first occurrence kept), gated on wc->distinct.
No-op for the aggregation path (which already collapses per group).
Unit test (4 same-label functions collapse to 1 row; control without DISTINCT
keeps 4) plus a query_graph WITH DISTINCT check added to the smoke suite.
Martin Vogel
3014867cb3