We still want to transform the USING clause into ON, in order to canonicalize those queries. Isn't the only problem here that we're including columns qualified with "r" in the expanded star?

From the linked issue, this is what we produce:

SELECT
  COALESCE("l"."id", "r"."id") AS "id",
  "l"."val_l" AS "val_l",
  "r"."val_r" AS "val_r"
FROM "l" AS "l"
SEMI JOIN "r" AS "r"
  ON "l"."id" = "r"."id"

But as Bill pointed out, if you produce this instead, it works (verified it locally):

SELECT
  "l"."id" AS "id",
  "l"."val_l" AS "val_l"
FROM "l" AS "l"
SEMI JOIN "r" AS "r"
  ON "l"."id" = "r"."id"

That means you need to treat SEMI / ANTI joins specially in the star expansion logic to avoid introducing "r".<column> projections. Notice that having "r"."id" in the join condition doesn't cause any issues.

I unblocked the USING expansion by adding a new map on Scope which collects the SEMI/ANTI join tables as "pseudo" selected sources in order to bypass validate_qualify_columns.